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1. Systematically Measuring Ultradiffuse Galaxies (SMUDGes). IV. Ultradiffuse Satellites of Milky Way Analogs

   https://doi.org/10.3847/1538-3881/acf4f4  

   Goto, Hina; Zaritsky, Dennis; Karunakaran, Ananthan; Donnerstein, Richard; Sand, David J (October 2023, The Astronomical Journal)

   Abstract To better understand the formation of large, low-surface-brightness galaxies, we measure the correlation function between ultradiffuse galaxy (UDG) candidates and Milky Way analogs (MWAs). We find that: (1) the projected radial distribution of UDG satellites (projected surface density ∝r^{−0.84±0.06}) is consistent with that of normal satellite galaxies; (2) the number of UDG satellites per MWA (S_UDG) is ∼0.5 ± 0.1 over projected radii from 20 to 250 kpc and −17 <M_r< −13.5; (3)S_UDGis consistent with a linear extrapolation of the relationship between the number of UDGs per halo versus halo mass obtained over galaxy group and cluster scales; (4) red UDG satellites dominate the population of UDG satellites (∼80%); (5) over the range of satellite magnitudes studied, UDG satellites comprise ∼10% of the satellite galaxy population of MWAs; and (6) a significant fraction of these (∼13%) have estimated total masses >10^10.9M_⊙or, equivalently, at least half the halo mass of the LMC, and populate a large fraction (∼18%) of the expected subhalos down to these masses. All of these results suggest a close association between the overall low-mass galaxy population and UDGs, which we interpret as favoring models where UDG formation principally occurs within the general context of low-mass galaxy formation over models invoking more exotic physical processes specifically invoked to form UDGs. 

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2. Effects of Galactic Environment on Size and Dark Matter Content in Low-mass Galaxies

   https://doi.org/10.3847/1538-4357/adbf07  

   Mercado, Francisco J; Moreno, Jorge; Feldmann, Robert; Zeender, Marckie; Benavides, José A; Piotrowska, Joanna M; Klein, Courtney; Wheeler, Coral; Necib, Lina; Bullock, James S; et al (April 2025, The Astrophysical Journal)

   Abstract We utilize the cosmological volume simulation FIREbox to investigate how a galaxy’s environment influences its size and dark matter content. Our study focuses on approximately 1200 galaxies (886 central and 332 satellite halos) in the low-mass regime, with stellar masses between 10⁶and 10⁹M_⊙. We analyze the size–mass relation (r₅₀–M_⋆), the inner dark matter mass–stellar mass ( $M_{\mathrm{DM}}^{50}$–M_⋆) relation, and the halo mass–stellar mass (M_halo–M_⋆) relation. At fixed stellar mass, we find that galaxies experiencing stronger tidal influences, indicated by higher Perturbation Indices (PI > 1) are generally larger and have lower halo masses relative to their counterparts with lower Perturbation Indices (PI < 1). Applying a Random Forest regression model, we show that both the environment (PI) and halo mass (M_halo) are significant predictors of a galaxy’s relative size and dark matter content. Notably, becauseM_halois also strongly affected by the environment, our findings indicate that environmental conditions not only influence galactic sizes and relative inner dark matter content directly, but also indirectly, through their impact on halo mass. Our results highlight a critical interplay between environmental factors and halo mass in shaping galaxy properties, affirming the environment as a fundamental driver in galaxy formation and evolution. 

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3. Extinguishing the FIRE: environmental quenching of satellite galaxies around Milky Way-mass hosts in simulations

   https://doi.org/10.1093/mnras/stac1706  

   Samuel, Jenna; Wetzel, Andrew; Santistevan, Isaiah; Tollerud, Erik; Moreno, Jorge; Boylan-Kolchin, Michael; Bailin, Jeremy; Pardasani, Bhavya (July 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The star formation and gas content of satellite galaxies around the Milky Way (MW) and Andromeda (M31) are depleted relative to more isolated galaxies in the Local Group (LG) at fixed stellar mass. We explore the environmental regulation of gas content and quenching of star formation in z = 0 galaxies at $$M_{*}=10^{5\!-\!10}\, \rm {M}_{\odot }$$ around 14 MW-mass hosts from the Feedback In Realistic Environments 2 (FIRE-2) simulations. Lower mass satellites ($$M_{*}\lesssim 10^7\, \rm {M}_{\odot }$$) are mostly quiescent and higher mass satellites ($$M_{*}\gtrsim 10^8\, \rm {M}_{\odot }$$) are mostly star forming, with intermediate-mass satellites ($$M_{*}\approx 10^{7\!-\!8}\, \rm {M}_{\odot }$$) split roughly equally between quiescent and star forming. Hosts with more gas in their circumgalactic medium have a higher quiescent fraction of massive satellites ($$M_{*}=10^{8\!-\!9}\, \rm {M}_{\odot }$$). We find no significant dependence on isolated versus paired (LG-like) host environments, and the quiescent fractions of satellites around MW-mass and Large Magellanic Cloud (LMC)-mass hosts from the FIRE-2 simulations are remarkably similar. Environmental effects that lead to quenching can also occur as pre-processing in low-mass groups prior to MW infall. Lower mass satellites typically quenched before MW infall as central galaxies or rapidly during infall into a low-mass group or a MW-mass galaxy. Most intermediate- to high-mass quiescent satellites have experienced ≥1–2 pericentre passages (≈2.5–5 Gyr) within a MW-mass halo. Most galaxies with $$M_{*}\gtrsim 10^{6.5}\, \rm {M}_{\odot }$$ did not quench before falling into a host, indicating a possible upper mass limit for isolated quenching. The simulations reproduce the average trend in the LG quiescent fraction across the full range of satellite stellar masses. Though the simulations are consistent with the Satellites Around Galactic Analogs (SAGA) survey’s quiescent fraction at $$M_{*}\gtrsim 10^8\, \rm {M}_{\odot }$$, they do not generally reproduce SAGA’s turnover at lower masses. 

