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1. A Possible “Too-many-satellites” Problem in the Isolated Dwarf Galaxy DDO 161

   https://doi.org/10.3847/2041-8213/ae3ddd  

   Li_李, Jiaxuan 嘉轩; Greene, Jenny E; Danieli, Shany; Carlsten, Scott G; Geha, Marla (February 2026, The Astrophysical Journal Letters)

   Abstract The abundance of satellite galaxies provides a direct test of ΛCDM and galaxy formation physics on small scales. While satellites of Milky Way-mass galaxies are well studied, those of dwarf galaxies remain largely unexplored. We present a systematic search for satellites around the isolated dwarf galaxy DDO 161 (M_⋆ ≈ 10^8.4M_⊙) at a distance of 6 Mpc. We identify eight satellite candidates within the projected virial radius and confirm three new satellites through surface brightness fluctuation distance measurements from deep Magellan imaging data. Together with its confirmed satellite UGCA 319, DDO 161 has four confirmed satellites above $M_{\star }^{\mathrm{sat}}>10^{5.4}{M}_{\odot }$ , making it the most satellite-rich dwarf galaxy known to date. We compare this system with predictions from the TNG50 cosmological simulation, combined with currently established galaxy–halo connection models calibrated on Milky Way satellites, and find that DDO 161 has a satellite abundance far exceeding all current expectations. The rich satellite system of DDO 161 offers new insight into how low-mass galaxies occupy dark matter halos in low-density environments and may provide new constraints on the nature of dark matter. 

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2. ASPIRE: The Environments and Dark Matter Halos of Luminous Quasars in the Epoch of Reionization

   https://doi.org/10.3847/1538-4357/ae7bfa  

   Wang, Feige; Champagne, Jaclyn B; Huang, Jiamu; Yang, Jinyi; Hennawi, Joseph F; Fan, Xiaohui; Zhang, Haowen; Costa, Tiago; Decarli, Roberto; Habouzit, Melanie; et al (July 2026, The Astrophysical Journal)

   Abstract We present a systematic study of the environments of 25 luminous quasars atz > 6.5 from the ASPIRE program. Using JWST/NIRCam wide-field slitless spectroscopy data, we identified 487 galaxies at 5.3 ≲ z ≲ 7.0 exhibiting [Oiii] emission. Among these, 122 [Oiii] emitters lie within ∣Δv_los∣ < 1000 km s⁻¹of the quasars, corresponding to a ∼9.4-fold enhancement relative to the average galaxy density at other redshifts. Furthermore, we identified 16 [Cii]-emitting galaxies at the quasar redshifts from Atacama Large Millimeter/submillimeter Array (ALMA) mosaic observations. A cross-correlation function analysis between quasars and [Oiii]+[Cii] emitters yields a cross-correlation length of $r_0^{\mathrm{QG}}=8.68_{-0.55}^{+0.51}{h}^{-1}\mathrm{cMpc}$ and an autocorrelation of $r_0^{\mathrm{QQ}}=15.76_{-2.70}^{+2.48}{h}^{-1}\mathrm{cMpc}$ , indicating thatz ∼ 7 quasars reside in dark matter halos with $M_{\mathrm{halo}}=10^{12.27_{-0.26}^{+0.21}}{M}_{\odot }$ and have a quasar lifetime of $t_Q=10^{{7.05}_{-1.01}^{+0.95}}\mathrm{yr}$ . Notably, the number of [Oiii]-emitting galaxies at quasar redshifts varies significantly from field to field, ranging from 0 to 20, highlighting a diverse quasar environment. Remarkably, seven quasars trace significant galaxy overdensities (i.e., protoclusters), withδ_gal > 5 within a volume ofV ∼ 500 cMpc³. We also find that ∣Δv_los∣ increases rapidly toward smaller galaxy–quasar separations in protocluster fields, consistent with galaxy kinematics around extremely massive halos in cosmological simulations. By combining JWST and ALMA data, we reveal the complex and diverse environments of these early quasars, providing robust evidence that the earliest luminous quasars are effective tracers of galaxy overdensities, albeit with substantial field-to-field variation. 

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3. A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55

   https://doi.org/10.3847/1538-4357/ad07d0  

   McNanna, M; Bechtol, K; Mau, S; Nadler, E O; Medoff, J; Drlica-Wagner, A; Cerny, W; Crnojević, D; Mutlu-Pakdıl, B; Vivas, A K; et al (January 2024, The Astrophysical Journal)

   Abstract We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete toM_V∼ (−7, −10) mag for galaxies atD= (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of ${2.2}_{-0.12}^{+0.05}\mathrm{Mpc}$ , a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absoluteV-band magnitude of $-{8.0}_{-0.3}^{+0.5}\mathrm{mag}$ and an azimuthally averaged physical half-light radius of ${2.2}_{-0.4}^{+0.5}\mathrm{kpc}$ , making this one of the lowest surface brightness galaxies ever found with $\mu =32.3\mathrm{mag}{\mathrm{arcsec}}^{-2}$ . This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host. 

