2018ApJ...865...91S -
Astrophys. J., 865, 91-91 (2018/October-1)
Does circumgalactic O VI trace low-pressure gas beyond the accretion shock? Clues from H I and low-ion absorption, line kinematics, and dust extinction.
STERN J., FAUCHER-GIGUERE C.-A., HENNAWI J.F., HAFEN Z., JOHNSON S.D. and FIELDING D.
Abstract (from CDS):
Large O VI columns are observed around star-forming low-redshift ∼L* galaxies, with a dependence on impact parameter indicating that most O5+ particles reside beyond half the halo virial radius (≳100kpc). In order to constrain the nature of the gas traced by Ovi, we analyze additional observables of the outer halo, namely Hi to O VI column ratios of 1-10, an absence of low-ion absorption, a mean differential extinction of EB–V~10–3, and a linear relation between the O VI column and the O VI velocity width. We contrast these observations with two physical scenarios: (1) O VI traces high-pressure (∼30cm–3K) collisionally ionized gas cooling from a virially shocked phase, and (2) O VI traces low-pressure (≲1cm–3K) gas beyond the accretion shock, where the gas is in ionization and thermal equilibrium with the UV background. We demonstrate that the high-pressure scenario requires multiple gas phases to explain the observations and a large deposition of energy at ≳100kpc to offset the energy radiated by the cooling gas. In contrast, the low-pressure scenario can explain all considered observations with a single gas phase in thermal equilibrium, provided that the baryon overdensity is comparable to the dark-matter overdensity and that the gas is enriched to ≳Z☉/3 with an ISM-like dust-to-metal ratio. The low-pressure scenario implies that O VI traces a cool flow with a mass flow rate of ∼5M☉yr–1, comparable to the star formation rate of the central galaxies. The O VI line widths are consistent with the velocity shear expected within this flow. The low-pressure scenario predicts a bimodality in absorption line ratios at ∼100kpc, due to the pressure jump across the accretion shock.
Abstract Copyright:
© 2018. The American Astronomical Society. All rights reserved.
Journal keyword(s):
galaxies: halos - intergalactic medium - quasars: absorption lines
Simbad objects:
32
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