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1. 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)

   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$\log (M_{*}/M_{\odot })\ge 8$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,$8\le \log (M_{*}/M_{\odot })<9$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$\log (M_{*}/M_{\odot })<10$galaxies with decreasingd_nodeandd_fil,$\log (M_{*}/M_{\odot })\ge 10$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 densemore »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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2. Now You See It, Now You Don’t: Star Formation Truncation Precedes the Loss of Molecular Gas by ∼100 Myr in Massive Poststarburst Galaxies at z ∼ 0.6

   https://doi.org/10.3847/1538-4357/ac3dfa  

   Bezanson, Rachel ; Spilker, Justin S. ; Suess, Katherine A. ; Setton, David J. ; Feldmann, Robert ; Greene, Jenny E. ; Kriek, Mariska ; Narayanan, Desika ; Verrico, Margaret ( February 2022 , The Astrophysical Journal)

   We use ALMA observations of CO(2–1) in 13 massive (M_*≳ 10¹¹M_⊙) poststarburst galaxies atz∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu$$\overrightarrow{L}\mathrm{ar}$$momentum, and Evolution ($\mathit{SQuIGG}\vec{L}E$) program. Early results showed that two poststarburst galaxies host large H₂reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with$M_{{\mathrm{H}}_2}\gtrsim {10}^9$M_⊙. Given their high stellar masses, this mass limit corresponds to an average gas fraction of$〈f_{{\mathrm{H}}_2}\equiv M_{{\mathrm{H}}_2}/M_{*}〉\sim 7\%$or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with theD_n4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support thismore »empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H₂reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, the$\mathit{SQuIGG}\vec{L}E$galaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H₂scaling relations.

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3. Mapping Obscuration to Reionization with ALMA (MORA): 2 mm Efficiently Selects the Highest-redshift Obscured Galaxies

   https://doi.org/10.3847/1538-4357/ac2eb4  

   Casey, Caitlin M. ; Zavala, Jorge A. ; Manning, Sinclaire M. ; Aravena, Manuel ; Béthermin, Matthieu ; Caputi, Karina I. ; Champagne, Jaclyn B. ; Clements, David L. ; Drew, Patrick ; Finkelstein, Steven L. ; et al ( December 2021 , The Astrophysical Journal)

   We present the characteristics of 2 mm selected sources from the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey conducted to date, the Mapping Obscuration to Reionization with ALMA (MORA) survey covering 184 arcmin²at 2 mm. Twelve of 13 detections above 5σare attributed to emission from galaxies, 11 of which are dominated by cold dust emission. These sources have a median redshift of$〈z_{2\mathrm{mm}}〉={3.6}_{-0.3}^{+0.4}$primarily based on optical/near-infrared photometric redshifts with some spectroscopic redshifts, with 77% ± 11% of sources atz> 3 and 38% ± 12% of sources atz> 4. This implies that 2 mm selection is an efficient method for identifying the highest-redshift dusty star-forming galaxies (DSFGs). Lower-redshift DSFGs (z< 3) are far more numerous than those atz> 3 yet are likely to drop out at 2 mm. MORA shows that DSFGs with star formation rates in excess of 300M_⊙yr⁻¹and a relative rarity of ∼10⁻⁵Mpc⁻³contribute ∼30% to the integrated star formation rate density at 3 <z< 6. The volume density of 2 mm selected DSFGs is consistent with predictions from some cosmological simulations and is similar to the volume density of their hypothesized descendants: massive, quiescent galaxies atz> 2. Analysis of MORA sources’more »spectral energy distributions hint at steeper empirically measured dust emissivity indices than reported in typical literature studies, with$〈\beta 〉={2.2}_{-0.4}^{+0.5}$. The MORA survey represents an important step in taking census of obscured star formation in the universe’s first few billion years, but larger area 2 mm surveys are needed to more fully characterize this rare population and push to the detection of the universe’s first dusty galaxies.

