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1. The Circumgalactic Medium of Extreme Emission Line Galaxies at z∼2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyα Emission in the KBSS-KCWI Survey*

   https://doi.org/10.3847/1538-4357/acd849  

   Erb, Dawn K.; Li 李智, Zhihui 慧.; Steidel, Charles C.; Chen 陈昱, Yuguang 光.; Gronke, Max; Strom, Allison L.; Trainor, Ryan F.; Rudie, Gwen C. (August 2023, The Astrophysical Journal)

   Abstract The resonantly scattered Lyαline illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyαemission in 12 relatively low-mass (M_⋆∼ 10⁹M_⊙)z∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyαblue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyαand absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the Hicolumn density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the Hicolumn density in the outer halos. 

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2. Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows

   https://doi.org/10.3847/1538-4357/acc660  

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

   Abstract We present results on the properties of extreme gas outflows in massive (M_*∼ 10¹¹M_⊙), compact, starburst (star formation rate, SFR∼ 200M_⊙yr⁻¹) galaxies atz= 0.4–0.7 with very high star formation surface densities (Σ_SFR∼ 2000M_⊙yr⁻¹kpc⁻²). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies, we identify outflows with maximum velocities of 820–2860 km s⁻¹. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T∼ 10⁴K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies’ star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong Mgiiabsorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of ∼50–2200M_⊙yr⁻¹, assuming a fiducial outflow size of 5 kpc, and mass loading factors ofη∼ 5 for most of the sample. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution. 

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3. A complete census of circumgalactic Mg  ii at redshift z ≲ 0.5

   https://doi.org/10.1093/mnras/stab360  

   Huang, Yun-Hsin; Chen, Hsiao-Wen; Shectman, Stephen A; Johnson, Sean D; Zahedy, Fakhri S; Helsby, Jennifer E; Gauthier, Jean-René; Thompson, Ian B (February 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT This paper presents a survey of Mg ii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mg ii absorption and H α emission. The projected distances span a range from d = 9 to 497 kpc, redshifts of the galaxies range from z = 0.10 to 0.48, and rest-frame absolute B-band magnitudes range from MB = −16.7 to −22.8. Our analysis shows that the rest-frame equivalent width of Mg ii, Wr(2796), depends on halo radius (Rh), B-band luminosity(LB), and stellar mass (Mstar) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, Wr(2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mg ii absorbing gas 〈κ〉 is high with 〈κ〉 ≳ 60 per cent at <40 kpc for isolated galaxies and declines rapidly to 〈κ〉 ≈ 0 at d ≳ 100 kpc. Within the gaseous radius, the incidence of Mg ii gas depends sensitively on both Mstar and the specific star formation rate inferred from H α. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mg ii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to $$m_{\rm cl} \gtrsim 10^5 \, \rm M_\odot$$ and cool gas accretion rate of $$\sim 0.7\!-\!2 \, \mathrm{ M}_\odot \, \rm yr^{-1}$$. Finally, we find no strong azimuthal dependence of Mg ii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space. 

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4. Extending the Dynamic Range of Galaxy Outflow Scaling Relations: Massive Compact Galaxies with Extreme Outflows

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

   Davis, Julie D.; Tremonti, Christy A.; Swiggum, Cameren N.; Moustakas, John; Diamond-Stanic, Aleksandar M.; Coil, Alison L.; Geach, James E.; Hickox, Ryan C.; Perrotta, Serena; Petter, Grayson C.; et al (July 2023, The Astrophysical Journal)

   Abstract We investigate galactic winds in the HizEA galaxies, a collection of 46 late-stage galaxy mergers atz= 0.4–0.8, with stellar masses of $\log \left(M_{*}/M_{\odot }\right)=10.4–11.5$, star formation rates (SFRs) of 20–500M_⊙yr⁻¹, and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mgiiλλ2796,2803 absorption lines in optical spectra from MMT, Magellan, and Keck. We find evidence of outflows in 90% of targets, with maximum outflow velocities of 550–3200 km s⁻¹. We combine these data with ten samples from the literature to construct scaling relations for outflow velocity versus SFR, star formation surface density (Σ_SFR),M_*, and SFR/M_*. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of ∼2–4 in outflow velocity and an order of magnitude in SFR and Σ_SFR. The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R, and Σ_SFR, and weaker correlations withM_*and SFR/M_*. The HizEA galaxies are mild outliers on the SFR andM_*scaling relations, but they connect smoothly with more typical star-forming galaxies on plots of outflow velocity versus SFR/Rand Σ_SFR. These results provide further evidence that the HizEA galaxies’ exceptional outflow velocities are a consequence of their extreme star formation conditions rather than hidden black hole activity, and they strengthen previous claims that Σ_SFRis one of the most important properties governing the velocities of galactic winds. 

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5. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Impact of Galaxies on the Circumgalactic Medium Metal Enrichment at z > 6 Using the JWST and VLT

   https://doi.org/10.3847/2041-8213/ad23e7  

   Zou, Siwei; Cai, Zheng; Wang, Feige; Fan, Xiaohui; Champagne, Jaclyn B; Hennawi, Joseph F; Schindler, Jan-Torge; Farina, Emanuele Paolo; Yang, Jinyi; Inayoshi, Kohei; et al (February 2024, The Astrophysical Journal Letters)

   Abstract We characterize the multiphase circumgalactic medium (CGM) and galaxy properties atz= 6.0–6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305–3150 to identify one new metal absorber atz= 6.2713 with multiple transitions (Oi, Mgii, Feii,and Cii). They are combined with the published absorbing systems in Davies et al. at the same redshift range to form a sample of nine metal absorbers atz= 6.03–6.49. We identify eight galaxies within 1000 km s⁻¹and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [Oiii] (λλ4959, 5007) doublets and Hβemission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar masses ranging from 10^7.2to 10^8.8M_⊙and metallicity between 0.02 and 0.4 solar. Notably, thez= 6.2713 system in the J0305–3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances ofαelements to iron ([α/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [α/Fe] ratio. Our modeling of the galaxy’s chemical abundance favors a top-heavy stellar initial mass function and hints that we may be witnessing the contribution of the first generation of Population III stars to the CGM at the end of the reionization epoch. 

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