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1. ELVES. IV. The Satellite Stellar-to-halo Mass Relation Beyond the Milky Way

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

   Danieli, Shany; Greene, Jenny E; Carlsten, Scott; Jiang, Fangzhou; Beaton, Rachael; Goulding, Andy D (September 2023, The Astrophysical Journal)

   Abstract Quantifying the connection between galaxies and their host dark matter halos has been key for testing cosmological models on various scales. BelowM_⋆∼ 10⁹M_⊙, such studies have primarily relied on the satellite galaxy population orbiting the Milky Way (MW). Here we present new constraints on the connection between satellite galaxies and their host dark matter subhalos using the largest sample of satellite galaxies in the Local Volume (D≲ 12 Mpc) to date. We use 250 confirmed and 71 candidate dwarf satellites around 27 MW-like hosts from the Exploration of Local VolumE Satellites (ELVES) Survey and use the semianalyticalSatGenmodel for predicting the population of dark matter subhalos expected in the same volume. Through a Bayesian model comparison of the observed and the forward-modeled satellite stellar mass functions (SSMFs), we infer the satellite stellar-to-halo mass relation. We find that the observed SSMF is best reproduced when subhalos at the low-mass end are populated by a relation of the form $M_{\star }\propto M_{\mathrm{peak}}^{\alpha }$ , with a moderate slope of ${\alpha }_{\mathrm{const}}=2.10\pm 0.01$ and a low scatter, constant as a function of the peak halo mass, of ${\sigma }_{\mathrm{const}}={0.06}_{-0.05}^{+0.07}$ . A model with a steeper slope (α_grow= 2.39 ± 0.06) and a scatter that grows with decreasingM_peakis also consistent with the observed SSMF but is not required. Our new model for the satellite–subhalo connection, based on hundreds of Local Volume satellite galaxies, is in line with what was previously derived using only MW satellites. 

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2. 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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3. Ursa Major III/UNIONS 1: The Darkest Galaxy Ever Discovered?

   https://doi.org/10.3847/1538-4357/ad2267  

   Errani, Raphaël; Navarro, Julio F; Smith, Simon_E T; McConnachie, Alan W (April 2024, The Astrophysical Journal)

   Abstract The recently discovered stellar system Ursa Major III/UNIONS 1 (UMa3/U1) is the faintest known Milky Way satellite to date. With a stellar mass of ${16}_{-5}^{+6}{M}_{\odot }$ and a half-light radius of 3 ± 1 pc, it is either the darkest galaxy ever discovered or the faintest self-gravitating star cluster known to orbit the Galaxy. Its line-of-sight velocity dispersion suggests the presence of dark matter, although current measurements are inconclusive because of the unknown contribution to the dispersion of potential binary stars. We useN-body simulations to show that, if self-gravitating, the system could not survive in the Milky Way tidal field for much longer than a single orbit (roughly 0.4 Gyr), which strongly suggests that the system is stabilized by the presence of large amounts of dark matter. If UMa3/U1 formed at the center of a ∼10⁹M_⊙cuspy LCDM halo, its velocity dispersion would be predicted to be of order ∼1 km s⁻¹. This is roughly consistent with the current estimate, which, neglecting binaries, placesσ_losin the range 1–4 km s⁻¹. Because of its dense cusp, such a halo should be able to survive the Milky Way tidal field, keeping UMa3/U1 relatively unscathed until the present time. This implies that UMa3/U1 is plausibly the faintest and densest dwarf galaxy satellite of the Milky Way, with important implications for alternative dark matter models and for the minimum halo mass threshold for luminous galaxy formation in the LCDM cosmology. Our results call for multi-epoch high-resolution spectroscopic follow-up to confirm the dark matter content of this extraordinary system. 

