| 1. | Christian Aganze, Stanford University Poster: Mapping the Cocytos Stream with DESI: Insights into its Galactic Origin and Connection with Gaia-Enceladus July 10, 2024 PDF, 10.91 MB In the current galaxy formation paradigm, the Milky Way’s halo was built up by accreting dwarf galaxy progenitors. The discovery, census, and characterization of stellar streams in the Milky Way help complete this picture by constraining the number of visible Milky Way dwarf galaxies and the number of invisible dark subhalos by their gravitational interactions with streams and the formation of Globular clusters. The DESI Milky Way survey covers a 14,000 sq. deg footprint with a depth of r=19 mag. With these capabilities, it provides the largest sample of distant (>10 kpc) metal-poor stars compared to previous optical fiber-fed spectroscopic surveys. In this work, we present a characterization of the Cocytos stream, which was re-discovered using a clustering analysis with a catalog of DESI giants in the DESI Year 1 data. We supplemented these data with additional Gaia astrometry and Magellan/MagE spectroscopy. Our analysis reveals a metal-rich ([Fe/H]=-1.3), thick stream (width=1.7 deg), at a distance of ~26 kpc, with low internal velocity dispersion (~10km/s). Combining these measurements, the orbital parameters of the stream, and previous kinematic associations with the Virgo Overdensities, we speculate that the Cocytos stream is a result of a disrupted globular cluster that came in with the Gaia-Enceladus merger. Our precise radial velocity data help isolate the stream from other nearby structures, which will aid further characterization with future surveys. Additionally, our result showcases the need for spectroscopic follow-up of photometrically-discovered streams in the LSST era. |
| 2. | Jose Benavides, University of California - Riverside Poster: The inefficient star formation in Ultra-diffuse galaxies and their stellar populations July 10, 2024 Low surface brightness galaxies are one of the most interesting objects that can be studied using data taken from telescopes such as the LSST. In the dwarf galaxy regime, ultra-diffuse galaxies (UDGs) are one of the objects that has attracted the attention of the scientific community, without an absolute consensus on their formation mechanism. Using data from the TNG50 simulation we study the stellar properties of a sample of simulated UDGs star-forming and quenched. We find that, on average, star-forming UDGs were formed on dark matter halos 40 –70 % higher than non-UDG at a given stellar mass. Also, UDGs (star-forming or quench) are approximately 70% less enriched in [Fe/H] compared to the non-UDG population with similar masses. The sample simulated galaxies in TNG50 present metallicity profiles with a very steep negative gradient, in contrast to flatter profiles obtained from other mechanisms of formation as, for example, associated with feedback. In terms of star formation histories, UDGs and non-UDGs exhibit good agreement in both cases star-forming or quenched. However, in the case of UDGs generally tend to have shorter quenching time scales than their non-UDG counterparts. The predictions made by this type of cosmological simulations are of vital importance for these new observational surveys. |
| 3. | Joy Bhattacharyya, Ohio State University Poster: Field Dwarf Galaxies: how isolation shapes their properties in TNG50 July 9, 2024 PDF, 1.58 MB Dwarf galaxies are essential to test dark matter physics at the mass scales of their halos. The primary focus of earlier investigations have been on dwarfs that form the substructures of massive galaxies. However to better understand the physics of the dwarf scale halos, we need to consider field dwarfs that are isolated from any massive galaxy. For this purpose we use the Illustris TNG50 suite of cosmological simulations to study dwarfs in halos with virial masses $10^{10} M_{odot} <mathcal{M}_{200} < 10^{11.5} M_{odot}$. The field dwarfs are identified as those which are the centrals of their dark matter halos. We then quantify their local environmental density by using both the tidal index $Theta_1$ and the distance to the nearest massive galaxy $d_{host}$. Based on the density metrics we study how the gas contents, star formation rates (SFR) and mass-to-light ratios of the dwarf galaxies depend on how isolated they are. We also find two distinct types of systems- dwarf centrals that are the only galaxies in their halos and dwarf associations with a few member galaxies in their halo. We aim to use these samples of field dwarfs to develop calibrations between the properties of the parent dark matter halos and the observable baryonic content. Such calibrations will be useful given the large samples of field dwarfs that we expect to detect using galaxy surveys like Merian, DESI and LSST in the future. This study informs where to find such isolated field dwarfs in the local universe and also how their properties may depend on their environment and dark matter content. |
| 4. | Daisy Bissonette, University of Chicago Poster: The Metallicity Distribution of the Primitive Ultra-Faint Dwarf Galaxy Segue 1 July 10, 2024 PDF, 0.92 MB Segue 1 is one of the smallest, lowest luminosity, most dark matter-dominated, and most metal-poor ultra-faint dwarf galaxies that has been observed. Previous work has shown that Segue 1 has a unique, multi-modal metallicity distribution with a large range of metallicities spanning over two orders of magnitude. Using low-resolution spectroscopy from Keck/LRIS observations of the main sequence turnoff population in Segue 1, this work measures the metallicity distribution for a statistically significant sample of ~40 stars, five times more than similarly low mass (~1000 solar masses) galaxies. Metallicities for metal-poor main sequence turnoff stars can be measured from low-resolution spectra using the Ca K line at 3933 Angstroms. These measurements provide a new detailed view into the extreme formation history of Segue 1, a relic from the era of first star and galaxy formation. |
| 5. | |
| 6. | Mike Boylan-Kolchin, University of Texas Austin Invited Talk: Galaxy Formation Physics Revealed by Faint Stellar Systems Near and Far July 9, 2024 (9:00 AM) PDF, 5.18 MB The faintest nearby galaxies are also the most metal-poor and have the shallowest gravitational potential wells; many are likely relics of the high-redshift Universe that would be far too dim to observe directly during their formation. Globular clusters are similarly faint and old but are relics of a different mode of star formation, one that JWST is revealing in situ in the high-redshift Universe. I will discuss how faint galaxies and globular clusters both near and far offer unique opportunities to learn about galaxy formation physics. I will also describe ongoing efforts to connect these faint stellar systems across cosmic time. |
| 7. | Joseph Breneman, Rutgers University Poster: Exploring the Chemical Evolution Pathways of the Extremely Metal-poor Dwarf Galaxy Leonessa July 9, 2024 PDF, 1.32 MB Extremely metal-poor galaxies (XMP) are systems with gas-phase oxygen abundances below 5% Solar metallicity (12+log(O/H) ≤ 7.35). These galaxies populate the faint-end of the luminosity function, the metal-poor end of the mass-metallicity relation (MZR), and similarly the luminosity-metallicity relation (LZR). Recent studies have found XMP galaxies in the nearby Universe to be outliers on the LZR, where they show a lower metallicity than other galaxies of similar luminosity. Initially, it was thought that nearby XMP galaxies were chemically unevolved systems (<1Gyr) and forming their first stars. However, follow-up observations have resolved older stellar populations in these galaxies, indicating earlier enrichment epochs. I will present results on a newly discovered XMP galaxy, Leonessa, and characterize the system’s properties using recent observations obtained from the HST, GBT, and HET Telescope. Leonessa is a gas-rich, star-forming galaxy located in a nearby void (D=15.67±0.65 Mpc) with a gas-phase oxygen abundance of only 7.32±0.04. Leonessa agrees with the MZR trend, but joins other XMP galaxies as an outlier on the LZR trend. We find evidence that metal-biased outflows have likely been a strong contributor to the low gas-phase abundance observed in Leonessa. To provide additional context for the properties of XMP galaxies in the nearby universe, I will also present a comparison sample of 155 dwarf galaxies, including 58 XMP systems, with gas-phase metallicity measurements based on the ‘direct’ method. Despite observed XMP galaxies being found to have a high surface brightness, their compact morphology, and low stellar masses make them faint objects in the sky. The LSST survey will expand and improve access to a large portion of the southern celestial sky through its encompassing spatial range and deeper magnitude recovery than previous surveys, leading to the discovery of many more XMP systems to explore. |
| 8. | Julio Carballo-Bello, Universidad de Tarapacá Poster: Exploring the hierarchical formation of the Milky Way with hypervelocity stars July 10, 2024 The exploration of the outer halo of the Milky Way, through wide-sky photometric and spectroscopic surveys, has unequivocally confirmed that the our Galaxy have formed as a result of the continuous merger of protogalactic fragment, aligning with predictions from cosmological Lambda-Cold Dark Matter simulations. Here, we will talk about the hypervelocity stars, considered potential remnants of past accretion events, with velocities exceeding the local escape speed. Alternatively, hypervelocity stars may arise from binary system disruptions during close encounters with the supermassive black hole at the center of the Milky Way. Thanks to the invaluable data provided by Gaia, we have successfully identified stars exhibiting a high likelihood of belonging to this intriguing stellar family. Follow-up VLT spectroscopy has allowed us to estimate their total velocities, which, in certain cases, reach astonishing values of up to 1200 km/s. By reconstructing their past orbits, we have uncovered evidence suggesting that some of these stars might have originated within a now-disrupted dwarf galaxy or experienced another violent event far from the Galactic center. |
| 9. | Jeff Carlin, AURA/Rubin Observatory Invited Talk: Revealing satellites and streams in the Local Volume with LSST July 8, 2024 (1:30 PM) PDF, 8.85 MB |
| 10. | Scott Carlsten, Princeton University Poster: Dwarf Satellites Beyond the Milky Way with the ELVES Survey July 8, 2024 Dwarf satellite galaxies are premier windows into many astrophysical processes, including dark matter, stellar feedback, and the effects of being a satellite of a more massive host. For decades, the satellites in the Local Group (LG) have been the de-facto benchmark for models of small-scale structure. However, to fully understand dwarf evolution, it is crucial to characterize a statistical sample of satellite systems around other MW-like galaxies. To address this, we developed the Exploration of Local VolumE Satellites (ELVES) Survey to characterize the dwarf satellites of 30 Milky Way-like (M* > 10^10 Msun) hosts in the Local Volume down to the faintest `classical satellites', M_V < -9 mag. While we find significant host-to-host scatter in satellite properties, the Milky Way's system appears quite typical along several different axes, including satellite abundance, luminosity function, and quenched fraction. With it's greatly increased statistics, the ELVES Survey has yielded insights into the stellar-to-halo-mass relation for dwarf satellites and the physics of satellite quenching. |
