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1. DESI Massive Poststarburst Galaxies at z ∼ 1.2 Have Compact Structures and Dense Cores

   https://doi.org/10.3847/1538-4357/ad7c45  

   Zhang, Yunchong; Setton, David_J; Price, Sedona_H; Bezanson, Rachel; Khullar, Gourav; Newman, Jeffrey_A; Aguilar, Jessica_Nicole; Ahlen, Steven; Andrews, Brett_H; Brooks, David; et al (November 2024, The Astrophysical Journal)

   Abstract Poststarburst galaxies (PSBs) are young quiescent galaxies that have recently experienced a rapid decrease in star formation, allowing us to probe the fast-quenching period of galaxy evolution. In this work, we obtained Hubble Space Telescope (HST)/WFC3 F110W imaging to measure the sizes of 171 massive ( $\log (M_{*}/M_{\odot })\sim 11)$spectroscopically identified PSBs at 1 <z1.3 selected from the DESI Survey Validation luminous red galaxy sample. This statistical sample constitutes an order of magnitude increase from the ∼20 PSBs with space-based imaging and deep spectroscopy. We perform structural fitting of the target galaxies withpysersicand compare them to quiescent and star-forming galaxies in the 3D-HST survey. We find that these PSBs are more compact than the general population of quiescent galaxies, lying systematically ∼0.1 dex below the established size–mass relation. However, their central surface mass densities are similar to those of their quiescent counterparts ( $\log \left({\mathrm{\Sigma }}_{1\mathrm{kpc}}/\right(M_{\odot }{\mathrm{kpc}}^{-2}\left)\right)\sim 10.1$). These findings are easily reconciled by later ex situ growth via minor mergers or a slight progenitor bias. These PSBs are round in projection (b/a_median∼ 0.8), suggesting that they are primarily spheroids, not disks, in 3D. We find no correlation between the time since quenching and light-weighted PSB sizes or central densities. This disfavors apparent structural growth due to the fading of centralized starbursts in this galaxy population. Instead, we posit that the fast quenching of massive galaxies at this epoch occurs preferentially in galaxies with preexisting compact structures. 

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2. The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at z ∼ 3–5

   https://doi.org/10.3847/1538-4357/ad8b30  

   Antwi-Danso, Jacqueline; Papovich, Casey; Esdaile, James; Nanayakkara, Themiya; Glazebrook, Karl; Hutchison, Taylor_A; Whitaker, Katherine_E; Marsan, Z_Cemile; Diaz, Ruben_J; Marchesini, Danilo; et al (December 2024, The Astrophysical Journal)

   Abstract The measured ages of massive, quiescent galaxies atz∼ 3–4 imply that massive galaxies quench as early asz∼ 6. While the number of spectroscopic confirmations of quiescent galaxies atz< 3 has increased over the years, there are only a handful atz> 3.5. We report spectroscopic redshifts of one secure (z= 3.757) and two tentative (z= 3.336 andz= 4.673) massive ( $\log \left(M_{*}/M_{\odot }\right)>10.3$) quiescent galaxies with 11 hr of Keck/MOSFIREK-band observations. Our candidates were selected from the FLAMINGOS-2 Extragalactic Near-InfraredK-band Split (FENIKS) survey, which uses deep Gemini/Flamingos-2K_bK_rimaging optimized for increased sensitivity to the characteristic red colors of galaxies atz> 3 with a strong Balmer/4000 Å break. The rest-frameUVJand (ugi)_scolors of three out of four quiescent candidates are consistent with 1–2 Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies atz> 3 are all recently quenched, post-starburst galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line active galactic nucleus (z= 3.594) with strong, redshifted Hβ+ [OIII] emission with a velocity offset > 1000 km s⁻¹, indicative of a powerful outflow. The star formation history of our highest redshift candidate suggests that its progenitor was already in place byz∼ 7–11, reaching ∼10¹¹M_⊙byz≃ 8. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies atz> 4 is feasible only with JWST. 

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3. A Comparison of Star-formation Histories Derived from UniverseMachine and LEGA-C at 0.6 < z < 1

   https://doi.org/10.3847/2515-5172/ad1be9  

   Steel, Cecilia; Pearl, Alan; Kaushal, Yasha; Bezanson, Rachel (January 2024, Research Notes of the AAS)

   Abstract In this work, we compare star formation histories of massive (10.5 $<\log \left(M_{*}/M_{\odot }\right)<$12) galaxies in the UniverseMachine model to those measured from the Large Early Galaxy Astrophysics Census (LEGA-C) at 0.6 < z < 1. Following the LEGA-C study, we investigate how 50% (t₅₀) and 90% (t₉₀) formation timescales depend on total stellar mass. We find good agreement between the observed and model timescales for the star-forming population Δ t_SF ≲ 1 Gyr across the full mass range. In contrast, the observed age-mass correlation is weaker for the quiescent population compared to UniverseMachine models (Δt_Q ≲ 2 Gyr), especially at the high-mass end. This indicates continued star formation or additional processes in the most massive quiescent galaxies, a behavior not accounted for in the UniverseMachine model. 

