Soft X-ray Absorption Due to a Foreground Edge-on Spiral Galaxy toward the Core of Abell 2029

We have detected an X-ray absorption feature against the core of the galaxy cluster Abell 2029 (z = 0.0767) which we identify with the foreground galaxy UZC J151054.6+054313 (z = 0.0221). Optical observations (B, V , R, and I) indicate that it is an Scd galaxy seen nearly edge-on at an inclination of 87±3. H i observations give a rotation velocity of 108 km s and an atomic hydrogen mass of MHI = 3.1× 10 d90 M⊙, where d90 is the distance to the galaxy in units of 90 Mpc. X-ray spectral fits to the Chandra absorption feature yield a hydrogen column density of (2.0± 0.4)× 10 cm assuming solar abundances. If the absorber is uniformly distributed over the disk of the galaxy, the implied hydrogen mass is MH = (6.2± 1.2)× 10 d90 M⊙. Since the absorbing gas in the galaxy is probably concentrated to the center of the galaxy and the middle of the disk, this is a lower limit to the total hydrogen mass. On the other hand, the absorption measurements imply that the dark matter in UZC J151054.6+054313 is not distributed in a relatively uniform diffuse gas. Subject headings: dark matter — galaxies: clusters: individual (Abell 2029) — galaxies: individual (UZC J151054.6+054313) — galaxies: spiral — radio lines: galaxies — X-rays: galaxies