Constraints on hot metals in the Vicinity of the Galaxy

Abstract

We have searched for evidence of soft X-ray absorption by hot metals in the vicinity of the Galaxy in the spectra of a small sample of fifteen Type I AGN observed with the high resolution X-ray gratings on board Chandra. This is an extension of our previous survey of hot OVII and OVIII absorbing gas in the vicinity of the Galaxy. The strongest absorption signatures within a few hundred km/s of their rest-frame energies are most likely due to warm absorbing outflows from the nearest AGN, which are back-lighting the local hot gas. We emphasize that absorption signatures in the spectra of some distant AGN that are kinematically consistent with the recessional velocity of the AGN are most likely to be due to hot local gas. Along the sightline towards PG 1211+143, PDS 456 and MCG-6-30-15 there is a very large absorbing Fe column density which is kinematically consistent with absorption by hot, local Fe. The sightlines to these three AGN pass through the limb of the Northern Polar Spur (NPS), a local bubble formed from several supernovae which, if rich in Fe, may account for a large local Fe column. We obtain limits on the column density of local, highly ionized N, Ne, Mg, Si along all of the sightlines in our sample. We correlate the column density limits with those of highly ionized O along the same sightlines. Assuming the hot local gas is in collisionally ionized equilibrium, we obtain limits on the temperature and relative abundances of the metals in the hot local gas. Our limits on the ionic column densities in the local hot gas seem to be consistent with those observed in the hot halo gas of edge-on normal spiral galaxies.

arXiv comment9 pages,2 figures, MNRAS (accepted)

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