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4. The Evolving Effect of Cosmic Web Environment on Galaxy Quenching

   https://doi.org/10.3847/1538-4357/acd11c  

   Hasan, Farhanul; Burchett, Joseph N.; Abeyta, Alyssa; Hellinger, Douglas; Mandelker, Nir; Primack, Joel R.; Faber, S. M.; Koo, David C.; Elek, Oskar; Nagai, Daisuke (June 2023, The Astrophysical Journal)

   Abstract We investigate how cosmic web structures affect galaxy quenching in the IllustrisTNG (TNG100) cosmological simulations by reconstructing the cosmic web within each snapshot using the DisPerSE framework. We measure the comoving distance from each galaxy with stellar mass $\log \left(M_{*}/M_{\odot }\right)\ge 8$to the nearest node (d_node) and the nearest filament spine (d_fil) to study the dependence of both the median specific star formation rate (〈sSFR〉) and the median gas fraction (〈f_gas〉) on these distances. We find that the 〈sSFR〉 of galaxies is only dependent on the cosmic web environment atz< 2, with the dependence increasing with time. Atz≤ 0.5, $8\le \log \left(M_{*}/M_{\odot }\right)<9$galaxies are quenched atd_node≲ 1 Mpc, and have significantly suppressed star formation atd_fil≲ 1 Mpc, trends driven mostly by satellite galaxies. Atz≤ 1, in contrast to the monotonic drop in 〈sSFR〉 of $\log \left(M_{*}/M_{\odot }\right)<10$galaxies with decreasingd_nodeandd_fil, $\log \left(M_{*}/M_{\odot }\right)\ge 10$galaxies—both centrals and satellites—experience an upturn in 〈sSFR〉 atd_node≲ 0.2 Mpc. Much of this cosmic web dependence of star formation activity can be explained by an evolution in 〈f_gas〉. Our results suggest that in the past ∼10 Gyr, low-mass satellites are quenched by rapid gas stripping in dense environments near nodes and gradual gas starvation in intermediate-density environments near filaments. At earlier times, cosmic web structures efficiently channeled cold gas into most galaxies. State-of-the-art ongoing spectroscopic surveys such as the Sloan Digital Sky Survey and DESI, as well as those planned with the Subaru Prime Focus Spectrograph, JWST, and Roman, are required to test our predictions against observations. 

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5. Active Galactic Nucleus Quenching in Simulated Dwarf Galaxies

   https://doi.org/10.3847/1538-4357/ace046  

   Sharma, Ray S; Brooks, Alyson M; Tremmel, Michael; Bellovary, Jillian; Quinn, Thomas R (October 2023, The Astrophysical Journal)

   Abstract We examine the quenching characteristics of 328 isolated dwarf galaxies $\left({10}^8<M_{\mathrm{star}}/M_{\odot }<{10}^{10}\right)$within theRomulus25cosmological hydrodynamic simulation. Using mock-observation methods, we identify isolated dwarf galaxies with quenched star formation and make direct comparisons to the quenched fraction in the NASA Sloan Atlas (NSA). Similar to other cosmological simulations, we find a population of quenched, isolated dwarf galaxies belowM_star< 10⁹M_⊙not detected within the NSA. We find that the presence of massive black holes (MBHs) inRomulus25is largely responsible for the quenched, isolated dwarfs, while isolated dwarfs without an MBH are consistent with quiescent fractions observed in the field. Quenching occurs betweenz= 0.5–1, during which the available supply of star-forming gas is heated or evacuated by MBH feedback. Mergers or interactions seem to play little to no role in triggering the MBH feedback. At low stellar masses,M_star≲ 10^9.3M_⊙, quenching proceeds across several Gyr as the MBH slowly heats up gas in the central regions. At higher stellar masses,M_star≳ 10^9.3M_⊙, quenching occurs rapidly within 1 Gyr, with the MBH evacuating gas from the central few kpc of the galaxy and driving it to the outskirts of the halo. Our results indicate the possibility of substantial star formation suppression via MBH feedback within dwarf galaxies in the field. On the other hand, the apparent overquenching of dwarf galaxies due to MBH suggests that higher-resolution and/or better modeling is required for MBHs in dwarfs, and quenched fractions offer the opportunity to constrain current models. 

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