  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 \pm 3
degrees. HI observations give a rotation velocity of 108 kms and an atomic
hydrogen mass of M_{HI} = 3.1 X 10^9 d_{90}^2 \msun, where d_{90} 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 \pm 0.4) X 10^{21}
cm^{-2} assuming solar abundances. If the absorber is uniformly distributed
over the disk of the galaxy, the implied hydrogen mass is M_H = (6.2 \pm 1.2) X
10^8 d_{90}^2 \msun. 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.
