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2019MNRAS.483L..75G - Mon. Not. R. Astron. Soc., 483, L75-L79 (2019/February-2)

On the discrepancy between the X-ray and UV absorption measurements of O VI in the local ISM.


Abstract (from CDS):

The total amount of O VI present in the interstellar medium (ISM) obtained via absorption measurements in UV and X-ray spectra is currently in disagreement, with the latter being significantly larger (by a factor of 10 or more) than the former. Previous works have proposed that the blend of the O VI Kα line (22.032 Å) with the O II Kβ-L12 line (22.04 Å) could account for the stronger absorption observed in the X-ray spectra. Here, we present a detailed study of the oxygen absorption in the local ISM, implementing our new model IGMabs which includes photoabsorption cross-sections of highly ionized species of abundant elements as well as turbulence broadening. By analysing high-resolution Chandra spectra of 13 low-mass X-ray binaries (LMXBs) and 29 extragalactic sources, we have estimated the column densities of O I - O III and from O VI - O VIII along multiple line-of-sights. We find that in most cases the O II Kβ-L12 line accounts for <30 per cent of the total O VI K α + O II K β. We conclude that the amount of O II predicted by our model is still insufficient to explain the discrepancy between X-ray and UV measurements of O VI column densities.

Abstract Copyright: © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal keyword(s): ISM: atoms - ISM: abundances - ISM: structure - Galaxy: structure - X-rays: ISM

Simbad objects: 42

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