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Bimodality of low-redshift circumgalactic O vi in non-equilibrium eagle zoom simulations

Oppenheimer, BD and Crain, RA and Schaye, J and Rahmati, A and Richings, AJ and Trayford, JW and Tumlinson, J and Bower, RG and Schaller, M and Theuns, T (2016) Bimodality of low-redshift circumgalactic O vi in non-equilibrium eagle zoom simulations. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 460 (2). pp. 2157-2179. ISSN 0035-8711

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Abstract

We introduce a series of 20 cosmological hydrodynamical simulations of L⇤
(M200 = 1011.7 − 1012.3M") and group-sized (M200 = 1012.7 − 1013.3M") haloes run with the model used for the EAGLE project, which additionally includes a nonequilibrium ionization and cooling module that follows 136 ions. The simulations reproduce the observed correlation, revealed by COS-Halos at z ⇠ 0.2, between Ovi column density at impact parameters b < 150 kpc and the specific star formation rate (sSFR⌘SFR/M⇤) of the central galaxy at z ⇠ 0.2. We find that the column density of circumgalactic Ovi is maximal in the haloes associated with L⇤ galaxies, because their virial temperatures are close to the temperature at which the ionization fraction of Ovi peaks (T ⇠ 105.5 K). The higher virial temperature of group haloes (> 106 K) promotes oxygen to higher ionization states, suppressing the Ovi column density.
The observed NOvi-sSFR correlation therefore does not imply a causal link, but reflects the changing characteristic ionization state of oxygen as halo mass is increased.
In spite of the mass-dependence of the oxygen ionization state, the most abundant circumgalactic oxygen ion in both L⇤ and group haloes is Ovii; Ovi accounts for only 0.1% of the oxygen in group haloes and 0.9-1.3% with L⇤ haloes. Nonetheless, the metals traced by Ovi absorbers represent a fossil record of the feedback history of galaxies over a Hubble time; their characteristic epoch of ejection corresponds to z > 1 and much of the ejected metal mass resides beyond the virial radius of galaxies.
For both L⇤ and group galaxies, more of the oxygen produced and released by stars resides in the circumgalactic medium (within twice the virial radius) than in the stars and ISM of the galaxy.

Item Type: Article
Additional Information: This article has been accepted for publication in MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY ©:2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: OXFORD UNIV PRESS
Related URLs:
Date Deposited: 19 Sep 2016 08:35
Last Modified: 07 Sep 2017 15:06
DOI or Identification number: 10.1093/mnras/stw1066
URI: http://researchonline.ljmu.ac.uk/id/eprint/4170

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