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1. Observational Signatures of AGN Feedback in the Morphology and the Ionization States of Milky Way-like Galaxies

   https://doi.org/10.3847/1538-4357/ad8658  

   Qutob, Nadia; Emami, Razieh; Su, Kung-Yi; Smith, Randall; Hernquist, Lars; Triani, Dian P; Hummels, Cameron; Fielding, Drummond; Hopkins, Philip F; Somerville, Rachel S; et al (December 2024, The Astrophysical Journal)

   Abstract We make an in-depth analysis of different active galactic nuclei (AGN) jet models’ signatures, inducing quiescence in galaxies with a halo mass of 10¹²M_⊙. Three jet models, including cosmic-ray-dominant, hot thermal, and precessing kinetic jets, are studied at two energy flux levels each, compared to a jet-free, stellar feedback-only simulation. Each of our simulations is idealized isolated galaxy simulations with AGN jet powers that are constant in time and generated using GIZMO and with FIRE stellar feedback. We examine the distribution of Mgii, Ovi, and Oviiiions, alongside gas temperature and density profiles. Low-energy ions, like Mgii, concentrate in the interstellar medium (ISM), while higher energy ions, e.g., Oviii, prevail at the AGN jet cocoon’s edge. High-energy flux jets display an isotropic ion distribution with lower overall density. High-energy thermal or cosmic-ray jets pressurize at smaller radii, significantly suppressing core density. The cosmic-ray jet provides extra pressure support, extending cool and warm gas distribution. A break in the ion-to-mass ratio slope in Oviand Oviiiis demonstrated in the ISM-to-circumgalactic medium (CGM) transition (between 10 and 30 kpc), growing smoothly toward the CGM at greater distances. 

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2. Highly Ionized Gas in the Zone of Avoidance: Using the CIViL ^⋆ Survey to Pinpoint Physical Conditions of Gaseous Halos

   https://doi.org/10.3847/1538-4357/ae0304  

   Garza, Samantha L; Faerman, Yakov; Berg, Trystyn_A M; Werk, Jessica K; Oppenheimer, Benjamin D; Bordoloi, Rongmon; Ellison, Sara (October 2025, The Astrophysical Journal)

   Abstract This paper investigates the physical conditions of the circumgalactic medium ofL^⋆galaxies through explorations of observed ion tracer gas kinematics and comparisons of observations to different ionization models. For this analysis, we utilize Civobservations from the CIViL^⋆survey (∼0.14 ≤z_gal≤ 0.25) and directly compare them to observations of matched lines of sight from the Cosmic Origins Spectrograph-Halos survey. We find that the kinematic parameters for Civand Oviare likely (>95%) drawn from the same parent distribution, suggesting that these two ions are kinematically coincident andpotentiallyoriginate under the same physical conditions. We find that the measured Civ/Oviand Nv/Oviratios are inconsistent with single-phase equilibrium models. For 70% of the objects in our sample, regions allowed by the column density ratios in the density-temperature space do not overlap, creating a “zone of avoidance.” We also investigate the origins of Civ, Nv, and Oviby exploring a cooling flow model under collisional ionization. We find that both Nvand Oviare consistent with the predictions of the model, but the column densities of Civare ∼2.5 times higher than the predictions. As Civhas a lower ionization energy than Nvand Ovi, it is possible that Civhas contributions from both the warm/hot and cool photoionized phase. 

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3. Properties of the circumgalactic medium in cosmic ray-dominated galaxy haloes

