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1. 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 董, Yuxin 雨欣; Leja, Joel; Berger, Edo; Zevin, Michael; Chornock, Ryan; Cobb, Bethany E.; Kelley, Luke Zoltan; Kilpatrick, Charles D.; et al (November 2022, The Astrophysical Journal)

   Abstract 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, 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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2. Cosmography with the Double-source-plane Strong Gravitational Lens AGEL 150745+052256

   https://doi.org/10.3847/1538-4357/adf442  

   Sahu, Nandini; Shajib, Anowar J; Tran, Kim-Vy; Skobe, Hannah; Rhoades, Sunny; Jones, Tucker; Glazebrook, Karl; Collett, Thomas E; Suyu, Sherry H; Vasan_G_C, Keerthi; et al (September 2025, The Astrophysical Journal)

   Strong gravitational lenses with two background sources at widely separated redshifts are a promising independent probe of cosmological parameters. We can use these systems, known as double-source-plane lenses (DSPLs), to measure the ratio (β) of angular-diameter distances of the sources, which is sensitive to the matter density (Ω_m) and the equation-of-state parameter for dark-energy (w). However, DSPLs are rare and require high-resolution imaging and spectroscopy for detection, lens modeling, and measuringβ. Here, we report only the second DSPL ever used to measure cosmological parameters. We model the DSPLAGEL150745+052256 from the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey using Hubble Space Telescope/Wide-Field Camera 3 imaging and Keck Cosmic Web Imager spectroscopy. The spectroscopic redshifts for the deflector and two sources inAGEL1507 arez_defl= 0.594,z_S1 =  2.163, andz_S2= 2.591. We measure a stellar velocity dispersion ofσ_obs = 109 ± 27 km s⁻¹for the nearer source (S1). Usingσ_obsfor the main deflector (from literature) and S1, we test the robustness of our DSPL model. We measure $\beta =0.953_{-0.010}^{+0.008}$forAGEL1507 and infer Ω_m $=0.33_{-0.23}^{+0.38}$for ΛCDM cosmology. CombiningAGEL1507 with the published model of the Jackpot lens improves the precision on Ω_m(ΛCDM) andw(wCDM) by ∼10%. The inclusion of DSPLs significantly improves the constraints when combined with Planck’s cosmic microwave background observations, enhancing the precision onwby 30%. This paper demonstrates the potential constraining power of DSPLs and their complementarity to other standard cosmological probes. Tighter future constraints from larger DSPL samples discovered from ongoing and forthcoming large-area sky surveys would provide insights into the nature of dark energy. 

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3. DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at z ∼ 1

   https://doi.org/10.3847/2041-8213/acc9b5  

   Setton, David J.; Dey, Biprateep; Khullar, Gourav; Bezanson, Rachel; Newman, Jeffrey A.; Aguilar, Jessica N.; Ahlen, Steven; Andrews, Brett H.; Brooks, David; de la Macorra, Axel; et al (April 2023, The Astrophysical Journal Letters)

   Abstract We utilize ∼17,000 bright luminous red galaxies (LRGs) from the novel Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample, leveraging its deep (∼2.5 hr galaxy⁻¹exposure time) spectra to characterize the contribution of recently quenched galaxies to the massive galaxy population at 0.4 <z< 1.3. We useProspectorto infer nonparametric star formation histories and identify a significant population of recently quenched galaxies that have joined the quiescent population within the past ∼1 Gyr. The highest-redshift subset (277 atz> 1) of our sample of recently quenched galaxies represents the largest spectroscopic sample of post-starburst galaxies at that epoch. At 0.4 <z< 0.8, we measure the number density of quiescent LRGs, finding that recently quenched galaxies constitute a growing fraction of the massive galaxy population with increasing look-back time. Finally, we quantify the importance of this population among massive ( $\log \left(M_{\star }/M_{\odot }\right)$> 11.2) LRGs by measuring the fraction of stellar mass each galaxy formed in the gigayear before observation,f_{1 Gyr}. Although galaxies withf_{1 Gyr}> 0.1 are rare atz∼ 0.4 (≲0.5% of the population), byz∼ 0.8, they constitute ∼3% of massive galaxies. Relaxing this threshold, we find that galaxies withf_{1 Gyr}> 5% constitute ∼10% of the massive galaxy population atz∼ 0.8. We also identify a small but significant sample of galaxies atz= 1.1–1.3 that formed withf_{1 Gyr}> 50%, implying that they may be analogs to high-redshift quiescent galaxies that formed on similar timescales. Future analysis of this unprecedented sample promises to illuminate the physical mechanisms that drive the quenching of massive galaxies after cosmic noon. 

