SIMBAD references

2017ApJ...851L...7M - Astrophys. J., 851, L7-L7 (2017/December-2)

The O VI mystery: mismatch between X-ray and UV column densities.


Abstract (from CDS):

The UV spectra of Galactic and extragalactic sightlines often show O VI absorption lines at a range of redshifts, and from a variety of sources from the Galactic circumgalactic medium to active galactic nuclei (AGN) outflows. Inner shell O VI absorption is also observed in X-ray spectra (at λ=22.03 Å), but the column density inferred from the X-ray line was consistently larger than that from the UV line. Here we present a solution to this discrepancy for the z = 0 systems. The O II Kβ line 4S0→(3D)3p4P at 562.40 eV (≡22.04 Å) is blended with the O VI Kα line in X-ray spectra. We estimate the strength of this O II line in two different ways, and show that in most cases the O II line accounts for the entire blended line. The small amount of O VI equivalent width present in some cases has column density entirely consistent with the UV value. This solution to the O VI discrepancy, however, does not apply to high column-density systems like AGN outflows. We discuss other possible causes to explain their UV/X-ray mismatch. The O VI and O II lines will be resolved by gratings on board the proposed mission Arcus and the concept mission Lynx, and would allow the detection of weak O VI lines not just at z = 0, but also at higher redshift.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): atomic data - atomic processes - Galaxy: halo - line: identification - quasars: absorption lines - X-rays: general - X-rays: general

CDS comments: Table 1: E 181+643 was not identified.

Simbad objects: 69

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