   https://doi.org/10.1093/mnras/staa1849  

   Ji, Suoqing; Chan, T K; Hummels, Cameron B; Hopkins, Philip F; Stern, Jonathan; Kereš, Dušan; Quataert, Eliot; Faucher-Giguère, Claude-André; Murray, Norman (August 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass haloes hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity $$\kappa \sim 3\times 10^{29}\, \mathrm{cm^2\ s^{-1}}$$ chosen to match γ-ray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MW-mass haloes at z ≲ 1–2. The gas in these ‘CR-dominated’ haloes differs significantly from runs without CRs: the gas is primarily cool (a few $${\sim}10^{4}\,$$ K), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. Ionization of the ‘low’ and ‘mid’ ions in this diffuse cool gas is dominated by photoionization, with O vi columns $${\gtrsim}10^{14.5}\, \mathrm{cm^{-2}}$$ at distances $${\gtrsim}150\, \mathrm{kpc}$$. CR and thermal gas pressure are locally anticorrelated, maintaining total pressure balance, and the CGM gas density profile is determined by the balance of CR pressure gradients and gravity. Neglecting CRs, the same haloes are primarily warm/hot ($$T\gtrsim 10^{5}\,$$K) with thermal pressure balancing gravity, collisional ionization dominates, O vi columns are lower and Ne viii higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase. 

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4. MUSEQuBES: Physical Conditions, Origins, and Multielement Abundances of the Circumgalactic Medium of an Isolated, Star-forming Dwarf Galaxy at z = 0.57

   https://doi.org/10.3847/2041-8213/ae2f5f  

   Johnson, Sean D; Mishra, Nishant; Muzahid, Sowgat; Rudie, Gwen C; Zahedy, Fakhri S; Qu, Zhijie; Faucher-Giguère, Claude-André; Stern, Jonathan; Li, Jennifer I-Hsiu; Fuller, Elise; et al (January 2026, The Astrophysical Journal Letters)

   Abstract In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf atz= 0.5723 with a stellar mass of ≈5 × 10⁷M_⊙and star formation rate (≈0.05M_⊙yr⁻¹) and ISM metallicity ([O/H] ≈ −0.9) consistent with the star-forming main sequence and mass–metallicity relation. A background quasar sight line with archival UV spectra probes the dwarf’s CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf’s CGM is detected in Hi;intermediate metal ions of Ciii, Oiii, Oiv, and Sv; and kinematically broader, highly ionized Ovibut is undetected in Nivand Neviii. Photoionization modeling of the intermediate ions indicates a modest volume filling factor (∼6% along the sight line or ∼2% globally) and a mass of ∼2 × 10⁸M_⊙, ∼4× higher than the dwarf’s stellar mass but ∼10× less than the highly ionized CGM. The Ovikinematics are comparable to the dwarf’s estimated virial velocity, suggesting that it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is [O/H] = −0.6, but with low relative abundances of [C/O] = −0.6 and [N/O] < −1.0. The [N/O] is below levels expected of the dwarf’s ISM but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars. 

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5. Mainly on the Plane: Observing the Extended, Ionized Disks of Milky Way Analogs in IllustrisTNG

   https://doi.org/10.3847/1538-4357/ae48e8  

   Messere, Michael; Tchernyshyov, Kirill; Putman, Mary E; Bryan, Greg L; Werk, Jessica K; Zheng, Yong; Schiminovich, David (March 2026, The Astrophysical Journal)

   Abstract This paper explores the extent to which the circumgalactic medium (CGM) of Milky Way (MW)-like galaxies is located in an extended, ionized, disklike structure. To test this hypothesis, we analyze the spatial and kinematic distributions of different ion species within a sample of MW-like systems in IllustrisTNG. We model commonly observed ions (HI, MgII, SiIV, CIV, and OVI) and calculate (1) their angular momentum misalignment from the star-forming disk (θ) and (2) the fraction of absorption consistent with galaxy rotation (f_EWcorot). We find that 63% of Mgii, 45% of Siiv, 38% of Civ, and 35% of Ovimass along the major axis have kinematics aligned with the galaxy angular momentum axis. We extend this to a mock absorption line survey and quantifyf_EWcorot. We find thatf_EWcorot(Mgii) ∼ 80% andf_EWcorot(Ovi) ∼ 60% at ∼0.5R_200c, in agreement with recent observational work. We find that in the typical MW analog, there is evidence of cool–warm material in an extended, corotating structure, regardless of whether the angular momentum or observational definition is used. Hence, we expect that the typical MW CGM, especially in the low ions, should be mainly on the plane. 

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