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1. The MASSIVE Survey. XVI. The Stellar Initial Mass Function in the Center of MASSIVE Early-type Galaxies

   https://doi.org/10.3847/1538-4357/ac69ea  

   Gu, Meng ; Greene, Jenny E. ; Newman, Andrew B. ; Kreisch, Christina ; Quenneville, Matthew E. ; Ma, Chung-Pei ; Blakeslee, John P. ( June 2022 , The Astrophysical Journal)

   The stellar initial mass function (IMF) is a fundamental property in the measurement of stellar masses and galaxy star formation histories. In this work, we focus on the most massive galaxies in the nearby universe$\log (M_{\star }/M_{\odot })>11.2$. We obtain high-quality Magellan/LDSS-3 long-slit spectroscopy with a wide wavelength coverage of 0.4–1.01μm for 41 early-type galaxies (ETGs) in the MASSIVE survey and derive high signal-to-noise spectra within an aperture ofR_e/8. Using detailed stellar synthesis models, we constrain the elemental abundances and stellar IMF of each galaxy through full spectral modeling. All the ETGs in our sample have an IMF that is steeper than a Milky Way (Kroupa) IMF. The best-fit IMF mismatch parameter,α_IMF= (M/L)/(M/L)_MW, ranges from 1.1 to 3.1, with an average of 〈α_IMF〉 = 1.84, suggesting that on average, the IMF is more bottom heavy than Salpeter. Comparing the estimated stellar masses with the dynamical masses, we find that most galaxies have stellar masses that are smaller than their dynamical masses within the 1σuncertainty. We complement our sample with lower-mass galaxies from the literature and confirm that$\log ({\alpha }_{\mathrm{IMF}})$is positively correlated with$\log (\sigma )$,$\log (M_{\star })$, and$\log (M_{\mathrm{dyn}})$. From the combined sample, we show that the IMF in the centers of more massive ETGs is more bottom heavy. In addition, we find that$\log ({\alpha }_{\mathrm{IMF}})$is positively correlated with both [Mg/Fe] and the estimated total metallicity [Z/H]. We find suggestive evidence that the effective stellar surface density Σ_Kroupamight be responsible for the variation ofα_IMF. We conclude thatσ, [Mg/Fe], and [Z/H] are the primary drivers of the global stellar IMF variation.

    

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2. The Direct-method Oxygen Abundance of Typical Dwarf Galaxies at Cosmic High Noon∗

   https://doi.org/10.3847/1538-4357/acb153  

   Gburek, Timothy ; Siana, Brian ; Alavi, Anahita ; Emami, Najmeh ; Richard, Johan ; Freeman, William R. ; Stark, Daniel P. ; Snapp-Kolas, Christopher ( May 2023 , The Astrophysical Journal)

   We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲z≲ 2.6 (z_mean= 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of$\log {(M_{*}/M_{\odot })}_{\mathrm{med}}={8.29}_{-0.43}^{+0.51}$and a median star formation rate of${\mathrm{S}\mathrm{F}\mathrm{R}}_{\mathrm{H}\alpha }^{\mathrm{m}\mathrm{e}\mathrm{d}}={2.25}_{-1.26}^{+2.15}{M}_{\odot }{\mathrm{y}\mathrm{r}}^{-1}$. We measure the faint electron-temperature-sensitive [Oiii]λ4363 emission line at 2.5σ(4.1σ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of$12+\log {(\mathrm{O}/\mathrm{H})}_{\mathrm{direct}}={7.88}_{-0.22}^{+0.25}$(${0.15}_{-0.06}^{+0.12}{Z}_{\odot }$). We investigate the applicability at highzof locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixedM_*, our composite is well represented by thez∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories$(\log {(M_{*}/M_{\odot })}_{\mathrm{med}}={8.92}_{-0.22}^{+0.31})$, we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixedM_*and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii]λ3729/[Oii]λ3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of$n_e=1_{-0}^{+215}{\mathrm{cm}}^{-3}$($n_e=1_{-0}^{+74}{\mathrm{cm}}^{-3}$) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies atz∼ 2.

