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1. 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)

   Abstract 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 $\log \left(M_{\mathrm{BH}}/M_{\odot }\right)={7.01}_{-0.33}^{+0.23}+{1.74}_{-0.64}^{+0.64}\log \left(M_{*,\mathrm{host}}/{10}^{10}{M}_{\odot }\right)$, 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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2. 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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3. The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

   https://doi.org/10.3847/1538-4357/acf46f  

   Savino, Alessandro; Weisz, Daniel R.; Skillman, Evan D.; Dolphin, Andrew; Cole, Andrew A.; Kallivayalil, Nitya; Wetzel, Andrew; Anderson, Jay; Besla, Gurtina; Boylan-Kolchin, Michael; et al (October 2023, The Astrophysical Journal)

   Abstract We present the lifetime star formation histories (SFHs) for six ultrafaint dwarf (UFD;M_V> − 7.0, $4.9<{\log }_{10}\left(M_{*}\right(z=0\left)/M_{\odot }\right)<5.5$) satellite galaxies of M31 based on deep color–magnitude diagrams constructed from Hubble Space Telescope imaging. These are the first SFHs obtained from the oldest main-sequence turnoff of UFDs outside the halo of the Milky Way (MW). We find that five UFDs formed at least 50% of their stellar mass byz= 5 (12.6 Gyr ago), similar to known UFDs around the MW, but that 10%–40% of their stellar mass formed at later times. We uncover one remarkable UFD, Andxiii, which formed only 10% of its stellar mass byz= 5, and 75% in a rapid burst atz∼ 2–3, a result that is robust to choices of underlying stellar model and is consistent with its predominantly red horizontal branch. This “young” UFD is the first of its kind and indicates that not all UFDs are necessarily quenched by reionization, which is consistent with predictions from several cosmological simulations of faint dwarf galaxies. SFHs of the combined MW and M31 samples suggest reionization did not homogeneously quench UFDs. We find that the least-massive MW UFDs (M_*(z= 5) ≲ 5 × 10⁴M_⊙) are likely quenched by reionization, whereas more-massive M31 UFDs (M_*(z= 5) ≳ 10⁵M_⊙) may only have their star formation suppressed by reionization and quench at a later time. We discuss these findings in the context of the evolution and quenching of UFDs. 

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4. Properties of Nuclear Star Clusters in Low Surface Brightness Galaxies

   https://doi.org/10.3847/1538-3881/ad4ed3  

   Khim, Donghyeon J; Zaritsky, Dennis; Lambert, Mika; Donnerstein, Richard (July 2024, The Astronomical Journal)

   Abstract Using the Systematically Measuring Ultra-Diffuse Galaxies and Sloan Digital Sky Survey catalogs and our own reprocessing of the Legacy Survey imaging, we investigate the properties of nuclear star clusters (NSCs) in galaxies having central surface brightnesses as low as 27 mag arcsec⁻². We identify 273 (123 with known redshift) and 32 NSC-bearing galaxies in the two samples, respectively, where we require candidate NSCs to have a separation of less than 0.10r_efrom the galaxy center. We find that galaxies with low central surface brightness (μ_0,g> 24 mag arcsec⁻²) are more likely to contain an NSC if they (1) have a higher stellar mass, (2) have a higher stellar-to-total mass ratio, (3) have a brighter central surface brightness, (4) have a larger axis ratio, or (5) lie in a denser environment. Because of the correlations among these various quantities, it is likely that only one or two are true physical drivers. We also find scaling relations for the NSC mass with stellar mass (M_NSC/ $M_{\odot }={10}^{6.02\pm 0.03}{(M_{*,\mathrm{gal}}/{10}^8{M}_{\odot })}^{0.77\pm 0.04}$) and halo mass (M_NSC/ $M_{\odot }={10}^{6.11\pm 0.05}{(M_{h,\mathrm{gal}}/{10}^{10}{M}_{\odot })}^{0.92\pm 0.05}$), although it is the scaling with halo mass that is consistent with a direct proportionality. In galaxies with an NSC,M_NSC≈ 10⁻⁴M_h,gal. This proportionality echoes the finding of a direct proportionality between the mass (or number) of globular clusters (GCs) in galaxies and the galaxy’s total mass. These findings favor a related origin for GCs and NSCs. 

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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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