| 11. | William Cerny, Yale University Talk: Understanding the Milky Way's Least Luminous Compact Satellites July 10, 2024 (9:00 AM) Recent large-scale photometric sky surveys have uncovered a burgeoning population of 50+ ultra-faint dwarf galaxies (UFDs) in the Milky Way halo. Follow-up spectroscopy of this shadowy class of systems has revealed that the UFDs are the least chemically-enriched and most dark-matter-dominated galaxies known in the universe. However, the UFDs are not the only class of systems that these surveys have discovered: deep surveys have also revealed a population of exceedingly faint, compact stellar systems at radii < 15 pc, long presumed to be star clusters based on their sizes alone. In this talk, I will present results from the first spectroscopic census of these compact systems -- the ultra-faint star clusters, or UFSCs -- based on new and archival spectroscopic observations of more than 15 systems. Our measurements reveal unexpected similarities between many of the faintest star clusters and the faintest dwarf galaxies, hinting that either (1) some of these compact systems may indeed be galaxies at the very edge of galaxy formation, in concordance with recent semi-analytical models of galaxy formation, or (2) that some UFSCs may have originated within low-mass galaxies that accreted onto the Milky Way. I will conclude by highlighting ongoing and future avenues to understand the nature and origins of the UFSCs. |
| 12. | Yingtian "Bill" Chen, University of Michigan Poster: Unveiling galaxy assembly with star clusters July 10, 2024 PDF, 3.8 MB Massive star clusters, which are bright and compact objects, encode rich information about their interactions with host galaxies. The remnants of dynamically disrupted clusters become stellar streams, while some clusters survive for billions of years, evolving into globular clusters today. However, the connection between a galaxy's assembly history and the features of these stellar associations remains unclear, mainly due to limited observations beyond the Milky Way. To address this challenge, we have developed an comprehensive numerical model for cluster formation, incorporating empirical galaxy scaling relations, particle tagging techniques, and sub-grid models for tidal disruption. Based on this model, we employ an improved particle spray method to simulate the morphology and kinematics of stellar streams from dissolved clusters in realistic galactic potential. The resulting mock catalogs of surviving stellar clusters and streams offer a unique probe into the assembly and structure of galaxies. |
| 13. | Kristin Chiboucas, Gemini Observatory/NSF NOIRLab Poster: Star clusters or stripped galaxies, the UCD population in the Coma Cluster July 9, 2024 Ultra Compact Dwarfs (UCDs) are super massive star clusters found largely in dense regions but have also been found around individual galaxies and in smaller groups. Their origin is still under debate but consensus is that they formed either during major galaxy mergers as mergers of super star clusters, are simply the high mass end of the globular cluster luminosity function, or that they formed from the threshing of galaxies and are remnant nuclear star clusters. Evidence now suggests that they may have formed through multiple pathways. We are attempting to disentangle these competing formation scenarios with a large survey of UCDs in the Coma cluster. With ACS two-passband imaging from the HST/ACS Coma Cluster Treasury Survey, we are using colors and sizes to identify the UCD cluster members. With upcoming JWST cycle 3 NIRCam and NIRISS imaging data, we will be able to extract additional high spatial resolution and IR color information to help us better distinguish between stellar/background galaxy contaminants and UCDs and we will be able to expand our search for UCDs to larger distances from the cluster center. Understanding their abundance and distribution throughout the cluster in conjunction with the GC and dwarf galaxy populations, and in comparison with models, will be key to understanding the fraction of the UCDs in this rich environment that constitute remnant nuclear star clusters from stripped dwarf galaxies as opposed to bright GCs or super star clusters. |
| 14. | Benjamin Cohen, University of Chicago Poster: Sifting for a Stream: An Analysis of the Morphology of the 300S Stellar Stream July 10, 2024 PDF, 3.84 MB Stellar streams are sensitive laboratories for understanding the Galactic potential's small-scale structure. Here, we analyze the morphology of the 300S stellar stream. Because 300S is on a highly eccentric, retrograde orbit, it has potential to be an especially powerful probe of both baryonic and dark substructures within the Milky Way. We use photometric information from Dark Energy Camera Legacy Survey DR9 and kinematic information from Gaia DR3 to characterize the stream's morphology over ~20 degrees in the presence of extensive background structure from the Sagittarius stream. We redetermine the stream coordinate system and distance gradient using photometry, RR Lyrae stars, and spectroscopic members from the Southern Stellar Stream Spectroscopic Survey (S5). We then apply two distinct approaches to determine 300S’s morphology. First, we analyze stars from Gaia using proper motions to remove the Sagittarius stream. Second, we generate a simultaneous model of 300S and Sagittarius based purely on photometric information, by performing a transformation between stellar density maps filtered under different distance gradients. We find that 300S's stellar density has a well-defined peak and neither sharp density structures nor sharp variations in stream width. This is the first model of 300S's morphology across its entire footprint, opening the doors for deeper analysis to probe the structures of the Milky Way. |
| 15. | Brian Cook, University of North Carolina at Chapel Hill Poster: Faint Substructure Candidate Identification with Galactic Standard Candles in Wide-Field Survey Data July 10, 2024 PDF, 0.31 MB We present a new routine for finding distant open clusters and ultrafaint dwarf galaxies in the Milky Way via near-field standard candles. Our routine was applied to the Gaia DR3 database of RR Lyrae variables (RRLs); after a round of pre-processing to ensure that an accurate RRL phase-space distribution could be rendered, we employed significance mapping and hierarchical, density-based spatial clustering to detect previously undiscovered compact satellites. We implement several false positive mitigation strategies and cross-check each candidate with associated stars at the tip of the red-giant branch (another standard candle found in evolved stellar populations). The aggregate of these routines yielded two new open cluster candidates; both would constitute the furthest detected open clusters. The Gaia brightness limit, however, precludes us from detecting the candidates’ main sequence stars. LSST will observe both candidate regions >100 times in the 10 years (ideal for follow-up studies) and provide deeper standard candle databases to which this routine can be applied. |
| 16. | Mia de los Reyes, Amherst College Poster: Stellar Mass Calibrations in Low-Mass Galaxies July 9, 2024 PDF, 1.02 MB The stellar mass of a galaxy traces the galaxy’s cumulative history of growth. While several works have tested the robustness of stellar mass measurement techniques, these tests have typically not extended to low-mass (<1e8 Msun) dwarf galaxies. This low-mass regime poses unique problems for measuring stellar mass from integrated light: dwarf galaxies have complex star formation histories that are difficult to model, and many empirical calibrations rely on survey data that are incomplete at low masses. Here we test a number of stellar mass measurement techniques on simulated dwarf galaxies. We identify some best practices for measuring dwarf galaxy masses using optical colors, which is crucial as LSST begins discovering and characterizing new populations of dwarf galaxies. |
| 17. | Amandine Doliva-Dolinsky, University of Tampa; Dartmouth College Poster: Satellites of dwarf galaxies with the MADCASH survey July 8, 2024 Faint dwarf galaxies are powerful cosmological probes as their properties (number, size, luminosity, spatial distribution) can be used to test the cosmological model and, in particular, to constrain the dark matter particle mass. But, to use dwarf galaxies as such, it is absolutely crucial to accurately determine the dwarf galaxy detection limits so they can be accurately modeled into the dwarf galaxy system models. I will present the first such effort to fully characterize the dwarf galaxy system of 11 LMC-SMC type hosts in the Local Volume thanks to the first results of the Magellanic Analog Dwarf Companions And Stellar Halos (MADCASH) survey. This wide field imaging survey allows us to detect the very faint satellites of these systems, which are essential to constrain cosmology and the physics of galaxy formation & evolution. |
| 18. | Mariano Javier de Le Dominguez Romero, IATE-OAc-UNC Poster: A study of gravitational wakes by satellite galaxies in the MW halo with Gaia DR3 July 10, 2024 PDF, 2.96 MB In Fushimi, K. et al. 2024, we recently used the gravitational wake of the Magellanic Clouds to measure its dark matter halo mass. Any massive subhalo could generate this generic feature, so we explored our galaxies' satellite populations in search of wake signals in a selected population of halo stars. We report updated results and prospects for the upcoming Vera C. Rubin Observatory data. |
| 19. | Adriana Dropulic, Princeton University Talk: StreamGen: Connecting Semi-analytic Tidal Debris to Dark Matter Halos July 10, 2024 (4:20 PM) PDF, 6.65 MB Stellar debris structures are excellent probes of dark matter halos. They are used to constrain tidal disruption rates, trace galactic merger histories, and precisely measure the local gravitational potential. Many streams have been discovered in the Milky Way and in simulations, but this information is statistics-limited, so it is challenging to understand if the distribution of Milky Way streams agrees with LambdaCDM predictions. In this work, we study how the orbital distribution of tidal debris in a semi-analytic galaxy simulation changes systematically as we vary host halo properties. We apply a theoretical model of phase-mixing to satellites in 2,000 galaxies generated by a semi-analytic galaxy simulation, SatGen, to separate populations of streams from both intact satellite galaxies and more phase-mixed structures. Our findings include that the distribution of orbital pericenters and apocenters of streams shifts to lower values with a thicker host disk, higher values with a heavier host disk, slightly lower values in higher-mass host galaxies when a smooth model of baryonic feedback is applied, and higher values for more massive hosts. These results highlight the importance of accounting for variations in host properties when using streams for near-field cosmology and comparing data to simulations. These results can also be used to make predictions of and inform conclusions drawn from the wealth of dwarf galaxy data from the upcoming Rubin Observatory and Roman Space Telescope. |
| 20. | Raphael Errani, Carnegie Mellon University Talk: How Micro Galaxies could help constrain the properties of dark matter July 10, 2024 (9:50 AM) PDF, 2.22 MB Guided by the recent discovery of the faint Milky Way satellite UMa 3/Unions I, in this talk I will present the results of our controlled high-resolution simulations to discuss how micro galaxies could be distinguished observationally from self-gravitating star clusters, and how such systems would help us to constrain both the properties of dark matter and the physical processes underlying the formation of the faintest of galaxies. Micro galaxies are a plausible prediction of Cold Dark Matter (CDM) cosmology: The centrally-divergent density cusps of CDM subhaloes render them remarkably resilient to tides. Heavily stripped tidal remnants of the Milky Way accretion may survive even in the strong tidal field of the inner regions of our Galaxy. Some of these tidal remnants may have been sufficiently massive in the past to allow for star formation within their potential wells, giving rise to a population of micro galaxies: co-moving groups of stars, gravitationally supported by the dark matter subhalo which surrounds them. |
| 21. | Peter Ferguson, University of Wisconsin - Madison Invited Talk: LSST Overview July 10, 2024 (11:30 AM) PDF, 4.52 MB |
