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Soft X-ray and ultraviolet metal-line emission from the gas around galaxies

van de Voort, Freeke and Schaye, Joop 2013. Soft X-ray and ultraviolet metal-line emission from the gas around galaxies. Monthly Notices of the Royal Astronomical Society 430 (4) , pp. 2688-2702. 10.1093/mnras/stt115

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Abstract

A large fraction of the gas in galactic haloes has temperatures between 104.5 and 107 K. At these temperatures, cooling is dominated by metal-line emission if the metallicity Z ≳ 0.1 Z⊙, and several lines may be detectable with current and upcoming instruments. We explore this possibility using several large cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations project. We stack surface brightness maps centred on galaxies to calculate the expected mean surface brightness profiles for different halo masses. We only consider emission from intergalactic gas with densities nH < 0.1 cm−3. Results are shown for soft X-ray lines at z = 0.125, ultraviolet (UV) lines and hydrogen Balmer-α (Hα) at z = 0.25, and rest-frame UV lines at z = 3. Assuming a detection limit of 10−1 photon s−1 cm−2 sr−1, proposed X-ray telescopes can detect O viii emission from z = 0.125 out to 80 per cent of the virial radius (Rvir) of groups and clusters and out to 0.4Rvir for haloes with masses 1012−13 M⊙. Emission lines from C vi, N vii, O vii and Ne x can be detected out to smaller radii, 0.1−0.5Rvir. With a detection limit of 10−20 erg s−1 cm−2 arcsec−2, future UV telescopes can detect C iii emission out to 0.2–0.6Rvir at z = 0.25, depending on halo mass. C iv, O vi, Si iii and Si iv can be seen out to 10–20 per cent of the virial radius in haloes more massive than 1012 M⊙. Optical Hα emission is comparable in strength to C iii emission and could be observed out to 0.3–0.6Rvir at z = 0.25 with upcoming optical instruments. At z = 3, it may be possible to observe C iii out to 0.2–0.3Rvir and other rest-frame UV lines out to ∼0.1Rvir in haloes larger than 1011 M⊙ with the same optical instruments. Metal-line emission is typically biased towards high density and metallicity and towards the temperature at which the emissivity curve of the corresponding metal-line peaks. This bias varies with radius, halo mass and redshift. The bias is similar for the different soft X-ray lines considered, whereas it varies strongly between different UV lines. Active galactic nucleus feedback can change the inner surface brightness profiles significantly, but it generally does not change the radius out to which the emission can be observed. Metal-line emission is a promising probe of the warm and hot, enriched gas around galaxies and provides a unique window into the interactions between galaxies and their gaseous haloes.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 12 March 2020
Date of Acceptance: 8 January 2013
Last Modified: 12 Mar 2020 15:00
URI: http://orca.cardiff.ac.uk/id/eprint/130257

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