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4. A little red dot at z = 7.3 within a large galaxy overdensity

   https://doi.org/10.1038/s41550-025-02660-1  

   Schindler, Jan-Torge; Hennawi, Joseph F; Davies, Frederick B; Bosman, Sarah_E I; Endsley, Ryan; Wang, Feige; Yang, Jinyi; Barth, Aaron J; Eilers, Anna-Christina; Fan, Xiaohui; et al (November 2025, Nature Astronomy)

   Abstract The nature of ‘little red dots’ and their relation to other forms of accreting supermassive black holes remain an open question. Here we report the discovery of a little red dot atz = 7.3. It is attenuated by moderate amounts of dust,A_V = 2.79 mag, and has an intrinsic bolometric luminosity of 10^46.6 erg s⁻¹and a supermassive black hole mass of 5 × 10⁸ M_⊙. Most notably, this object is embedded in an overdensity of eight nearby galaxies, allowing us to calculate a spectroscopic estimate of the clustering of galaxies around little red dots. We find a little red dot versus galaxy cross-correlation length ofr₀ = 8 ± 2 h⁻¹ cMpc, comparable to that ofz ≈ 6 ultraviolet-luminous quasars. The resulting estimate of their minimum dark matter halo mass$$\log_{10}({M}_{{\rm{halo}},\min }/{{{M}}}_{\odot })=12.{0}_{-1.0}^{+0.8}$$ ${\log }_{10}\left(M_{\mathrm{halo},\min }/M_{\odot }\right)=12.0_{-1.0}^{+0.8}$ indicates that nearly all haloes above this mass must host actively accreting supermassive black holes atz ≈ 7, in strong contrast with the far smaller duty cycle of luminous quasars (<1%). Our results, taken at face value, motivate a picture in which supermassive black holes in little red dot phases could serve as the obscured precursors of ultraviolet-luminous quasars, which provides a natural explanation for the short ultraviolet-luminous lifetimes inferred from both quasar clustering and quasar proximity zones. 

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5. A JWST View of the Overmassive Black Hole in NGC 4486B

   https://doi.org/10.3847/2041-8213/adf728  

   Tahmasebzadeh, Behzad; Taylor, Matthew A; Valluri, Monica; Yoshino, Haruka; Vasiliev, Eugene; Drinkwater, Michael J; Thompson, Solveig; Dage, Kristen; Côté, Patrick; Ferrarese, Laura; et al (August 2025, The Astrophysical Journal Letters)

   Abstract We present a new stellar dynamical measurement of the supermassive black hole in the compact elliptical galaxy NGC 4486B, based on integral field spectroscopy with JWST/NIRSpec. The two-dimensional kinematic maps reveal a resolved double nucleus and a velocity dispersion peak offset from the photometric center. Utilizing two independent methods—Schwarzschild orbit-superposition and Jeans anisotropic modeling—we tightly constrain the black hole mass by fitting the full line-of-sight velocity distribution. Our axisymmetric Schwarzschild models yield a best-fit black hole mass of ${\mathcal{M}}_{\mathrm{BH}}$ $=3.6_{-0.7}^{+0.7}\times 10^{8}M\odot$ , slightly lower but significantly more precise than previous estimates. However, since our models do not account for the nonequilibrium nature of the double nucleus, this value may represent a lower limit. Across all tested dynamical models, the inferred ${\mathcal{M}}_{\mathrm{BH}}$ /M_*ratio ranges from ∼4% to 13%, providing robust evidence for an overmassive SMBH in NGC 4486B. Combined with the galaxy’s location deep within the Virgo Cluster, our results support the interpretation that NGC 4486B is the tidally stripped remnant core of a formerly massive galaxy. As the JWST/NIRSpec field of view is insufficient to constrain the dark matter halo, we incorporate archival ground-based long-slit kinematics extending to 5″. While this provides some leverage on the dark matter content, the constraints remain relatively weak. We place only an upper limit on the dark matter fraction, with ${\mathcal{M}}_{\mathrm{DM}}$ / ${\mathcal{M}}_{*}$ ≲0.5 within 1 kpc—well beyond the effective radius. The inferred black hole mass remains unchanged with or without a dark matter halo. 

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