| 22. | Peter Ferguson, University of Wisconsin - Madison Poster: Harnessing Synthetic Source Injection to explore the Local Volume in the LSST Era July 8, 2024 Rubin Observatory's decade-long survey will provide an extraordinarily rich photometric dataset to discover and characterize (sub)structures in the Local Volume. In order to address the new challenges this deeper data brings, such as star galaxy separation and blending, and fully leverage this dataset for new discoveries it is vital that we develop a deep understanding of survey systematics. Synthetic Source Injection (SSI) is one such powerful tool that we can use. This method involves injecting sources with known properties into pixel-level data. These injected images are then processed using the same algorithms applied to actual observations and can be used to infer biases in our data products. In particular, we discuss the application of SSI on precursor datasets, such as the Dark Energy Survey (DES), to assess the observational selection function—specifically stellar completeness and contamination— as a function of different survey properties and how this will enable an accurate characterization of density variations in stellar streams. Additionally, we present a framework to inject realistic stellar populations within the Rubin Science Pipelines, highlighting how this framework will enable machine learning approaches to finding distant isolated dwarfs in LSST data. |
| 23. | Catherine Fielder, University of Arizona Poster: Confirmation of Stellar Halos Built by Accretion at the Dwarf Galaxy Scale July 8, 2024 PDF, 4.95 MB I present deep optical observations of the stellar halo of NGC 300, an LMC-mass system, acquired through the Blanco DECam DELVE-DEEP sub-survey. Analysis reveals a significant discovery: a large, low surface brightness stellar stream extending more than 40 kpc from the galaxy's center, northward, in addition to other shell structures and a potential stream wrap. While it is well established that stellar halos and substructures reflective of accretion history exist at the Milky Way-mass scale, it remains unclear whether dwarf galaxies harbor similar structures and whether these halos form through accretion or in situ processes such as star formation-driven radial migration. These findings mark the first evidence supporting accretion as a viable mechanism for forming stellar halos in the LMC-mass range beyond the Local Group, shedding light on the intricate dynamics of dwarf galaxy evolution. This work is a precursor for the discoveries that will be possible in the southern sky with Rubin Observatory. |
| 24. | Sal Fu, UC Berkeley Talk: Detailed Views Into the Baryon Cycle of Dwarf Galaxies from HST Narrowband Imaging July 9, 2024 (4:00 PM) PDF, 19.8 MB We present hundreds of new stellar metallicities in faint, Local Group dwarf galaxies measured through a novel use of HST narrowband Ca H&K imaging. Our imaging includes 463 stars in 13 ultra-faint dwarf galaxies (UFDs) around the Milky Way, which effectively doubles the number of stellar metallicities in all known UFDs. It also includes 374 stellar metallicities in the quenched field dwarf galaxy Tucana, a factor of ~7 increase over literature spectroscopy. We will present highlights from the wide range of science cases enabled by our data, which include: 1) chemical evolution modeling to put novel constraints on the baryon cycle in UFDs, 2) new metallicity benchmarks for cosmological simulations of the faintest galaxies, 3) high-fidelity metallicity gradients that constrain stellar feedback and DM core formation models in dwarf galaxies. We conclude with a discussion on the immense scientific potential of using Ca H&K for stellar metallicities outside the LG. |
| 25. | Marla Geha, Yale Talk: The SAGA Survey: A Census of 101 Satellite Systems around Milky Way-like Galaxies July 9, 2024 (2:00 PM) PDF, 29.31 MB We present the main findings of the third Data Release (DR3) of the Satellites Around Galactic Analogs (SAGA) Survey, a spectroscopic survey characterizing satellite galaxies around Milky Way (MW)-mass galaxies. SAGA DR3 includes 378 satellites identified across 101 MW-mass systems. We will discuss DR3 results on the quenched fraction of satellites, luminosity functions, radial distributions and star-formation properties. We will then consider the opportunities and challenges in extending this work in the LSST era. |
| 26. | Katya Gozman, University of Michigan Poster: Exposing the diversity of ultra-faint satellites in the M81 group July 8, 2024 PDF, 4.26 MB In the last decade, we have been able to probe further down the galaxy luminosity function than ever before and expand into the regime of ultra-faint dwarfs (UFDs), which are some of the best probes we have of small-scale cosmology and galaxy formation. Digital sky surveys have enabled the discovery and study of these incredibly low-mass, highly dark-matter dominated systems around the Local Group, but it is critical that we expand the satellite census further out to understand if Milky Way and M31 satellites are representative of dwarf populations in the local universe. Using data from HST/ACS, we present updated characterization of four satellite systems in the M81 group. Three of these systems – D1005+68, D1006+69 and D1009+68 – were previously discovered using ground-based Subaru HSC data. The other – J0954+6821 – was first found as a dwarf galaxy candidate by Bell et al. 2023 as an overdensity in M81’s halo and is now confirmed with HST/ACS by this work. These are all faint (Mv > -7.6) and consistent with old (~13 Gyr), metal-poor ([M/H] < -1.2 ) populations. Each of these systems possess relatively unusual features – from one of the most concentrated satellite galaxies with a Sérsic index of n~5, to a Hercules-analog with an ellipticity of 0.72, to one of the most compact galaxies for its magnitude. Two of these satellites are also amongst the lowest surface brightness galaxies that we know of, a factor of 100 lower surface brightness than those typical of ultra-diffuse galaxies. This work shows the scientific promise of the upcoming Rubin Observatory and Roman Telescope for illuminating the diversity of UFDs in the Local Volume and beyond. |
| 27. | Jenny Greene, Princeton University Invited Talk: Observational frontiers in dwarf galaxies beyond the Local Group July 9, 2024 (1:30 PM) PDF, 76.03 MB |
| 28. | Thales Gutcke, IfA, Hawaii Invited Talk: LYRA: Simulating dwarf galaxies that form globular clusters and are tested in self-interacting dark matter July 9, 2024 (3:30 PM) I will introduce LYRA, a pioneering cosmological galaxy formation model using moving-mesh hydrodynamics that resolves every single massive star, and resulting supernova from first principles. To accomplish this, the simulation is run at ultra-high resolution (~1pc), includes a multi-phase interstellar medium, and traces the star formation and assembly of mini halos across cosmic time to form present-day dwarf spheroidals. I will demonstrate the efficacy of the model on a set of field dwarf galaxies that match the stellar mass, size, stellar kinematics and metallicity relations of Local Group dwarf spheroidals at z=0. I proceed to present the properties of the population of globular clusters and their self-consistent formation within the simulations. The GC size – mass relation and the GC mass – halo mass relation are well matched. Additionally, I will show preliminary work on a self-interacting dark matter counterpart simulation, presenting how the central DM core affects observables such as central surface brightness and number of GCs in the central region. |
| 29. | Tehreem Hai, Rutgers University Poster: Possibly Quenched Low-mass Galaxy in the Field July 8, 2024 PDF, 1.97 MB We report the discovery of a nearby dwarf galaxy, Canes Venatici C, originally identified in DESI legacy survey data. The galaxy is located at a distance of 9.5+/-0.3 Mpc, measured from the Tip of the Red Giant Branch (TRGB) using follow-up imaging from the Hubble Space Telescope. We use this distance determination to investigate the environment around the galaxy, and find one dwarf galaxy and no massive galaxies within 500 kpc of Canes Venatici C. Based on the color-magnitude diagram, the galaxy shows little evidence of star formation in the last Gyr. These preliminary results suggest that Canes Venatici C may be a quenched, low mass galaxy in the field. |
| 30. | Kai Herron, Dartmouth College Poster: Exploring the Dark Side: Uncovering low-surface brightness galaxies in the Dark Energy Survey July 8, 2024 PDF, 2.12 MB Observations from deep sky surveys have allowed us to uncover more of the universe than ever before. Hidden within these observations are elusive objects known as low-surface brightness galaxies (LSBGs), which are extremely faint, dark matter-dominated objects. Due to their faint nature, LSBGs have been incredibly hard to find, and the need for automated search algorithms has been emphasized in studies of these objects. Understanding the formation mechanisms, the true population of these objects, and what kind of environments they tend to form in are key to helping us fully grasp galaxy evolution and formation. Using observations from Y6 of the Dark Energy Survey, we have been able to develop tools to find these galaxies in a manner which emphasizes completeness of our sample of LSBGs while also removing noisy imaging artifacts. We present the results of our study, characterizing the completeness of our algorithm using simulated galaxies, the approximate size of our sample, and results related to understanding the nature of these objects, all of which will help us prepare for upcoming surveys such as LSST and Roman Space Telescope. |
| 31. | Laura Hunter, Dartmouth College Poster: Satellite Galaxy Candidates Around Low-Mass Hosts July 8, 2024 PDF, 1.19 MB Dwarf galaxies are regarded as cosmological and astrophysical probes on small-scales, thus their discovery and characterization are among the most important goals in the field. Though much effort has been made in surveying Milky Way-mass galaxies and their satellite populations, the sample of satellites around lower-mass hosts is much less understood. I am presenting on the initial results of our ongoing campaign to establish a statistical sample of unresolved dwarf satellites around Large Magellanic Cloud and Small Magellanic Cloud mass (10$^8$ $leq$M$_starleq$ 10$^{10}$ $M_odot$) hosts. As part of the systematic search of the virial volumes around over 30 nearby low-mass hosts (4$<$d$<$10 Mpc), we have identified hundreds of candidate satellite galaxies in the archival DECaLS imaging. The completed sample will provide quantitative constraints for galaxy formation physics and serve as an important benchmark for simulations to try and recover. |
| 32. | Michael Jones, University of Arizona Talk: Building a statistical sample of extremely low mass galaxies July 8, 2024 (9:45 AM) PDF, 1.23 MB The recent discoveries of nearby, extremely low mass galaxies such as Tucana B and Pavo have highlighted the untapped potential of existing wide field surveys in the semi-resolved regime where galaxies are not quite resolved into individual stars. These two galaxies are close in stellar mass, but represent opposite sides of the threshold where cosmic reionization is expected to quench star formation forever. Although established algorithms have been very successful at identifying both fully resolved and unresolved low-mass galaxies, the parameter space in between remains largely unexplored. Pavo was identified in the DESI legacy imaging surveys via a machine learning-aided search for semi-resolved nearby galaxies and is currently the lowest mass star-forming galaxy known in isolation. This search effort has uncovered dozens of additional strong candidates (both quenched and star-forming) in the Legacy Surveys, which we are in the process of following up and confirming as extremely low mass dwarfs beyond the Local Group. I will present the latest results of these efforts, including three new low-mass galaxies within 4 Mpc, and will discuss how applying this technique to LSST will help to maximize its discovery potential for the lowest mass galaxies. Through this approach it will be possible to create the first ever statistical sample of isolated galaxies below a million solar masses, providing a unique opportunity to connect the lowest mass star-forming galaxies to those quenched by reionization and pin down where and how this transition occurs. |
