Detection of hot, metal-enriched outflowing gas around $z\approx$2.3 star-forming galaxies in the Keck Baryonic Structure Survey

Abstract

We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift $z\approx 2.3$ star-forming galaxies taken from the Keck Baryonic Structure Survey (KBSS). In Turner et al. 2014 we used the pixel optical depth technique to show that absorption by HI and the metal ions OVI, NV, CIV, CIII and SiIV is strongly enhanced within $|\Delta v|\lesssim 170$ km/s and projected distances $|d|\lesssim 180$ proper kpc from sightlines to the background quasars. Here we demonstrate that the OVI absorption is also strongly enhanced at fixed HI, CIV, and SiIV optical depths, and that this enhancement extends out to $\sim 350$ km/s. At fixed HI the increase in the median OVI optical depth near galaxies is 0.3-0.7 dex and is detected at 2--3-$\sigma$ confidence for all seven HI bins that have ${\log }_{10}{\tau }_{\mathrm{HI}}\ge -1.5$. We use ionization models to show that the observed strength of OVI as a function of HI is consistent with enriched, photoionized gas for pixels with ${\tau }_{\mathrm{HI}}\gtrsim 10$. However, for pixels with ${\tau }_{\mathrm{HI}}\lesssim 1$ this would lead to implausibly high metallicities at low densities if the gas were photoionized by the background radiation. This indicates that the galaxies are surrounded by gas that is sufficiently hot to be collisionally ionized ($T>10^5$K) and that a substantial fraction of the hot gas has a metallicity $\gtrsim 10^{-1}$ of solar. Given the high metallicity and large velocity extent (out to $\sim 1.5\times v_{\mathrm{circ}}$) of this gas, we conclude that we have detected hot, metal enriched outflows arising from star-forming galaxies.

Accepted for publication in MNRAS, 14 pages, 9 figures (not including appendices)

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• The Circumgalactic Medium
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• The Keck Baryonic Structure Survey: Using foreground/background galaxy pairs to trace the structure and kinematics of circumgalactic neutral hydrogen at $z\sim 2$
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• Empirically Constrained Predictions for Metal-Line Emission from the Circumgalactic Medium
• Time-Dependent Cooling in Photoionized Plasma
• The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z=2.071
• The Impact of Cosmic Rays on the Kinematics of the Circumgalactic Medium
• Cold and Hot gas distribution around the Milky-Way-M31 system in the HESTIA simulations
• The relationship between gas and galaxies at z<1 using the Q0107 quasar triplet
• Properties of the circumgalactic medium in simulations compared to observations
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• Identifying Circumgalactic Medium Absorption in QSO Spectra: A Bayesian Approach
• Origin of Weak MgII and Higher Ionization Absorption Lines in an Outflow from an Intermediate-Redshift Dwarf Satellite Galaxy
• Metal-strong Inflows at the Outer-galactic-scale of a Quasar