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4. Discovery of Super-enriched Gas ∼1 Gyr after the Big Bang

   https://doi.org/10.3847/2041-8213/aceefe  

   Huyan 呼延, Jianghao 江豪; Kulkarni, Varsha P.; Poudel, Suraj; Tejos, Nicolas; Péroux, Celine; Lopez, Sebastian (August 2023, The Astrophysical Journal Letters)

   Abstract Abundances of chemical elements in the interstellar and circumgalactic media of high-redshift galaxies offer important constraints on the nucleosynthesis by early generations of stars. Damped Lyαabsorbers (DLAs) in spectra of high-redshift background quasars are excellent sites for obtaining robust measurements of element abundances in distant galaxies. Past studies of DLAs at redshiftsz> 4 have measured abundances of ≲0.01 solar. Here we report the discovery of a DLA atz= 4.7372 with an exceptionally high degree of chemical enrichment. We estimate the Hicolumn density in this absorber to be log (N_{H I}/cm⁻²) = 20.48 ± 0.15. Our analysis shows unusually high abundances of carbon and oxygen ([C/H] = 0.88 ± 0.17, [O/H] = 0.71 ± 0.16). Such a high level of enrichment a mere 1.2 Gyr after the Big Bang is surprising because of insufficient time for the required amount of star formation. To our knowledge, this is the first supersolar absorber found atz> 4.5. We find the abundances of Si and Mg to be [Si/H] = $-{0.56}_{-0.35}^{+0.40}$and [Mg/H] = ${0.59}_{-0.50}^{+0.27}$, confirming the metal-rich nature of this absorber. By contrast, Fe shows a much lower abundance ([Fe/H] = $-{1.53}_{-0.15}^{+0.15}$). We discuss implications of our results for galactic chemical evolution models. The metallicity of this absorber is higher than that of any other known DLA and is >2 orders of magnitude above predictions of chemical evolution models and theN_{H I}-weighted mean metallicity from previous studies atz> 4.5. The relative abundances (e.g., [O/Fe] = 2.29 ± 0.05, [C/Fe] = 2.46 ± 0.08) are also highly unusual compared to predictions for enrichment by early stars. 

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5. Spectroscopic Confirmation of a Protocluster at z = 3.37 with a High Fraction of Quiescent Galaxies

   https://doi.org/10.3847/1538-4357/ac2b9f  

   McConachie, Ian; Wilson, Gillian; Forrest, Ben; Marsan, Z. Cemile; Muzzin, Adam; Cooper, M. C.; Annunziatella, Marianna; Marchesini, Danilo; Chan, Jeffrey C. C.; Gomez, Percy; et al (February 2022, The Astrophysical Journal)

   Abstract We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically confirmed protocluster at $z={3.3665}_{-0.0012}^{+0.0009}$around a spectroscopically confirmedUVJ-quiescent ultramassive galaxy (UMG; $M_{\star }={2.34}_{-0.34}^{+0.23}\times {10}^{11}{M}_{\odot }$) in the COSMOS UltraVISTA field. We present a total of 38 protocluster members (14 spectroscopic and 24 photometric), including the UMG. Notably, and in marked contrast to protoclusters previously reported at this epoch that have been found to contain predominantly star-forming members, we measure an elevated fraction of quiescent galaxies relative to the coeval field ( ${73.3}_{-16.9}^{+26.7}\mathrm{\%}$versus ${11.6}_{-4.9}^{+7.1}\mathrm{\%}$for galaxies with stellar massM_⋆≥ 10¹¹M_⊙). This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of star-forming galaxies in protoclusters atz> 2 and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early universe. We discuss the possibility that we might be observing either “early mass quenching” or nonclassical “environmental quenching.” We also present the discovery of MAGAZ3NE J100028+023349, a second spectroscopically confirmed protocluster, at a very similar redshift of $z={3.3801}_{-0.0281}^{+0.0213}$. We present a total of 20 protocluster members, 12 of which are photometric and eight spectroscopic including a poststarburst UMG ( $M_{\star }={2.95}_{-0.20}^{+0.21}\times {10}^{11}{M}_{\odot }$). Protoclusters MAGAZ3NE J0959 and MAGAZ3NE J1000 are separated by 18′ on the sky (35 comoving Mpc), in good agreement with predictions from simulations for the size of “Coma”-type cluster progenitors at this epoch. It is highly likely that the two UMGs are the progenitors of Brightest Cluster Galaxies seen in massive virialized clusters at lower redshift. 

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