| 33. | Erin Kado-Fong, Yale Talk: Employing Dwarf Galaxies to Assess Star Formation Regulation on Galactic Scales July 9, 2024 (4:20 PM) PDF, 16.38 MB Dwarf galaxies are exceptional probes of star formation physics due to the predominant role that star formation feedback plays in shaping their baryonic structure. Likewise, the physics of star formation regulation must be understood in order to explain the assembly of the low-mass galaxy population, or to use these systems to constrain the nature of dark matter. I will discuss two recent works that quantify the processes that drive, halt, and regulate star formation in dwarfs. In particular, I will (i) show that contrary to what many cosmological simulations require, chemical evolution modeling of low-redshift galaxies implies that star formation in dwarfs is only moderately efficient at driving galactic winds (Kado-Fong et al. 2024a), and (ii) present the existence of a quiescent field dwarf below the self-quenching mass limit, thus demonstrating that interactions between dwarfs can temporarily halt star formation outside the influence of a massive host (Kado-Fong et al. 2024b). These works highlight both the utility of dwarfs in constraining the star formation cycle and the importance of wide-field surveys in cataloging the diversity of low-mass galaxy assembly. Contemporary programs have only just begun to survey the dwarf population beyond the nearby Universe; efforts to constrain star formation regulation via dwarf samples is set to expand even further as LSST unveils increasingly large dwarf galaxy samples out to significant redshifts. |
| 34. | Sergey Koposov, University of Edinburgh Talk: Unravelling the mass spectrum of destroyed dwarf galaxies with the metallicity distribution function July 9, 2024 (9:50 AM) PDF, 0.88 MB Accreted stellar populations are comprised of the remnants of destroyed galaxies, and often dominate the ‘stellar haloes’ of galaxies such as the Milky Way (MW). This ensemble of external contributors is a key indicator of the past assembly history of a galaxy. We introduce a novel statistical method that uses the unbinned metallicity distribution function (MDF) of a stellar population to estimate the mass spectrum of its progenitors. Our model makes use of the well-known mass–metallicity relation of galaxies and assumes Gaussian MDF distributions for individual progenitors: the overall MDF is thus a mixture of MDFs from smaller galaxies. We apply the method to the stellar halo of the MW, as well as the classical MW satellite galaxies. The stellar components of the satellite galaxies have relatively small sample sizes, but we do not find any evidence for accreted populations with L > L host /100. We find that the MW stellar halo has N ∼ 1−3 massive progenitors (L ~ 10^8 Lsun ) within 10 kpc, and likely several hundred progenitors in total. We also test our method on simulations of MW-mass haloes, and find that our method is able to recover the true accreted population within a factor of 2. Future data sets will provide MDFs with orders of magnitude more stars, and this method could be a powerful technique to quantify the accreted populations down to the ultra-faint dwarf mass scale for both the MW and its satellites. |
| 35. | Jiaxuan Li Li, Princeton University Poster: Hedgehog: An Isolated Quiescent Dwarf Galaxy at 2.4 Mpc July 8, 2024 PDF, 4.59 MB It is well-known that almost all isolated dwarf galaxies are actively forming stars. We report the discovery of dw1322m2053 (nicknamed Hedgehog), an isolated quiescent dwarf galaxy at a distance of $2.40pm0.15$ Mpc with a stellar mass of $M_star approx 10^{5.8}, M_odot$. The distance is measured using surface brightness fluctuations with both Legacy Surveys and deep Magellan/IMACS imaging data. Hedgehog is 1.7 Mpc from the nearest galaxy group, Centaurus A, and has no neighboring galaxies within 1 Mpc, making it one of the most isolated quiescent dwarf galaxies at this stellar mass. It has a red optical color, early-type morphology, and shows no UV emission. This indicates that Hedgehog has an old stellar population and no ongoing star formation. Compared with other quiescent dwarfs in the Local Group and Local Volume, Hedgehog appears smaller in size for its luminosity but is consistent with the mass-size relations. Hedgehog might be a backsplash galaxy from the Centaurus A group, but it could also have been quenched in the field by ram pressure stripping in the cosmic web, reionization, or internal processes such as supernova and stellar feedback. Future observations are needed to fully unveil its formation, history, and quenching mechanisms. |
| 36. | |
| 37. | Qing Liu, University of Toronto Poster: Tackling Systematics in Deep Wide-field Imaging Surveys July 8, 2024 Dwarf galaxies are important test particles of galaxy formation theories. A popular approach to searching for dwarf galaxies in deep wide-field surveys is through their diffuse integrated light. At low surface brightness levels, the current detectability and identification of ultra-faint dwarf galaxies are largely limited by systematics including scattered light from the extended wings of the Point Spread Function and interstellar dust grains (the so-called 'Galactic cirrus'), and such systematics will continue to be dominant in LSST. I will introduce approaches developed for handling these systematics based on datasets from Dragonfly, a low surface brightness optimized telescope, which will help us to investigate 'missing' dwarf galaxies hidden in cirrus-riddled sky areas by removing the scattered light contamination. These techniques will help unlock the potential of characterizing low surface brightness phenomena at unprecedented sensitivity by the Vera Rubin Telescope. |
| 38. | Alice Luna, University of Chicago Poster: Metallicity Distribution Function of the Ultra-Faint Dwarf Galaxy Reticulum II July 9, 2024 The metallicity distribution function of stars in ultra-faint dwarf galaxies (UFDs) provides insight into their formation histories. Currently, metallicities are only measured using red-giant branch (RGB) stars in UFDs, greatly limiting the number of stellar metallicities that are possible to measure. Reticulum II is a UFD that currently has only 16 RGB stars with known metallicities. We present Magellan/IMACS spectroscopy of main sequence turn-off stars in Reticulum II, increasing the number of stellar metallicities by ~7x and finding ~40 stars with [Fe/H] < -3. This is the most populated metallicity distribution for any UFD. We fit analytic models of metallicity distributions to this data, which constrains the star formation history of this ancient relic galaxy during the epoch of reionization. We found the metallicity distribution function of Reticulum II to follow a non-Gaussian distribution. |
| 39. | Yifei Luo, University of California Santa Cruz Talk: The Merian Survey: Characterizing dark matter and feedback in star-forming dwarf galaxies with medium-band filters on DECam July 9, 2024 (2:20 PM) PDF, 46.3 MB The Merian survey is an ongoing medium-band imaging survey on the CTIO 4-meter Blanco telescope. With two new medium-band filters on DECam, we expect to detect ~100,000 star-forming dwarf galaxies at z~0.1 in the HSC-SSP wide field (~800 deg^2), aiming to characterize dark matter halo and stellar feedback in dwarf galaxies. The Merian survey will allow us to measure the full dark matter profile of dwarf galaxies via weak gravitational lensing, for the first time. In this talk, I will present how we designed the Merian survey, and discuss the performance by comparing the mock and actual Merian data. I will show the early science results with the Merian Year 1 data release. I will also discuss dwarf lensing with future surveys such as LSST. |
| 40. | Clara Martinez-Vazquez, Gemini Observatory/NSF NOIRLab Poster: The Ancient History of the Local Group told by RR Lyrae Stars July 10, 2024 RR Lyrae stars (RRL) are old (> 10 Gyr) low-mass pulsating variable stars that provide a direct window into the early Universe's conditions. Known for their well-defined and periodic pulsation properties, they serve as excellent standard candles, often used to determine precise distances essential for constraining the orbits and sizes of their host systems. Additionally, the pulsation properties of RRL are linked to their stellar properties, and have been used to derive their metallicity distributions. Based on extensive catalogs of RRL stars, we have investigated the early formation and chemical evolution by deriving metallicity distribution function (MDF) in about 30 dwarf galaxies in diverse environments, the Milky Way, M31, and isolated in the Local Group. Our analysis reveals both intriguing similarities and differences in the pulsation properties of RRL stars across these several dozens of galaxies located in different environments. We find substantial metallicity spreads in certain galaxies (such as Sculptor, Eridanus II, Tucana or Fornax), which reflect the complex evolution of these systems when they were just a few Gyr old. Interestingly, we identify a correlation between the MDFs of RRL and RGB stars that sheds light on the fast or slow star formation history of the host galaxy. Moreover, we have also discovered that the ratio between the number of RRL and RGB stars provides an excellent measure of the old star fraction. These two correlations are powerful tools that will offer new opportunities in the Vera Rubin LSST and ELT era to constrain the star formation history of galaxies within and beyond the Local Group, circumventing the need for deep color-magnitude diagrams and engaging in complex population synthesis modeling. |
| 41. | Kristen McQuinn, STScI; Rutgers University Invited Talk: The Observational Frontiers for Low-Mass Galaxies July 8, 2024 (9:15 AM) |
| 42. | |
| 43. | Francisco J. Mercado, Pomona College Poster: Characterizing environmental effects on galactic sizes in FIREbox July 9, 2024 The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will usher in a new era of astronomy that will unveil the discovery of new galaxies in both isolated regions and around other massive systems. In preparation for this, I utilize FIREbox, a novel, large-volume cosmological simulation based on the FIRE-2 feedback prescription to characterize the morphology and structure of galaxies in different environments. This simulation has the highest dynamic range in the literature, probing scales between ∼ 20 pc to 20 Mpc and, while its volume is modest, FIREbox does not suffer from the limitations that other large-volume simulations face (e.g. unresolved multi-phase gas structure, and reliance on star-formation prescriptions that are calibrated to observations). Furthermore, I use the size-mass relation and the stellar-mass-halo-mass relations as tools to quantify the effects that the cosmic environment has on galactic size and mass. Understanding the connection between these effects and the resulting scaling relations provides us with a unique opportunity to conduct tests that assess our understanding of galaxy formation. |
| 44. | Tim Miller, CIERA Poster: Directly Measuring Distances of Dwarf Galaxies from Multi-Band Images with Simulation Based Inference July 8, 2024 Upcoming wide field surveys from the ground are expected to significantly increase the number of known dwarf galaxies at < 25 Mpc. A critical limiting factor to scientific advancement will be measuring accurate distances to these galaxies. In this talk I will present silkscreen, a framework to infer distances, and stellar population properties, directly from multiband images using simulation based inference (SBI). Traditional techniques such as tip of the red giant branch or surface brightness fluctuations are limited in their widespread applicability; they only work in the resolved and unresolved regimes respectively and do not fully utilize the multi-band information. silkscreen utilizes a convolutional neural network to extract summary statistics from images and a normalizing flow to estimate the posterior of inferred parameters. Silkscreen offers a few key advantages: information from any number of imaging bands to be fully utilized and the Bayesian nature of SBI is crucial as it generates uncertainties and degeneracies for inferred parameters. We apply silkscreen to a sample of galaxies with distances between 1.5 Mpc and 15 Mpc using DeCALS and HSC-SSP imaging. I will show that silkscreen can accurately infer distances based solely on ground based imaging. This initial implementation utilizes specialized simulations and training for each individual galaxy. In the future we plan to train a general model for an entire survey allowing amortized inference where posteriors can be generated for new galaxies in a matter of seconds. Silkscreen will pave the way for reliable and precise distance measurements in the big data regime. |
