On the discrepancy between the X-ray and UV absorption measurements of O VI in the local ISM
Abstract
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2019
- DOI:
- 10.1093/mnrasl/sly223
- arXiv:
- arXiv:1811.09280
- Bibcode:
- 2019MNRAS.483L..75G
- Keywords:
-
- ISM: atoms;
- ISM: abundances;
- ISM: structure;
- Galaxy: structure;
- X-rays: ISM;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 5 pages, 3 figures