CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: Dependence on redshift, halo mass, and radius

S. Roca-Fàbrega*, A. Dekel, Y. Faerman, O. Gnat, C. Strawn, D. Ceverino, J. Primack, A. V. Macciò, A. A. Dutton, J. X. Prochaska, J. Stern

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


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 photoionization versus collisional ionization, as a function of halo mass, redshift, and distance from the galaxy halo centre. This is done utilizing two different suites of zoom-in hydro-cosmological simulations, VELA (6 haloes; z > 1) and NIHAO (18 haloes; to z = 0), which provide a broad theoretical basis because they use different codes and physical recipes for star formation and feedback. In all haloes studied in this work, 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 haloes of ∼1012 M and above, collisions become important again at z < 0.5, while photoionization remains significant down to z = 0 for less massive haloes. In haloes with Mv > 3 × 1011 M, at z ∼ 0 most of the photoionized OVI is in a warm, not cool, gas phase (T 3 × 105 K). We also find that collisions are dominant in the central regions of haloes, while photoionization is more significant at the outskirts, around Rv, even in massive haloes. This too may be explained by the presence of warm gas or, in lower mass haloes, by cool gas inflows.

Original languageEnglish
Pages (from-to)3625-3645
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - 11 Apr 2019
Externally publishedYes


FundersFunder number
DFG/DIPSTE 1869/2-1 GE 625/17-1
PBC/ISFGIF I-1341-303.7/2016, BSF 2014-273, 1829/12, PICS 2015-18
Spanish Ministry of Economy and Competitiveness
National Science FoundationAST-1405962
Council of State and Territorial Epidemiologists1869/2-1 GE 625/17-1
H2020 European Research Council
Seventh Framework Programme1405962, 339177
Pacific Institute for Climate Solutions2015-18
Comunidad de Madrid
Royal Society of Canada
British Skin Foundation2014-273
European Research Council
German-Israeli Foundation for Scientific Research and DevelopmentI-1341-303.7/2016
Ministerio de Economía y CompetitividadAYA2016-75808-R
Israel Science Foundation124/12
Consejería de Sanidad, Comunidad de Madrid2017-T2/TIC-5592
National Science Foundation


    • Galaxies: evolution
    • Galaxies: formation
    • Methods: numerical


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