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4. Short GRB Host Galaxies. II. A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for Their Neutron Star Merger Origins

   https://doi.org/10.3847/1538-4357/ac91d1  

   Nugent, Anya E. ; Fong, Wen-Fai ; Dong, Yuxin ; Leja, Joel ; Berger, Edo ; Zevin, Michael ; Chornock, Ryan ; Cobb, Bethany E. ; Kelley, Luke Zoltan ; Kilpatrick, Charles D. ; et al ( November 2022 , The Astrophysical Journal)

   We present the stellar population properties of 69 short gamma-ray burst (GRB) host galaxies, representing the largest uniformly modeled sample to date. Using theProspectorstellar population inference code, we jointly fit photometry and/or spectroscopy of each host galaxy. We find a population median redshift of$z={0.64}_{-0.32}^{+0.83}$(68% confidence), including nine photometric redshifts atz≳ 1. We further find a median mass-weighted age oft_m=${0.8}_{-0.53}^{+2.71}$Gyr, stellar mass of log(M_*/M_⊙) =${9.69}_{-0.65}^{+0.75}$, star formation rate of SFR =${1.44}_{-1.35}^{+9.37}$M_⊙yr⁻¹, stellar metallicity of log(Z_*/Z_⊙) =$-{0.38}_{-0.42}^{+0.44}$, and dust attenuation of$A_V={0.43}_{-0.36}^{+0.85}$mag (68% confidence). Overall, the majority of short GRB hosts are star-forming (≈84%), with small fractions that are either transitioning (≈6%) or quiescent (≈10%); however, we observe a much larger fraction (≈40%) of quiescent and transitioning hosts atz≲ 0.25, commensurate with galaxy evolution. We find that short GRB hosts populate the star-forming main sequence of normal field galaxies, but do not include as many high-mass galaxies as the general galaxy population, implying that their binary neutron star (BNS) merger progenitors are dependent on a combination of host star formation and stellar mass. The distribution of ages and redshifts implies a broad delay-time distribution,more »with a fast-merging channel atz> 1 and a decreased neutron star binary formation efficiency from high to low redshifts. If short GRB hosts are representative of BNS merger hosts within the horizon of current gravitational wave detectors, these results can inform future searches for electromagnetic counterparts. All of the data and modeling products are available on the Broadband Repository for Investigating Gamma-ray burst Host Traits website.

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5. Molecular Gas Reservoirs in Massive Quiescent Galaxies at z ∼ 0.7 Linked to Late-time Star Formation

   https://doi.org/10.3847/1538-4357/ac9af7  

   Woodrum, Charity ; Williams, Christina C. ; Rieke, Marcia ; Leja, Joel ; Johnson, Benjamin D. ; Bezanson, Rachel ; Kennicutt, Robert ; Spilker, Justin ; Tacchella, Sandro ( November 2022 , The Astrophysical Journal)

   We explore how the presence of detectable molecular gas depends on the inferred star formation histories (SFHs) in eight massive, quiescent galaxies atz∼ 0.7. Half of the sample have clear detections of molecular gas, traced by CO(2–1). We find that the molecular gas content is unrelated to the rate of star formation decline prior to the most recent 1 Gyr, suggesting that the gas reservoirs are not left over from their primary star formation epoch. However, the recent SFHs of CO-detected galaxies demonstrate evidence for secondary bursts of star formation in their last Gyr. The fraction of stellar mass formed in these secondary bursts ranges fromf_burst≈ 0.3%–6% and ended betweent_end-burst≈ 0–330 Myr ago. The CO-detected galaxies form a higher fraction of mass in the last Gyr ($f_{M_{1\mathrm{Gyr}}}=2.6\%\pm 1.8\%$) compared to the CO-undetected galaxies ($f_{M_{1\mathrm{Gyr}}}=0.2\%\pm 0.1\%$). The galaxies with gas reservoirs have enhanced late-time star formation, highlighting this as a contributing factor to the observed heterogeneity in the gas reservoirs in high-redshift quiescent galaxies. We find that the amount of gas and star formation driven by these secondary bursts are inconsistent with that expected from dry minor mergers, and instead are likely driven bymore »recently accreted gas, i.e., gas-rich minor mergers. This conclusion would not have been made based on SFR_UV+IRmeasurements alone, highlighting the power of detailed SFH modeling in the interpretation of gas reservoirs. Larger samples are needed to understand the frequency of low-level rejuvenation among quiescent galaxies at intermediate redshifts, and to what extent this drives the diversity of molecular gas reservoirs.

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