| 45. | Abby Mintz, Princeton University Poster: Morphology of Hα emission in bright dwarfs using the first Merian Survey data release July 10, 2024 PDF, 7.06 MB Dwarf galaxies are a particularly exciting demographic for testing our current theories of star formation; they are gas-rich, but inefficient at forming stars, bursty, and significantly more impacted by feedback and environment than their more massive counterparts. But due to observational limitations, the recent revolution in the study of spatially resolved star formation in Milky Way analog galaxies has not been extended to dwarfs. I will discuss early science results from the first data release of the optical medium-band Merian Survey – in particular, our use of the medium-band imaging to measure and map Hα emission and star formation in bright dwarfs at 0.06 < z < 0.1. I will present the results of a morphological analysis of the Hα maps and the stellar continuum images, discussing trends with physical parameters. We find that the lowest mass galaxies with the highest SSFR have Hα emission that is consistently centralized and compact, indicating that high SSFRs in low mass galaxies likely result from dynamical instabilities triggered by accretion and interactions. Our results provide insight into the processes that lead to star bursts in low mass galaxies and demonstrate the power of the Merian Survey’s new photometric catalog and imaging. |
| 46. | Sebastian Monzon, Yale University Poster: Constraining the Stellar Halo Mass Relation with Surveys of Satellite Galaxies July 8, 2024 PDF, 1.01 MB The abundance of satellite galaxies around a host is set by the underlying distribution of dark matter substructure in the system. Using SatGen, a sophisticated semi-analytic model, we can accurately predict what these underlying distributions look like according to the standard Lambda-Cold Dark Matter (ΛCDM) cosmology. Our semi-analytic model therefore gives us a powerful link between what is readily observable (galaxies), and what is not (dark matter). We present new machinery to forward model populations of satellite galaxies in a way that properly accounts for cosmic variance. Specifically, we forward model the upcoming third data release of the Satellites Around Galactic Analogs (SAGA) survey. Unlike other observational surveys, SAGA specifically targets host systems that are similar to our own galaxy, the Milky Way. It has been proposed that this host selection criteria combined with a relatively large sample size could help beat down the effects of cosmic variance. We show that even under idealized circumstances, the intrinsic variability in host galaxy formation leads to significant uncertainties. |
| 47. | Aldo Mura Guzmán, Macquarie University / S5 Collaboration Poster: High-Resolution IR Spectroscopy in Sagittarius Stream Stars July 10, 2024 PDF, 4.17 MB Stellar streams are tidally disrupted structures being accreted by our Galaxy, as part of an ongoing cannibalizing process. These stellar streams are therefore integral components of Galaxy evolution and provide crucial information on the formation history of the Milky Way. The Sagittarius dwarf spheroidal galaxy is one of those systems colliding with our Galaxy whose stream stands out as a prominent structure which has been extensively studied. Using high-resolution (R~50000) infrared (IR) spectroscopy, we present the chemical analysis in eight Sagittarius stream stars. These IR observations enable the determination of chemical abundances, including carbon, nitrogen, and oxygen, as well as C isotopic ratios 12C/13C, but also exotic elements such as fluorine, phosphorus, and potassium, from which limited or no observational data is available. With the advent of the new era of mega-telescopes, big surveys, and the colossal amount of data they will bring, what else can we learn? This presentation will explore the potential of high-resolution IR spectroscopy in stellar streams and accreted stars as a complementary dataset to optical observations and the existing data surveys. |
| 48. | Burcin Mutlu-Pakdil, Dartmouth College Talk: The Faint Satellite System of NGC 253: Insights into Low-Density Environments July 9, 2024 (9:30 AM) Local Group satellites have been the primary sample for understanding the astrophysics and cosmological implications of dwarf galaxies. However, there is a danger of ‘overtailoring’ the models to fit local observations. To fully test the ΛCDM model and its underlying astrophysics, studies of satellite systems beyond the Local Group are necessary to sample primary halos with a range of masses, morphologies, and environments. To address this fundamental need, we started PISCeS, a Magellan+Megacam survey to identify dwarfs and other substructures in resolved stellar light around Milky Way (MW)-mass galaxies outside of the Local Group. We recently completed the survey around NGC253 (at 3.5 Mpc), the nearest MW-mass spiral galaxy in an isolated environment, providing us with a unique opportunity to extend the range of environments probed by the existing surveys. We take a deeper look at the faint satellite system of NGC253, and find no convincing evidence for the presence of a plane of satellites surrounding NGC253. We construct its satellite luminosity function, and compare it to those calculated for other Local Volume galaxies. Exploring trends in satellite counts and star-forming fractions among satellite systems, we find relationships with host stellar mass, environment, and morphology, pointing to a complex picture of satellite formation, and a successful model has to reproduce all of these trends. In this talk, I will present these exciting PISCeS results, discuss complementary ongoing efforts, and conclude with a preview of what is possible with "big data" in the coming decade. |
| 49. | Jacob Nibauer, Princeton University Talk: Modeling the Response of Stellar Streams to Substructure with Differentiable Simulations July 10, 2024 (2:00 PM) PDF, 16.88 MB The phase-space density of stellar streams is encoded with information about galactic substructure. Sources of perturbation include both baryonic components (e.g., the galactic bar) and potentially dark matter (e.g., subhalos). Long range aspherical forces due to infalling satellites like the LMC also play a crucial role in shaping some streams. Disentangling the perturbations due to these different gravitational sources has remained a challenging problem in modeling streams. To this end, I will present a new generative model for streams in the presence of substructure, implemented in the Jax library. The model is fully differentiable, enabling the use of methods from perturbation theory that would otherwise be analytically intractable to implement. Leveraging the differentiability of our code, we can efficiently calculate the linear response of a stream to a population of dark matter subhalos, while simultaneously accounting for known baryonic substructures. By using methods from perturbation theory, the strength of each subhalo perturbation can be scaled up and down algebraically, representing a substantial speedup in simulation runtime without a significant loss in accuracy. The model provides a new flexible approach to constrain small-scale galactic substructure, and explore degeneracies between subhalo perturbations and baryonic substructures. |
| 50. | Charlotte Olsen, CUNY City Tech Poster: Discovering the Coevolution of Galaxies and the Multiscale Cosmic Web with Dwarf Galaxy Star Formation Histories in LSST July 9, 2024 PDF, 9.07 MB It is broadly understood that large scale structure can influence galaxy evolution, but it is not as clear how galaxies in less dense environments are shaped by the cosmic web. Dwarf galaxies -- which are particularly sensitive to environment -- serve as excellent probes of the effects of interactions with cosmic structures such as filaments and sheets. Previous studies suggest that the star formation histories (SFHs) of dwarf galaxies in the Local Volume may be sensitive to interactions with smaller filaments and streams over cosmic time. The plentiful data and deep imaging provided by Rubin will allow us to trace the multiscale nature of the cosmic web as never before, and enable the study of how galaxies are influenced over time by cosmic filaments and sheets in their proximity. In anticipation of LSST data we generate synthetic Rubin photometry along with the VISTA VIDEO YJHK bands from the New-Horizon simulations where we reconstruct the SFHs of simulated dwarf galaxies located near filaments. From the SFHs we search for traces of the influence of filament flows in the galaxy SFH and find what these traces reveal about the dynamical history of these surrounding structures. By studying correlations between the SFHs across diverse types of filaments at a given time we can apply this knowledge to actual Rubin observations, thereby discovering how filaments have helped form the galaxies near them. |
| 51. | Xiaowei Ou, MIT Poster: Signatures of tidal disruption of the Hercules ultra-faint dwarf galaxy July 10, 2024 PDF, 0.78 MB The Hercules ultra-faint dwarf galaxy (UFD) has long been hypothesized to be tidally disrupting, yet no conclusive evidence has been found for tidal disruption owing partly to difficulties in identifying Hercules member stars. In this work, we present a homogeneous re-analysis of new and existing observations of Hercules, including the detection of a new potential member star located ~1 degree (~1.7 kpc) west of the center of the system. In addition to measuring the line-of-sight velocity gradient, we compare predictions from dynamical models of stream formation to these observations. We report an updated velocity dispersion measurement based on 28 stars, 1.9+/-0.6 km/sec, which is significantly lower than previous measurements. We find that the line-of-sight velocity gradient is 1.8+/-1.8 km/sec/kpc along the major axis of Hercules, consistent with zero within 1 sigma. Our dynamical models of stream formation, on the other hand, can reproduce the morphology of the Hercules UFD, specifically the misalignment between the elongation and the orbital motion direction. Additionally, these dynamical models indicate that any radial velocity gradient from tidal disruption would be too small, 0.00+/-0.9 km/sec/kpc, to be detectable with current sample sizes. Combined with our analysis of the tidal radius evolution of the system as a function of its orbital phase, we argue that it is likely that Hercules is indeed currently undergoing tidal disruption in its extended stellar halo with a line-of-sight velocity gradient too small to be detected with current observational datasets. |
| 52. | |
| 53. | Nondh Panithanpaisal, Carnegie Observatories & Caltech Poster: A Slingshot Effect: The Origin of Backsplash Galaxies Around Milky Way-mass Hosts in FIRE July 8, 2024 Backsplash galaxies are galaxies that are beyond the virial radius of a more massive host at z=0, but have been within the host halo in the past. Their existence was predicted and observed mostly around galaxy clusters. In this work, we extend the prediction of a backsplash galaxy population down to those around a Milky Way-mass halo ($M_{200m}sim10^{12}Msun$). Using the suite of FIRE cosmological zoom-in simulations of galaxy formation, we find evidence that the slingshot effect from a past encounter with a massive merger is one of the mechanisms that create backsplash halos around Milky Way-mass galaxies. These halos can be excited into a higher-energy orbit from the energy exchange with the massive merger. For all halos within 750 kpc at z=0, the backsplash halos occupy a different region in phase space, compared to the field halos, with a net positive radial velocity providing the strongest support of the backsplash nature. Due to their past orbits inside the host, backsplash halos have been significantly disrupted, mostly in dark matter, with a small fraction of the halos having a disrupted stellar component as well. To accurately model galaxy properties and their internal dynamics, it is crucial to distinguish between backsplash and field galaxies. Our findings have implications for modeling faint dwarf galaxies at or beyond the Milky Way's virial radius, many of which could be backsplash galaxies due to the presence of the Large Magellanic Cloud, and they can potentially be detected by upcoming surveys such as the Rubin Observatory's LSST. |
