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1. Spatially Resolved Circumgalactic Medium around a Star-forming Galaxy Driving a Galactic Outflow at z  ≈ 0.8

   https://doi.org/10.3847/1538-4357/add0b9  

   Shaban, Ahmed; Bordoloi, Rongmon; O’Meara, John M; Sharon, Keren; Tejos, Nicolas; Lopez, Sebastian; Ledoux, Cédric; Barrientos, L Felipe; Rigby, Jane R (June 2025, The Astrophysical Journal)

   Abstract We report the small-scale spatial variation in cool (T ∼ 10⁴K) Mgiiabsorption detected in the circumgalactic medium (CGM) of a star-forming galaxy atz ≈ 0.8. The CGM of this galaxy is probed by a spatially extended bright background gravitationally lensed arc atz= 2.76. The background arc continuously samples the CGM of the foreground galaxy at a range of impact parameters between 54 and 66 kpc. The Mgiiabsorption strengths vary by more than a factor of 2 within these ranges. A power-law fit to the fractional variation of absorption strengths yields a coherence length of 5.8 kpc within this range of impact parameters. This suggests a high degree of spatial coherence in the CGM of this galaxy. The host galaxy is driving a strong galactic outflow with a mean outflow velocity ≈ −179 km s⁻¹and mass outflow rate ${\dot{M}}_{\mathrm{out}}\ge 64_{-27}^{+31}$M_⊙yr⁻¹traced by blueshifted Mgiiand Feiiabsorption lines. The galaxy itself has a spatially extended emission halo with a maximum spatial extent of ≈33 kpc traced by [Oii], [Oiii], and Hβemission lines. The extended emission halo shows kinematic signatures of corotating halo gas with solar metallicity. Taken together, these observations suggest evidence of a baryon cycle that is recycling the outflowing gas to form the next generation of stars. 

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2. The Cosmic Ultraviolet Baryon Survey (CUBS). VII. On the Warm-hot Circumgalactic Medium Probed by O vi and Ne viii at 0.4 ≲ z ≲ 0.7

   https://doi.org/10.3847/1538-4357/ad410b  

   Qu, Zhijie; Chen, Hsiao-Wen; Johnson, Sean D; Rudie, Gwen C; Zahedy, Fakhri S; DePalma, David; Schaye, Joop; Boettcher, Erin T; Cantalupo, Sebastiano; Chen, Mandy C; et al (June 2024, The Astrophysical Journal)

   Abstract This paper presents a newly established sample of 103 unique galaxies or galaxy groups at 0.4 ≲z≲ 0.7 from the Cosmic Ultraviolet Baryon Survey (CUBS) for studying the warm-hot circumgalactic medium (CGM) probed by both Oviand Neviiiabsorption. The galaxies and associated neighbors are identified at <1 physical Mpc from the sightlines toward 15 CUBS QSOs atz_QSO≳ 0.8. A total of 30 galaxies or galaxy groups exhibit associated Oviλλ1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km s⁻¹, while the rest show no trace of Ovito a detection limit of $\log N_{\mathrm{OVI}}/{\mathrm{cm}}^{-2}\approx 13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Neviiiλλ770, 780 doublet absorption, down to a limiting column density of $\log N_{\mathrm{NeVIII}}/{\mathrm{cm}}^{-2}\approx 14.0$. These Ovi- and Neviii-bearing halos reside in different galaxy environments with stellar masses ranging from $\log M_{\mathrm{star}}/M_{\odot }\approx 8$to ≈11.5. The warm-hot CGM around galaxies of different stellar masses and star formation rates exhibits different spatial profiles and kinematics. In particular, star-forming galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9–11$show a significant concentration of metal-enriched warm-hot CGM within the virial radius, while massive quiescent galaxies exhibit flatter radial profiles of both column densities and covering fractions. In addition, the velocity dispersion of Oviabsorption is broad withσ_υ> 40 km s⁻¹for galaxies of $\log M_{\mathrm{star}}/M_{\odot }>9$within the virial radius, suggesting a more dynamic warm-hot halo around these galaxies. Finally, the warm-hot CGM probed by Oviand Neviiiis suggested to be the dominant phase in sub-L* galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9–10$based on their high ionization fractions in the CGM. 

