Comments on the manuscript: ``The weak absorbing outflow in AGN Mrk 279: evidence of super-solar metal abundances'' astro-ph/0611578 by Fields et al

Abstract

A recent manuscript posted on astro-ph (astro-ph/0611578) by Fields et al. (hereafter F06) reports evidence of supersolar metal abundances in Mrk 279 by analyzing its Chandra LETGS X-ray spectrum. We point out that it is impossible in principle to obtain direct metal abundances from these X-ray data, since there is no handle on the amount of hydrogen column density. If F06 would have lowered their C, N, O and Fe abundance by a factor of ten and increased the hydrogen column density by a factor of ten, they would have obtained an almost identical fit with subsolar metalicity. F06 find support for their supersolar metal abundances from a cursory analysis of the UV data from the same Mrk 279 campaign. We point out that F06 included in that analysis portions of the UV trough that are known to arise from gas unrelated to the outflow, which weakens the support from the UV data. A detailed analysis of the Chandra LETGS X-ray spectrum was accepted for publication in A&A on Sept 14 2006 (Costantini et al 2006; hereafter C06) and posted on astro-ph on the same date. F06 ignore most of this published analysis while duplicating the finding of two ionization components with similar parameters to the ones found by C06. Finally, we note that it is possible to derive accurate abundances from the UV data set of this object. We already published these findings in a conference precedings and have submitted the relevant manuscript to ApJ. We find that relative to solar the abundances in the Mrk 279 outflow are (linear scaling): carbon 2.2 +/- 0.7, nitrogen 3.5 +/- 1.1 and oxygen 1.6 +/- 0.8.