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4. Identification and Quenching of Nugget Galaxies in the RESOLVE Survey at z = 0

   https://doi.org/10.3847/1538-4357/ad3ded  

   Carr, Derrick S; Kannappan, Sheila J; Norris, Mark A; Sinha, Manodeep; Palumbo, Michael L; Eckert, Kathleen D; Moffett, Amanda J; Polimera, Mugdha S; Bernstein, Joel I; Hutchens, Zackary L; et al (June 2024, The Astrophysical Journal)

   Abstract We present a complete census of candidate nuggets, i.e., dense galaxies likely formed by compaction with intense gas influx, within the volume-limited redshiftz∼ 0 REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. These nuggets span all evolutionary stages and 3 orders of magnitude in stellar mass (M_*∼ 10⁸to 10¹¹M_⊙) from the dwarf to the giant regime. We develop selection criteria for ourz∼ 0 nugget candidates based on structure and introduce the use of environmental criteria to eliminate nugget-like objects with suspected non-compaction origins. The resultingz∼ 0 nuggets follow expectations with respect to structure (i.e., density, size), population frequency, and likely origins. We show that the properties of our nugget census are consistent with permanent quenching above the gas-richness threshold scale (halo mass M_halo∼ 10^11.4M_⊙), cyclic temporary quenching below the threshold scale, and feedback from active galactic nuclei (AGN) assisting in permanent quenching. As predicted in simulations, most nuggets quench within a halo mass range ofM_halo∼ 10^11.45to 10^11.9M_⊙. We find ∼0.29 dex scatter around the star-forming main sequence for candidate blue nuggets below the threshold scale, which is consistent with temporary quenching as seen in simulations. A transitional population of green nuggets appears above the threshold scale. AGN also become more common in nuggets above this scale, and we see a likely AGN excess in nuggets versus comparably selected non-nuggets. Our results provide the first observational confirmation of the mass-dependent, AGN-mediated shift from cyclic quenching to halo quenching in nuggets. 

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5. Survivors and Zombies: The Quenching and Disruption of Satellites Around Milky Way Analogs

   https://doi.org/10.3847/1538-4357/adec94  

   Pathak, Debosmita; Christensen, Charlotte R; Brooks, Alyson M; Munshi, Ferah; Wright, Anna C; Carter, Courtney (August 2025, The Astrophysical Journal)

   Abstract It is necessary to understand the full accretion history of the Milky Way in order to contextualize the properties of observed Milky Way satellite galaxies and the stellar halo. This paper compares the dynamical properties and star formation histories of surviving and disrupted satellites around Milky Way–like galaxies using theD.C. Justice Leaguesuite of very high-resolution cosmological zoom-in simulations of Milky Way analogs and their halo environments. We analyze the full census of galaxies accreted within the past 12 Gyr, including both surviving satellites atz= 0, and dwarf galaxies that disrupted and merged with the host prior toz= 0. Our simulations successfully reproduce the trends inM_*−[Fe/H]−[α/Fe] observed in surviving Milky Way satellites and disrupted stellar streams, indicating earlier star formation for disrupted progenitors. We find the likelihood and timescales for quenching and disruption are strongly correlated with the mass and time of infall. In particular, none of the galaxies accreted more than 12 Gyr ago survived, and only 20% of all accreted galaxies withM_* > 10⁸M_⊙survive. Additionally, satellites with highly radial trajectories are more likely to quench and disrupt. Disruption proceeds quickly for ≥10⁶M_⊙satellites accreted 10–12 Gyr ago, often on timescales similar to the ∼300 Myr snapshot spacing. For high-mass satellites, the disruption timescale is faster than the quenching timescale. As a result, 92% of disrupted galaxies remain star forming up until disruption. In contrast, ultrafaint dwarfs (UFDs) tend to quench prior to accretion, and 94% of UFDs accreted up to 12 Gyr ago survive atz= 0. 

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