| 54. | Yue Pan, Princeton University Poster: Quenching in dwarf galaxies July 9, 2024 PDF, 1.32 MB Despite recent progress in understanding dwarf galaxies, the complex interplay of internal and external processes affecting star formation and quenching in these systems remains unresolved. I will present two studies, spanning theoretical and observational approaches, that offer a comprehensive view of the effects of bursty star formation on galaxy scaling relations and the structural diversity of satellite galaxies orbiting Milky Way (MW) analogs. First, I will discuss my theoretical work, investigating the impact of bursty star formation on dwarf galaxies by using the exttt{GRUMPY} galaxy formation model. We explore the influence of stochastic star formation rates (SFRs) on several scaling relations such as SFR--stellar mass, stellar mass--gas mass, and stellar mass--metallicity. Our model shows that increased SFR stochasticity aligns the scatter in these relations with that observed in nearby dwarf galaxies. Particularly, brighter dwarf galaxies $(M_V < -12)$ exhibit increased scatter in the colour--magnitude distribution (CMD) to levels seen in observations, although fainter galaxies still show less scatter due to their predominantly old stellar populations and declining SFRs over the past 10 Gyrs. We also investigate the possibility that scatter in CMD could be linked to metallicity variations, though this leads to an overestimated scatter in the metallicity--mass relation. Then, I will describe preliminary results from the Merian survey DR1, examining star-forming satellite galaxies around MW analogs. With approximately 5000 MW analogs at redshifts 0.06 < z < 0.1, we will study their satellites’ stellar mass functions, radial distributions, and structures. This observational dataset will also be used to examine the frequency of LMC/SMC analogs around MW-like hosts and assess whether such configurations are common or unique among similar mass galaxies. |
| 55. | Ava Polzin, The University of Chicago Poster: Star formation in low-metallicity dwarf galaxies July 9, 2024 PDF, 2.7 MB I will present a new, simple model to describe the fraction of molecular hydrogen gas in low metallicity galaxies, which can be applied to both local, low mass dwarf galaxies and galaxies at high redshift where the global metallicity is lower. We find that the star formation rate is not directly tied to the amount of molecular hydrogen in low metallicity galaxies, implying that star formation occurs in cold neutral gas generally, rather than molecular gas specifically. This suggests that molecular hydrogen-based star formation prescriptions miss this reservoir of star-forming material by default. I will discuss the implications of this additional reservoir for low metallicity galaxy evolution. I will also discuss self-regulation in this regime, pointing to evidence for a turbulence-regulated model of star formation efficiency. |
| 56. | Claire Riggs, Rutgers, the State University of New Jersey Poster: Using Cosmological Simulations to Explore the Stellar Age Gradients of Dwarf Galaxies July 9, 2024 PDF, 3.08 MB Dwarf galaxies across a large range of masses and environments tend to have their younger stars near their centers and their oldest stars near the outskirts, which is the exact opposite of the better-understood "inside-out" stellar age gradients observed in large, Milky Way-sized galaxies. While dwarf galaxies’ stellar age gradients suggest an “outside-in” formation mechanism, we show that dwarf galaxies actually form inside-out, but a variety of mechanisms including dark matter core creation pushes the stars out over time, creating the outside-in stellar gradient observed in dwarf galaxies. Our sample of 73 simulated galaxies spans a stellar mass range of $10^6-10^9$ M$_odot$ and contains halos in both satellite and field environments. We look at trends of star formation history, dark matter core creation, and merger history in order to determine how these processes interact with properties like mass and environment to create the stellar age gradients we observe in dwarfs. |
| 57. | Clayton Robertson, University of Louisville Poster: Ground- and Space-Based Dust Observations of VV,191 Overlapping Galaxy Pair July 8, 2024 PDF, 9.59 MB Extragalactic dust attenuation has fundamentally relied on the Balmer decrement (H$alpha$/H$eta$) for decades. The ratio is a reliable spectroscopic tool for deriving the dust properties of galaxies that determine galactic properties such as star formation rate (SFR), metallicity, spectral energy distribution (SED) models, and more. Here, we extit{independently} measure both the attenuation and Balmer decrement of an optimal occulting (overlapping) galaxy pair: VV,191 (z = 0.0514 and z = 0.0513 for the spiral foreground, VV,191b and background elliptical galaxy, VV,191a, respectively). We use observations from the Hubble Space Telescope and the James Webb Space Telescope using NIRCam on 2 July 2022 as part of the PEARLS GTO program (1176) to directly derive attenuation ($A_{V}$) measurements. The George and Cynthia Mitchell Spectrograph (GCMS)/Visible Integral-field Replicable Unit Spectrograph (VIRUS-P) of the McDonald Observatory from the University of Texas provides integral field unit (IFU) observations of VV,191 with bandpass that covers the two Balmer lines (H$alpha$ and H$eta$) for the Balmer decrement. We independently compute $A_{V}$ and H$alpha$/H$eta$ for direct comparison to the literature that dictates the Balmer decrement's influence on $A_{V}$. |
| 58. | Katy Rodriguez Wimberly, Cal State San Bernardino Poster: Chemical Abundances in our UFDs: Hydrus I and Willman 1 July 9, 2024 PDF, 1.34 MB The Early Universe continues to be largely elusive — with many questions unanswered involving the origins, evolutionary histories, and compositional characteristics of the smallest, most ancient galaxies — ultra–faint dwarfs (UFDs). While the counts and kinematics of observed UFDs are roughly accommodated in simulations and semi-analytical models, reproducing their metallicities has remained a persistent tension between observations and theory. Simulations predict a strong scaling between M∗ and [Fe/H] that is understood as a result of star formation proceeding mostly in-situ and polluting the interstellar medium proportionally to the number of stars formed. Instead, observations suggest that there is a “flattening” or plateau on the scale of ultrafaints, hinting at a decoupling between the stellar mass and the amount of metals produced. This disagreement has profound implications: Are UFDs just tidally stripped remnants of more massive galaxies? Is there a minimum mass threshold for galaxy formation? Are many ultrafaints actually stellar clusters, indicating a lack of understanding of dark matter halo occupation fractions? Metallicity and detailed chemical abundance measurements can assist in sorting these possibilities. Here I will present work in progress detailing the chemical abundances in 2 ultrafaint dwarf galaxies in the metallicity plateau: Hydrus I and Willman 1. |
| 59. | Dilys Ruan, Rutgers University Poster: The Baryonic Tully Fisher Relationship in Simulated Dwarf Galaxies July 9, 2024 PDF, 1.93 MB The baryonic Tully-Fisher (BTF) relationship provides a measurement of the fundamental relation between baryonic mass and dark matter mass (measured by maximum rotation velocity) for galaxies. At the lower mass end, the BTF relationship is poorly constrained due to small samples and difficulty in connecting the galaxy’s gas kinematics to its dark matter halo. Simulations can help us understand this connection and interpret observations to come. As LSST discovers more dwarf galaxies, the WALLABY survey can follow up to understand their properties down to HI velocity ~30 km/s, which is within the velocity range where simulations and observations diverge in the BTF relation. We explore HI gas kinematics for a large sample of simulated dwarfs in the Marvel and Marvelous Merian hydrodynamic simulation suites, with stellar masses ranging from ~10^6 to 10^9 Msol. We find that the baryonic content of the simulated dwarfs is in good agreement with observed dwarf galaxies. We determine the sample’s HI linewidths (W10, W20, and W50) and compare them as proxies for the dark matter halo’s max rotation velocity. We assess the radial extent probed by HI in dwarfs and how that impacts the resulting BTF. |
| 60. | Pradyumna Sadhu, University of California, Riverside Poster: Probing the Faint Universe with Vera Rubin Observatory: the satellite mass function of Virgo-like clusters in LCDM from ultrafaint dwarfs to giant ellipticals July 8, 2024 PDF, 4.35 MB Current cosmological simulations lack the resolution to make reliable predictions for faint and ultra-faint dwarf satellites, which will become crucial test of the LCDM model in the upcoming era of the Vera Rubin Observatory. To this end, we implement a semi-analytical model based on higher-resolution simulations to complement the predictions of the TNG50 cosmological numerical simulations. We focus on 3 clusters with virial masses ~1e14 Msun, comparable to Virgo and Fornax, and characterize their satellite population from ultrafaint dwarfs to massive elliptical galaxies. We find that under the assumption of cuspy dark matter halos such as NFW profiles, the majority of all satellite galaxies survive within cluster environments, expecting 10-50 thousand luminous satellites within the virial radius of such clusters. This is contrary to the results directly from the simulation where satellites get merged artificially due to poor numerical resolution. We characterize the radial distribution of luminous and dark remnants highlighting the consequences for the modeling of gravitational lenses. |
| 61. | David Sand, University of Arizona Talk: Quenched Ultra-faint Dwarf Galaxies in the Field and Low-Density Environments July 8, 2024 (4:20 PM) PDF, 5.9 MB Quenched, field dwarfs in the ultra-faint dwarf galaxy regime may cease forming stars not because of any interaction with a larger galaxy but due to reionization or other internal mechanisms, such as supernova feedback. The discovery of such systems would provide a strong verification of galaxy formation models on small scales. Here we first present the latest results on Tucana B, a unique ultra-faint (D~1.4 Mpc; L=50,000 L_sun), which likely never had an encounter with the Milky Way's hot halo or tidal field, yet it only display an old (~13 Gyr), metal poor ([Fe/H]=-2) stellar population, and it lacks any HI gas with which to make new stars -- it is quenched. JWST observations down to the oldest main sequence turnoff (Cycle 3) will be a definitive test of the role that reionization plays, identifying whether early star formation stopped around the reionization epoch, or continued up until more recent times, as is seen in more massive field dwarfs. We will also discuss a new set of ultra-faint dwarf galaxy satellites around NGC300 (LMC-mass; D~2 Mpc), which will also be a unique test for the role of reionization in the smallest galaxies. With these systems in hand, we discuss next steps, including techniques for identifying other faint dwarfs in the field with LSST and the Roman Space Telescope. |
