The formation and physical origin of highly ionized cooling gas

Abstract

We present a simple model that explains the origin of warm diffuse gas seen primarily as highly ionized absorption line systems in the spectra of background sources. We predict the observed column densities of several highly ionized transitions such as OVI, OVIII, NeVIII, NV, and MgX; and present a unified comparison of the model predictions with absorption lines seen in the Milky Way disk, Milky Way halo,starburst galaxies, the circumgalactic medium and the intergalactic medium at low and high redshifts. We show that diffuse gas seen in such diverse environments can be simultaneously explained by a simple model of radiatively cooling gas. We show that most of such absorption line systems are consistent with being collisionally ionized, and estimate the maximum likelihood temperature of the gas in each observation. This model satisfactorily explains why OVI is regularly observed around star-forming low-z L* galaxies, and why NV is rarely seen around the same galaxies. We further present some consequences of this model in quantifying the dynamics of the cooling gas around galaxies and predict the shock velocities associated with such flows. A unique strength of this model is that while it has only one free (but physically well-constrained) parameter, it nevertheless successfully reproduces the available data on O VI absorbers in the interstellar, circumgalactic, intra-group, and intergalactic media, as well as the available data on other absorption-line from highly ionized species.

15 pages, 10 figures, Accepted in ApJ, Substantial Revision, Simulation section added, new NeVIII vs OVI comparison added

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• Comparison of Theoretical Starburst Photoionisation Models for Optical Diagnostics
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• Exploring the Physical Properties of the Cool Circumgalactic Medium with a Semi-Analytic Model
• The CGM${}^2$ Survey: Quenching and the Transformation of the Circumgalactic Medium
• The diversity of the circumgalactic medium around z = 0 Milky Way-mass galaxies from the Auriga simulations
• Hunting for Metals Using XQ-100 Legacy Survey Composite Spectra
• The Mass and Absorption Columns of Galactic Gaseous Halos II -- The High Ionization State Ions
• Spatially Resolved Gas Flows Around the Milky Way
• Physical Conditions of Five O VI Absorption Systems Towards PG $1522+101$
• Detection of a Multiphase Intragroup Medium: Results from the COS-IGrM Survey
• Detection of Low Metallicity Warm Plasma in a Galaxy Overdensity Environment at z ~ 0.2
• A High Signal-to-Noise HST Spectrum Toward J1009+0713: Precise Absorption Measurements in the CGM of Two Galaxies
• The multiple coherence scales of C IV at cosmic noon