Chandra Detection of Local Warm – Hot Gas Toward Markarian 279

We report the Chandra detection of O VII Kα 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 H i 21-cm emission and O VI 1032Å 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 O VII absorption seen here, indicating that the O VII Doppler parameter is inconsistent with that of any low–velocity (Galactic thick disk) or high–velocity O VI (O VIHV) component. Direct association of the O VII with the O VIHV is further ruled out by the high temperatures required to produce the observed O VIHV/O VII ratio and the significant velocity difference between the O VII and O VIHV lines. If the O VII absorption is associated with a very broad, undetected O VI component, then the absorption must be broadened by primarily nonthermal processes. The large velocity dispersion and possible slight redshift of the O VII 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. Subject headings: intergalactic medium – X-rays: galaxies: clusters – cosmology: observations Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus OH 43210, USA Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, USA Instituto de Astronomía Universidad Autónomica de México, Apartado Postal 70-264, Ciudad Universitaria, México, D.F., CP 04510, México