| 62. | Alessandro Savino, U.C. Berkeley Talk: The Star Formation History of the M31 Satellite System July 8, 2024 (4:00 PM) PDF, 11.99 MB Within the past decades, the exquisite observational characterization of the Milky Way (MW) satellite population has progressively anchored the framework of low-mass galaxy formation and small-scale structure growth in the Universe. However, the MW halo is a single environment, leading to questions of whether the MW satellites are broadly representative of L* galactic ecosystems. I will present new results from the HST Treasury survey of the M31 satellites, which has measured lifetime star formation histories (SFHs) of virtually all known dwarf galaxies around M31, from ultra-faints (Mv= -6.0) to dwarf ellipticals (Mv= -16.8). I will compare the SFHs of the M31 satellites to those of the MW, highlighting similarities but also differences that might be linked to the different accretion histories of their hosts. I will also focus on the 6 ultra-faint dwarfs in our sample, showing how their star formation history paints a more nuanced picture of how reionization affects galaxy formation in low-mass halos. I will connect open questions from these results to future galaxy discoveries by Rubin, both within and outside the Local Group. |
| 63. | Katherine Sharpe, University of California, Berkeley Poster: The First Alpha Abundances in Isolated Dwarf Galaxies Using JWST Spectroscopy July 9, 2024 PDF, 27.63 MB I will present initial results from a JWST Cycle 2 program that is obtaining spectroscopy of ~200 resolved stars in three isolated Local Group dwarf galaxies: Leo A, Tucana, and IC 1613. These targets were selected as representative young, ancient, and intermediate age systems, respectively, which should have correspondingly diverse chemical enrichment histories. The majority of dwarf galaxy metallicities and abundances today come from the easily accessible Milky Way satellites. However, JWST’s exquisite sensitivity and superior angular resolution makes it possible to measure large sets of [alpha/Fe] in galaxies at the edge of the Local Group and beyond, enabling studies of chemical enrichment in the absence of the environmental processes that affect satellite galaxies. Here, I will summarize our program and highlight some of the unique technical challenges posed by JWST’s spectroscopic set-up. I will present initial results (e.g., some of the first stellar spectra acquired by JWST at large distances, stellar chemistry in isolated dwarf galaxies) and preview prospects for the use of JWST in acquiring stellar abundance measurements outside of the Local Group. |
| 64. | Zili Shen, Yale University Talk: Nearby ultra-diffuse galaxies in the Dragonfly Ultrawide Survey July 8, 2024 (2:20 PM) PDF, 16.19 MB Existing galaxy surveys could be missing a population of apparently large, diffuse, quiescent galaxies due to their extremely low surface brightness. This population includes nearby Ultra-diffuse Galaxies (UDGs) which are dwarf galaxies that are at least 1.5 kpc in size. They are difficult to characterize because most known UDGs are in clusters and are too distant for detailed follow-up. Theory papers have predicted a dozen of UDGs within 2.5 Mpc (~2 within the SDSS footprint), which would make their apparent sizes several arcminutes. The Dragonfly Telephoto Array is uniquely optimized for imaging this type of large, low surface brightness objects in integrated light. With its 6 sq. deg. field of view and a relatively unobstructed light path, Dragonfly has unprecedented sensitivity to low surface brightness features and exquisite control over background systematics. We have recently completed the Dragonfly Ultrawide Survey (DFUWS), which covers the entire SDSS footprint in g- and r-band imaging. The 30-minute integration times yield surface brightness limits below 29 mag/arcsec^2 on 1'x1' scales. From 3000 sq. deg. of DFUWS early internal release data, we identified eleven large, low-surface-brightness galaxies and obtained Keck/KCWI spectroscopy for their radial velocities. This sample of quiescent, large, diffuse galaxies range between 12-25 Mpc in distance, and between 15" and 30" in apparent size. As our search for arcminute size UDGs continues, LSST will provide a complementary dataset in the Southern sky and cover a much wider area. We hope to explore the synergies between Dragonfly and LSST and expand the search of nearby UDGs with future datasets. |
| 65. | Josh Simon, Carnegie Observatories Invited Talk: Spectroscopic Frontiers and Observational Challenges in Studying Dwarf Galaxies July 8, 2024 (3:30 PM) PDF, 18.49 MB |
| 66. | Simon Smith, University of Victoria Talk: Ursa Major III/UNIONS 1, the faintest known satellite of the Milky Way July 10, 2024 (9:30 AM) PDF, 20.16 MB In this work, I will present the faintest known satellite of the Milky Way, Ursa Major III/UNIONS 1, named as such due to its nature as a dark matter-dominated dwarf galaxy or a dark matter-free star cluster being as yet unknown. Ursa Major III/UNIONS 1 is estimated to have a total V-band magnitude of +2.2 mag, a total stellar mass of 16 solar masses, and only about 60 total stars. Gaia proper motions and follow-up radial velocities from Keck/DEIMOS confirmed 11 member stars brighter than G ~ 21 mag, from which the velocity dispersion was measured to be 3.7 km/s. Taken at face value, this would imply a dynamical mass-to-light ratio of ~6500 within the half-light radius of 3 pc and the presence of a massive dark matter halo shadowing the faintest known coherent Milky Way satellite. However, the current radial velocity uncertainties (> 1 km/s), the unknown presence of binary stars, and the assumption of dynamical equilibrium all call into question whether the measured velocity dispersion is indicative of the underlying gravitational potential. This presentation will detail the discovery of Ursa Major III/UNIONS 1 and discuss additional on-going work which seeks to address these listed caveats and further constrain the dynamical mass of this extraordinary object that pushes the mass function of Milky Way satellites to 10s of solar masses and may extended the definition of ‘galaxy’ to length scales of parsecs. |
| 67. | Tjitske Starkenburg, Northwestern University Talk: Globular cluster stellar streams beyond the Milky Way July 8, 2024 (2:00 PM) PDF, 10.41 MB Stellar streams from tidally stripped globular clusters are one of the most sensitive tracers of their surrounding gravitational potential. Streams from clusters are thin and dynamically relatively cold, and any perturbation of stars in the stream thus leads to potentially observable effects. For example, gaps and overdensities along the stream can arise from interactions with low-mass dark matter subhalos and thus provide constraints on the nature of dark matter. Larger-scale perturbations of the host potential can lead to inconsistencies between the orbital track and the stellar kinematics as well as morphological changes. While globular cluster stellar streams have so far only been observed in the Milky Way, upcoming facilities such as the Nancy Grace Roman Telescope and the Vera Rubin Observatory can greatly increase their number, both within the Milky Way and in external galaxies. I will present synthetic observations for Roman and Rubin of thin stellar streams and gaps in M31 and other galaxies in the local universe in resolved stars and integrated light, and show that streams and their own substructure will be observable out to a few Mpc. Additionally, I will show how major mergers can affect the morphology, structure, orbits, and kinematics of pre-existing globular cluster stellar streams. These results provide key insights to interpret a more complete sample of stellar streams in multiple galaxy environments, and to connect the streams to their globular cluster origin and their host galaxy’s formation history. |
| 68. | Chin Yi Tan, University of Chicago Poster: Constraints of Mixed Warm Dark Matter from Milky Way Satellite Galaxies July 8, 2024 Milky Way satellite galaxies include some of the oldest, faintest, and most dark matter dominated stellar systems known. By performing a rigorous census of Milky Way satellite galaxies that includes detailed estimates of current observational sensitivities, we are able to extend previous analyses to present novel constraints on a mixed warm dark matter (mWDM) scenario that contains both warm and cold dark matter components. We use the semi-analytical model SASHIMI to obtain the mWDM subhalo suppression function from the mWDM matter power spectrum as a function of WDM particle mass and fractional abundance. We then “paint” satellite galaxies onto simulated subhalos using a galaxy-halo connection model and compare the resulting satellite population to the observed satellite population from the Dark Energy Survey and Pan-STARRS1 to obtain constraints on the fractional abundance of warm dark matter as a function of the WDM particle mass. In addition to generic thermal mWDM, we also constrain mixed cold dark matter and sterile neutrino models produced by the Shi-Fuller mechanism. We also briefly describe the potential of future surveys to increase the completeness of the Milky Way satellite census and tighten constraints on mixed dark matter scenarios. |
| 69. | Yimeng Tang, University of California, Santa Cruz Poster: Observational constraints on the formation of dark-matter deficient galaxies from morphologies, stellar populations and globular clusters July 9, 2024 PDF, 2.05 MB Widespread attention has focused recently on nearby dwarf galaxies deficient in dark matter (DM), particularly DF2 and DF4 near the massive galaxy NGC 1052. The two leading formation scenarios are tidal stripping and a "bullet-dwarf" high-speed collision -- both of which are predicted to occur in cosmological simulations. The bullet dwarf scenario represents a novel pathway for galaxy formation, and potentially provides constraints on the cross-section of DM and alternative theories to cold DM. This is the only scenario so far to provide a natural explanation for two other unusual properties of DF2 and DF4: their peculiar globular cluster systems, and their apparent association with a large linear substructure or "trail". Here we present a study of stellar populations and morphologies of dwarfs in the NGC 1052 group, both on and off the trail, to provide novel constraints on the formation scenarios. We also analyze spectroscopy and Hubble Space Telescope imaging of a third galaxy with a peculiar globular cluster system, to determine if it is a candidate for being deficient in DM. This work represents a pathfinder to identifying more of these intriguing galaxies in the upcoming deep, wide-field surveys including LSST. |
| 70. | Pierre Thibodeaux, University of Chicago Poster: Simulating Dwarf Galaxy Stellar Kinematic Measurements July 8, 2024 Ultra-faint dwarf galaxies (UFDs) are the lowest-mass, lowest-luminosity satellite galaxies of the Milky Way. In addition to being the most metal-poor and the least chemically evolved galaxies known, they are the most dark matter-dominated systems we can observe. The next generation of photometric surveys (DELVE, LSST, Roman) will enable the discovery of large numbers of UFD candidates, giving us a better understanding of the properties of dark matter. Spectroscopic observations are necessary to constrain the dark matter content of these systems and distinguish whether these candidates are actual dark-matter-dominated UFDs or dark-matter-deficient star clusters. We present projections for the ability to measure velocity dispersions in ultra-compact UFDs with current and future spectroscopic facilities. We simulate line-of-sight velocity observations of stellar populations from a dynamical model, using instrumental data to apply realistic observation uncertainties. We also present projections for the measurement of J-factor and J-factor uncertainties with current and future spectroscopic facilities. The ability to precisely measure the J-factor of UFDs is important for constraining the dark matter annihilation cross section, which will elucidate the particle nature of dark matter. This study informs the design of future telescopes, instruments, and their observational programs. |
