MNRAS 000, 1–19 (2018) Preprint 3 June 2022 Compiled using MNRAS L
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Origin of CGM OVI in cosmological simulations: redshift,
mass and radial dependence of collisional and photo
ionization
S. Roca-F` abrega
1,2 ?
, A. Dekel
2
, Y. Faerman
2
, O. Gnat
2
, C. Strawn
3
, D. Ceverino
4
,
J. Primack
3
, A. V. Macci` o
5,6
, A. A. Dutton
5
, J. X. Prochaska
7,8
, J. Stern
9
1
Departamento de F´ısica de la Tierra y Astrof´ısica, Facultad de Ciencias F´ısicas, Plaza Ciencias, 1, Madrid, E-28040, Spain
2
Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel
3
University of California, Santa Cruz, CA 95064, USA
4
Universit¨at Heidelberg, Zentrum f¨ ur Astronomie, Institut f¨ ur Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120, Heidelberg, Germany
5
New York University, Abu Dhabi, PO Box 129188, Saadiyat Island, Abu Dhabi, United Arab Emirates
6
Max-Planck-Institut f¨ ur Astronomie, K¨onigstuhl 17, D-69117, Heidelberg, Germany
7
Department of Astronomy and Astrophysics, UCO/Lick Ob- servatory, University of California, 1156 High Street, Santa Cruz, CA 95064, USA
8
Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8583, Japan
9
CIERA Fellow, Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL, USA
Accepted XXX. Received 08/2018; in original form 08/2018
ABSTRACT
We study the components of cool and warm/hot gas in the circumgalactic medium
(CGM) of simulated galaxies and address the relative production of OVI by photoion-
ization versus collisional ionization, as a function of halo mass, redshift, and distance
from the galaxy halo center. This is done utilizing two different suites of zoom-in hydro-
cosmological simulations, VELA and NIHAO, which yield consistent results despite
the different codes and different physical recipes for star formation and feedback.
We find that collisional ionization by thermal electrons dominates at high redshift,
while photoionization of cool or warm gas by the metagalactic radiation takes over
near z ∼ 2. In halos of ∼10
12
M
and above, collisions become important again at
z < 0.5, while photoionization remains significant down to z = 0 for less massive halos.
In halos with M > 3 × 10
11
M
, most of the photoionized gas at z ∼ 0 is in the warm
phase, just below the OVI peak (T . 3 × 10
5
K). We also find that collisions are
dominant in the central regions of halos, while photoionization is more significant at
the outskirts, around R
v
, even in massive halos. This too may be explained by the
presence of warm gas or, in lower mass halos, by cool gas inflows.
The position in redshift of the peak in the photoionized OVI fraction is depen-
dent on feedback implementation. In the future, observational estimation of the peak
redshift can be used to test feedback implementation in simulations. The penetration
of cool gas into the warm-hot CGM of high-mass halos also depends on the accretion
rate and feedback strength.
Key words: galaxies: evolution – galaxies: formation – methods: numerical
1 INTRODUCTION
Gas in the circumgalactic medium (CGM) is a key in-
gredient in galaxy evolution. Gas from the intergalactic
medium (IGM) streams into the centers of DM halos and
feeds star formation. Stellar feedback produces metallicity-
enhanced warm/hot gas (10
4.5
K<T<10
6.5
K) that outflows
to the CGM. Theory and simulations agree that halos
?
E-mail: sroca01@ucm.es
with M>M
crit
∼ 3 × 10
11
M
develop a warm/hot CGM
through both shock heating at ∼R
v
and outflows from
the disk. In these systems cold gas in narrow inflowing
streams can penetrate through warm/hot CGM only at
z > 2. In low mass halos (M<M
crit
), however, the CGM
is always dominated by cold (T<10
3.8
K) and cool gas
(10
3.8
K<T<10
4.5
K) (Birnboim & Dekel 2003; Kereˇs et al.
2005; Dekel & Birnboim 2006; Keres 2008; Correa et al.
2017). This implies that halos of mass ∼10
12
and above
should have a significant fraction of their baryons in a
© 2018 The Authors
arXiv:1808.09973v1 [astro-ph.GA] 29 Aug 2018