    

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3. The Sloan Digital Sky Survey Reverberation Mapping Project: The Black Hole Mass–Stellar Mass Relations at 0.2 ≲ z ≲ 0.8

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

   Li, Jennifer I-Hsiu ; Shen, Yue ; Ho, Luis C. ; Brandt, W. N. ; Grier, Catherine J. ; Hall, Patrick B. ; Homayouni, Y. ; Koekemoer, Anton M. ; Schneider, Donald P. ; Trump, Jonathan R. ( September 2023 , The Astrophysical Journal)

   We measure the correlation between black hole massM_BHand host stellar massM_*for a sample of 38 broad-line quasars at 0.2 ≲z≲ 0.8 (median redshiftz_med= 0.5). The black hole masses are derived from a dedicated reverberation mapping program for distant quasars, and the stellar masses are derived from two-band optical+IR Hubble Space Telescope imaging. Most of these quasars are well centered within ≲1 kpc from the host galaxy centroid, with only a few cases in merging/disturbed systems showing larger spatial offsets. Our sample spans two orders of magnitude in stellar mass (∼10⁹–10¹¹M_⊙) and black hole mass (∼10⁷–10⁹M_⊙) and reveals a significant correlation between the two quantities. We find a best-fit intrinsic (i.e., selection effects corrected)M_BH–M_*,hostrelation of$\log (M_{\mathrm{BH}}/M_{\odot })={7.01}_{-0.33}^{+0.23}+{1.74}_{-0.64}^{+0.64}\log (M_{*,\mathrm{host}}/{10}^{10}{M}_{\odot })$, with an intrinsic scatter of${0.47}_{-0.17}^{+0.24}$dex. Decomposing our quasar hosts into bulges and disks, there is a similarM_BH–M_*,bulgerelation with slightly larger scatter, likely caused by systematic uncertainties in the bulge–disk decomposition. TheM_BH–M_*,hostrelation atz_med= 0.5 is similar to that in local quiescent galaxies, with negligible evolution over the redshift range probed by our sample. With direct black hole masses from reverberation mapping and the large dynamical range of the sample, selection biases do not appear to affect our conclusions significantly. Our results, along with other samples in the literature, suggest that the locally measured black hole mass–host stellar mass relation is already in place atz∼ 1.

    

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4. High-redshift Galaxy Candidates at z = 9–10 as Revealed by JWST Observations of WHL0137-08

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

   Bradley, Larry D. ; Coe, Dan ; Brammer, Gabriel ; Furtak, Lukas J. ; Larson, Rebecca L. ; Kokorev, Vasily ; Andrade-Santos, Felipe ; Bhatawdekar, Rachana ; Bradač, Maruša ; Broadhurst, Tom ; et al ( September 2023 , The Astrophysical Journal)

   We report the discovery of four galaxy candidates observed 450–600 Myr after the Big Bang with photometric redshifts betweenz∼ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) NIRCam imaging of the galaxy cluster WHL0137−08 observed in eight filters spanning 0.8–5.0μm, plus nine Hubble Space Telescope filters spanning 0.4–1.7μm. One candidate is gravitationally lensed with a magnification ofμ∼ 8, while the other three are located in a nearby NIRCam module with expected magnifications ofμ≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range$\log M_{\star }/M_{\odot }$= 8.3–8.7. All appear young, with mass-weighted ages <240 Myr, low dust contentA_V< 0.15 mag, and specific star formation rates sSFR ∼0.25–10 Gyr⁻¹for most. Onez∼ 9 candidate is consistent with an age <5 Myr and an sSFR ∼10 Gyr⁻¹, as inferred from a strong F444W excess, implying [Oiii]+Hβrest-frame equivalent width ∼2000 Å, although an olderz∼ 10 object is also allowed. Anotherz∼ 9 candidate is lensed into an arc 2.″4 long with a magnification ofμ∼ 8. This arc is the most spatially resolved galaxy atz∼ 9 known to date, revealing structures ∼30 pc across. Follow-up spectroscopy of WHL0137−08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.

    

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5. 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)

   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 ($\log (M_{\star }/M_{\odot })$> 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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