Extended OVI haloes of starforming galaxies

Abstract

We consider evolution of metal-enriched gas exposed to a superposition of time-dependent radiation field of a nearby starburst galaxy and nearly invariant (on timescales 100 Myr) extragalactic ionization background. Within nonequilibrium (time-dependent) photoionization models we determine ionization fraction of the OVI ion commonly observed in galactic circumference. We derive then conditions for OVI to appear in absorptions in extended galactic haloes depending on the galactic mass and star formation rate. We have found that the maximum OVI fraction can reach $\sim 0.4-0.9$ under combined action of the galactic and the extragalactic ionizing radiation fields. We conclude that soft X-ray emission with $E\simgt 113$~eV from the stellar population of central starforming galaxies is the main source of such a high fraction of OVI. This circumstance can explain high column densities $\mathrm{N}(\mathrm{OVI})\sim 10^{14.5-15.3}$~cm${}^{-2}$ observed in the haloes of starforming galaxies at low redshifts (Tumlinson etal 2011) {\it even} for a relatively low ({ $\sim 0.01-0.1\zsun$}) metallicity. As a result, the requirements to the sources of oxygen in the extended haloes relax to a reasonably conservative level. We show that at $z\simlt 0.5$ ionization kinetics of oxygen in a relatively dense plasma $n\simgt 10^{-4}$ cm${}^{-3}$ of outer halo exposed to a low extragalactic ionizing flux is dominated by nonequilibrium effects.

12 pages, 11 figures, matches the version accepted in MNRAS

References in corpus (9)

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Cited by in corpus (11)

• Bimodality of low-redshift circumgalactic O VI in non-equilibrium EAGLE zoom simulations
• The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies
• The abundance, distribution, and physical nature of highly ionized oxygen OVI, OVII, and OVIII in IllustrisTNG
• Galactic and Circumgalactic OVI and its Impact on the Cosmological Metal and Baryon Budgets at 2<z<3.5
• Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos
• On the OVI Abundance in the Circumgalactic Medium of Low-Redshift Galaxies
• The extent of chemically enriched gas around star-forming dwarf galaxies
• Does circumgalactic OVI trace low-pressure gas beyond the accretion shock? Clues from HI and low-ion absorption, line kinematics, and dust extinction
• CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass and radius
• On the connection between the metal-enriched intergalactic medium and galaxies: an OVI-galaxy cross-correlation study at $z<1$
• Ionization Modeling Astrophysical Gaseous Structures. I. The Optically Thin Regime