| 71. | Erik Tollerud, Space Telescope Science Institute Poster: COS-SAGA: A 3-sightline Probe of a Local Group Analog's CGM July 9, 2024 The flow of gas into and out of galaxies is crucial to understanding how galaxies quench. However, the connection between the circumgalactic medium (CGM) and satellite galaxies is poorly understood. In this poster, I will describe the COS-SAGA survey, targeting quasars around local (d < 40 Mpc ) Milky Way-like galaxies with known satellites population from the Satellites Around Galactic Analogs survey (SAGA, Geha et al. 2017, Mao et al. 2021). In this poster we describe a particular system from COS-SAGA that has 3 different sightlines, as well as a single satellite, leading to simpler interpretation then more complex or less data-rich systems. We describe both the observations themselves, as well as a modeling approach to mapping theoretical histories of the system to the QSO observations. This system thus serves as both a fascinating data point in its own right and as a test case for future missions like HWO that will blow the door open on understanding the CGM and its connection both to host galaxies and their attendant satellites. |
| 72. | Samantha Usman, UChicago Poster: The Relationship Between Mass and Multiple Populations in Globular Clusters and Their Streams July 10, 2024 Globular clusters are often considered the ideal stellar system for comparison: they form at the same time and from the same cloud of gas, meaning each cluster is a pristine set of hundreds of thousands or millions stars that are the same age with the same composition. Except there is a complication: despite forming out of the same material, the stars in globular clusters do not have the same composition. They contain multiple populations: distinct groups of stars within a single cluster that exhibit variations in their chemical composition, particularly in elements like sodium, magnesium, aluminum and oxygen. These chemical patterns were first identified more than fifty years ago, but the mechanism for this enrichment is not well understood. There is one hint to understanding this phenomenon: more massive globular clusters have proportionally more enriched stars than less massive ones. We probe this relationship by observing globular clusters and their disrupted remnants called stellar streams. We quantify the composition of the stars in these stellar systems using spectroscopy from the Magellan telescope. We find that globular clusters need to have a mass of 10^5 solar masses at its time of formation to have multiple populations, while clusters that form with a mass of 10^6 solar masses have approximately 75% of their stars enriched. |
| 73. | Vaishnav Venugopal Rao, University of Michigan, Department of Astronomy Poster: Finding Ultra-Faint Dwarf Galaxies in M81's Stellar Halo July 8, 2024 It has long been known that galaxies form hierarchically by accreting small stellar systems over a long period of time. This understanding of small-scale cosmology is built on the discovery and characterization of the faint and ultra-faint dwarf satellite galaxies that populate stellar halos in the Local Group. In order to check if our insights from Local Group observations generalize to higher redshifts, it is essential to use resolved star techniques to discover faint satellites in nearby galaxies. We present here a search for ultra-faint galaxies in the M81 group using deep ground-based resolved star datasets from Subaru’s Hyper Suprime Cam. Compared to stars identified in GHOSTS fields, morphology and stellar locus-based star selection methods allow us to recover approximately 60% of all stellar sources with a background galaxy contamination of about 30% at TRGB magnitudes. Red giant branch (RGB) stars chosen up to 2 magnitudes below the TRGB allow us to generate a clean map of the stellar halo out to approximately 115 kpc from the center of M81. Using kernel density estimation methods to find significant clusterings of old, metal-poor RGB stars, we recover all but two known dwarf satellites and detect many more marginal candidate ultra-faint dwarf galaxies whose CMDs correspond to stellar populations at M81 distances. The analysis we present also serves as a template for satellite searches using upcoming Rubin Observatory datasets, and the results hint at the immense scientific promise of resolved star surveys that the Roman Space Telescope would conduct around nearby galaxies. |
| 74. | Kathy Vivas, NOIRLab Talk: Is Crater II disrupting? July 10, 2024 (4:00 PM) PDF, 11.46 MB Crater II is a fascinating galaxy. It is the fifth largest galaxy among the satellites of the Milky Way but significantly less luminous than other galaxies of its size. Both its very low velocity dispersion and its fiducial orbit, which brings it as close as 33 kpc from the Galactic center at perihelion every ∼ 2 Gyr, predict that this ultra-diffuse galaxy must be disrupting by the tidal forces of the Milky Way. The search for tidal debris around Crater II is however a challenging task due to its very large size, large distance (116 kpc), and very low density, which implies large contamination by foreground stars and faint background galaxies. We describe here a 27 sq deg survey made with the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile, designed to uncover an extended population around Crater II. In this survey we use RR Lyrae variable stars as tracers of the (old) population of Crater II to infer its morphology, metallicity dispersion, and distance, a crucial parameter to derive accurately the orbit of Crater II and determine its close passages to the Milky Way. |
| 75. | Yunchong (Richie) Wang, Stanford University Poster: Towards a Unified Model of Dwarf Galaxy Formation and Evolution with UniverseMachine July 9, 2024 PDF, 1.44 MB Dwarf galaxies provide rich constraints on galaxy formation, reionization, and the nature of dark matter. However, flexible models of their star formation histories in a cosmological context are lacking. We introduce a novel framework for connecting dwarf galaxy dark matter assemblies and star formation histories based on the empirical model UniverseMachine (UM). Our framework is flexible, such that it can be simultaneously constrained by observations over a wide range of galaxy masses, environments, and redshifts. We constrain our model using observations of satellite galaxies around 101 Milky Way analogs, from the Satellite Around Galactic Analogs (SAGA) survey, and field galaxies from SDSS. We find that a strong correlation between halo stripping and satellite quenching is required to reconcile the large difference between satellite and field galaxy quenched fractions at low stellar masses. This framework also enables us to jointly model bright dwarf galaxies with ultra-faint dwarfs in the Local Group (LG) anchored on dark matter simulations with embedded disk potentials for baryonic disruption, providing a link between the high redshift and very local universe. I will also discuss ongoing work improving subhalo modeling with reionization quenching and conformity. |
| 76. | Kaitlin Webber, Texas A&M University Poster: Abundance Analysis of the Turranburra and WillkaYaku Stellar Streams July 10, 2024 In recent years,large photometric surveys such as the Dark Energy Survey (DES) have discovered a number of substructures in and around the Milky Way. Many of the substructures discovered in the Milky Way are stellar streams, remnants of tidally stripped dwarf galaxies or globular clusters. Studying these systems gives an insight into the formation and chemical evolution of our Galaxy. The Southern Stellar Stream Spectroscopic Survey (S5) has performed spectroscopic follow-up on these streams, including the Turranburra and Willka Yaku streams. I will present the results of a detailed abundance analysis of the three brightest members in both Turranburra and Willka Yaku which are believed to be remnants of a dwarf galaxy and a globular cluster, respectively. I will discuss the chemical signatures of the two streams, displayed by the abundances derived for 26 elements, including an enhancement in neutron-capture elements. |
| 77. | Dan Weisz, UC Berkeley Talk: The Low-Mass Galaxy Frontier with the UltraViolet Explorer July 8, 2024 (10:05 AM) PDF, 17.39 MB The Ultraviolet Explorer (UVEX) is a recently selected NASA MIDEX mission that will provide deep UV imaging and UV spectroscopy across the entire sky. A main science driver of UVEX is to define a new frontier for the study of nearby (D<1500 Mpc; z<0.3) star-forming low-mass, low-metallicity (LMLZ; Mstar< 10^9 Msun) galaxies. In tandem with optical/IR wide-area surveys (e.g., LSST, Euclid, UNIONS), UVEX will (i) uncover the millions of LMLZ galaxies that are theoretically predicted to exist in the l local Universe (z<0.3), while only thousands are currently known, providing large-scale tests of galaxy formation, abundance matching, etc. in the field; (ii) provide precise photometric metallicities for ~10^8 stars throughout the entire MW halo, which will enable a range of studies from extremely metal-poor stars to identifying faint sub-structures; (iii) undertake UV spectroscopic and time series surveys of >1000 hot, massive single and binary stars in the LMC, SMC, and other low-metallicity star-forming dwarf galaxies. In this talk, I will introduce the UVEX survey and describe its science aims. I will highlight areas of strong synergy with LSST and solicit input on UVEX data products that will be useful to the community. |
| 78. | Zijing Xue, University of Southern California, Carnegie Observatories Poster: Probing substructures of the Jet stream with deep u-band photometry July 10, 2024 PDF, 13.92 MB Thin, dynamically cold stellar streams are powerful probes of the presence of small-scale dark matter subhalos in the Milky Way gravitational potential. Previous studies of substructures present in such streams have been focused on streams closer to the Milky Way disk, which causes noise in the dark matter signal. We take on one particular case, the Jet stream, which harbors a ~4° under-density and indicators of a possible spur off its main track analogous to that of GD-1. The stream also lies clear from the Milky Way disk, suggesting a higher likelihood of detecting past encounters of dark matter subhalos. We obtain new deep (~25.5 mag) photometry in the u, g, and r bands with the Magellan Megacam, and run analysis of the images with legacypipe based on the Tractor framework. Combining with the delicate astrometry from Gaia Data Release 3, we derive a catalog of highly likely members of the Jet stream, and with further modeling of the stream morphology, present an analysis of the substructures our high-resolution map presents. Our study matches the photometric depth expected from the future data collected by LSST, the more filters and higher precision phase space measurements of which should further improve the dynamical modeling and expand the dataset to dozens of similar cold stellar streams. |
| 79. | Eric Zhang, University of California, Riverside Poster: Bursty Star Formation in Dwarfs is Sensitive to Numerical Choices in Supernova Feedback Models July 9, 2024 Simulations of galaxy formation are mostly unable to resolve the energy-conserving phase of individual supernova events, having to resort to subgrid models to distribute the energy and momentum resulting from stellar feedback. However, the properties of these simulated galaxies, including the morphology, stellar mass formed and the burstiness of the star formation history, are highly sensitive to numerical choices in these subgrid models. Using the SMUGGLE stellar feedback model, we run idealized simulations of a $M_{ m vir} sim 10^{10} , msun$ dwarf galaxy, a regime where most simulation codes predict significant burstiness in star formation histories, which are associated with the formation of dark matter cores. We find that by varying only the directional distribution of momentum imparted from supernovae to the surrounding gas, while holding the total momentum per supernova constant, bursty star formation may be amplified or completely suppressed, and the total stellar mass formed can vary by as much as a factor of $sim 3$. In particular, when momentum is primarily directed perpendicular to the gas disk, less bursty and lower overall star formation rates result, yielding less gas turbulence, more disky morphologies and retention of cuspy dark matter density profiles. Further understanding of complexities in the coupling of stellar feedback into an inhomogeneous gas media are needed to make robust predictions for stellar morphologies and dark matter core formation in dwarfs that are independent of the numerical choices in the baryonic treatment. |
| Overview | Participants | Program | Presentations | KICP |