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3. CloudFlex: A Flexible Parametric Model for the Small-scale Structure of the Circumgalactic Medium

   https://doi.org/10.3847/1538-4357/ad5965  

   Hummels, Cameron_B; Rubin, Kate_H_R; Schneider, Evan_E; Fielding, Drummond_B (September 2024, The Astrophysical Journal)

   Abstract We presentCloudFlex, an open-source tool for predicting absorption-line signatures of cool gas in galaxy halos with small-scale structure. Motivated by analyses of ∼10⁴K material in hydrodynamical simulations of turbulent, multiphase media, we model cool gas structures as complexes of cloudlets sampled from a power-law distribution of mass $\propto m_{\mathrm{cl}}^{-\alpha }$with velocities drawn from a turbulent velocity field. The user may specifyα, the lower limit of the cloudlet mass distribution ( $m_{\mathrm{cl},\min }$), and several other parameters that set the mass, size, and velocity distribution of the complex. This permits investigation of the relation between these parameters and absorption-line observables. As a proof-of-concept, we calculate the Mgiiλ2796 absorption induced by the cloudlets in background quasi-stellar object (QSO) spectra. We demonstrate that, at fixed metallicity, the covering fraction of sight lines with equivalent widthsW₂₇₉₆< 0.3 Å increases significantly with decreasing $m_{\mathrm{cl},\min }$, cloudlet number density (n_cl), and complex size. We then use this framework to predict the halo-scaleW₂₇₉₆distribution around ∼L^*galaxies. We show that the observed incidences ofW₂₇₉₆> 0.3 Å sight lines with impact parameters 10 kpc <R_⊥< 50 kpc in projected QSO–galaxy studies are consistent with our model over much of parameter space. However, they are underpredicted by models with $m_{\mathrm{cl},\min }\ge 100M_{\odot }$andn_cl≥ 0.03 cm⁻³, in keeping with a picture in which the inner cool circumgalactic medium (CGM) is dominated by numerous low-mass cloudlets (m_cl≲ 100M_⊙) with a volume filling factor ≲1%. When used to model absorption-line data sets built from multi-sight line and/or spatially extended background probes,CloudFlexenables detailed constraints on the size and velocity distributions of structures comprising the photoionized CGM. 

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4. Resolved Velocity Profiles of Galactic Winds at Cosmic Noon

   https://doi.org/10.3847/1538-4357/acf462  

   Vasan G. C., Keerthi; Jones, Tucker; Sanders, Ryan L.; Ellis, Richard S.; Stark, Daniel P.; Kacprzak, Glenn G.; Barone, Tania M.; Tran, Kim-Vy H.; Glazebrook, Karl; Jacobs, Colin (December 2023, The Astrophysical Journal)

   Abstract We study the kinematics of the interstellar medium (ISM) viewed “down the barrel” in 20 gravitationally lensed galaxies during cosmic noon (z= 1.5–3.5). We use moderate-resolution spectra (R∼ 4000) from Keck’s Echellette Spectrograph and Imager and Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into ∼10 independent elements and use double Gaussian fits to quantify the velocity structure of the gas. We find that the bulk motion of gas in this galaxy sample is outflowing, with average velocity centroid $\left(v_{\mathrm{cent}}\right)=-141$km s⁻¹(±111 km s⁻¹scatter) measured with respect to the systemic redshift. A total of 16 out of the 20 galaxies exhibit a clear positive skewness, with a blueshifted tail extending to ∼ −500 km s⁻¹. We examine scaling relations in outflow velocities with galaxy stellar mass and star formation rate, finding correlations consistent with a momentum-driven wind scenario. Our measured outflow velocities are also comparable to those reported for FIRE-2 and TNG50 cosmological simulations at similar redshift and galaxy properties. We also consider implications for interpreting results from lower-resolution spectra. We demonstrate that while velocity centroids are accurately recovered, the skewness, velocity width, and probes of high-velocity gas (e.g.,v₉₅) are subject to large scatter and biases at lower resolution. We find thatR≳ 1700 is required for accurate results for the gas kinematics of our sample. This work represents the largest available sample of well-resolved outflow velocity structure atz> 2 and highlights the need for good spectral resolution to recover accurate properties. 

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5. The Ionization and Dynamics of the Makani Galactic Wind

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

   Rupke, David S.; Coil, Alison L.; Perrotta, Serena; Davis, Julie D.; Diamond-Stanic, Aleksandar M.; Geach, James E.; Hickox, Ryan C.; Moustakas, John; Petter, Grayson C.; Rudnick, Gregory H.; et al (April 2023, The Astrophysical Journal)

   Abstract The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I;R_I= 20 − 50 kpc) and the fast, inner wind is 7 Myr old (Episode II;R_II= 0 − 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase—the warm, ionized gas—are unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out tor= 30–40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200–400 km s⁻¹shocks that power the ionized gas, withv_shock=σ_wind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas: $M_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim M_{\mathrm{II}}^{{\mathrm{H}}_2}=(1-2)\times {10}^9{M}_{\odot }$and $\mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim \mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{{\mathrm{H}}_2}=170-250M_{\odot }$yr⁻¹. The outer wind has slowed, so that $\mathit{dM}/{\mathit{dt}}_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}\sim 10M_{\odot }$yr⁻¹, but it contains more ionized gas, $M_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}=5\times {10}^9$M_⊙. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p“boost” ∼7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium. 

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