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4. Chemodynamics of Boötes I with S ⁵ : Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints

   https://doi.org/10.3847/1538-4357/ae2fe5  

   Sandford, Nathan R; Li, Ting S; Koposov, Sergey E; Hayashi, Kohei; Pace, Andrew B; Erkal, Denis; Bovy, Jo; Da_Costa, Gary S; Cullinane, Lara R; Ji, Alexander P; et al (February 2026, The Astrophysical Journal)

   Abstract We combine new spectroscopic observations of the ultrafaint dwarf (UFD) galaxy Boötes I (Boo I) from the Southern Stellar Stream Spectroscopic Survey (S⁵) with ∼15 yr of archival spectroscopic data to create the largest sample of stellar kinematics and metallicities to date for any Milky Way UFD. Our combined sample includes 148 members extending out to ∼7 half-light radii (r_h), including 24 newly confirmed members, 18 binary candidates, 15 RR Lyrae stars, and 92 [Fe/H] measurements. Using this larger and more spatially extended sample, we provide updated constraints on Boo I’s systemic properties, including its radial population gradients. Properly accounting for perspective rotation effects in a UFD for the first time, we detect a 4σline-of-sight velocity gradient of 1.2 ± 0.3 km s⁻¹ $r_h^{-1}$ aligned along Boo I’s orbit and discuss its potential tidal origins. We also infer a metallicity gradient of −0.10 ± 0.02 dex $r_h^{-1}$ in agreement with previous studies. Using an axisymmetric Jeans model, we provide updated constraints on Boo I’s dark matter density profile, which weakly favors a cusped ( $\gamma =1.0_{-0.6}^{+0.5}$ ) dark matter profile. Lastly, we reanalyze Boo I’s metallicity distribution function with a one-zone galactic chemical evolution model and place new constraints on its rapid, inefficient star formation and strong galactic outflows. 

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5. Stellar Metallicities and Gradients in the Faint M31 Satellites Andromeda XVI and Andromeda XXVIII

   https://doi.org/10.3847/1538-4357/ad76a2  

   Fu, Sal Wanying; Weisz, Daniel R; Starkenburg, Else; Martin, Nicolas; Collins, Michelle_L M; Savino, Alessandro; Boylan-Kolchin, Michael; Côté, Patrick; Dolphin, Andrew E; Longeard, Nicolas; et al (October 2024, The Astrophysical Journal)

   Abstract We present ∼300 stellar metallicity measurements in two faint M31 dwarf galaxies, Andromeda XVI (M_V= −7.5) and Andromeda XXVIII (M_V= –8.8), derived using metallicity-sensitive calcium H and K narrowband Hubble Space Telescope imaging. These are the first individual stellar metallicities in And XVI (95 stars). Our And XXVIII sample (191 stars) is a factor of ∼15 increase over literature metallicities. For And XVI, we measure $〈\mathrm{[Fe/H]}〉=-{2.17}_{-0.05}^{+0.05}$ , ${\sigma }_{\mathrm{[Fe/H]}}={0.33}_{-0.07}^{+0.07}$ , and ∇_[Fe/H]= −0.23 ± 0.15 dex $R_e^{-1}$ . We find that And XVI is more metal-rich than Milky Way ultrafaint dwarf galaxies of similar luminosity, which may be a result of its unusually extended star formation history. For And XXVIII, we measure $〈\mathrm{[Fe/H]}〉=-{1.95}_{-0.04}^{+0.04}$ , ${\sigma }_{\mathrm{[Fe/H]}}={0.34}_{-0.05}^{+0.05}$ , and ∇_[Fe/H]= −0.46 ± 0.10 dex $R_e^{-1}$ , placing it on the dwarf galaxy mass–metallicity relation. Neither galaxy has a metallicity distribution function (MDF) with an abrupt metal-rich truncation, suggesting that star formation fell off gradually. The stellar metallicity gradient measurements are among the first for faint (L≲ 10⁶L_⊙) galaxies outside the Milky Way halo. Both galaxies’ gradients are consistent with predictions from the FIRE simulations, where an age–gradient strength relationship is the observational consequence of stellar feedback that produces dark matter cores. We include a catalog for community spectroscopic follow-up, including 19 extremely metal-poor ([Fe/H] < –3.0) star candidates, which make up 7% of And XVI’s MDF and 6% of And XXVIII’s. 

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