Chandra Detection of Local Warm-Hot Gas Toward Markarian 279

Abstract

We report the Chandra detection of OVII K\alpha absorption at z=0 in the direction of the z=0.03 Seyfert 1 galaxy Mkn 279. The high velocity cloud Complex C lies along this line of sight, with HI 21-cm emission and OVI 1032\AA absorption both observed at velocities of ~ -150 km/s relative to the local standard of rest. We present an improved method for placing limits on the Doppler parameter and column density of a medium when only one unresolved line can be measured; this method is applied to the OVII absorption seen here, indicating that the OVII Doppler parameter is inconsistent with that of any low-velocity (Galactic thick disk) or high-velocity OVI (OVI_HV) component. Direct association of the OVII with the OVI_HV is further ruled out by the high temperatures required to produce the observed OVI_HV/OVII ratio and the significant velocity difference between the OVII and OVI_HV lines. If the OVII absorption is associated with a very broad, undetected OVI component, then the absorption must be broadened by primarily nonthermal processes. The large velocity dispersion and possible slight redshift of the OVII absorption (as well as limits on the absorber's temperature and density) may be indicative of a local intergalactic medium origin, though absorption from a hot, low-density Galactic corona cannot be ruled out.Comment: 20 pages including 5 figures, 1 table; minor changes to text/figures, accepted to Ap