DETECTION OF CA-II ABSORPTION IN THE QSO.0958+559 DUE TO A HEILES SHELL IN NGC-3079

We present optical observations of the QSO 0958 + 559 (z(e) = 1.154, m(B) = 18.4) and the nearby, edge-on spiral galaxy NGC 3079 [SB(s)c(spindle), z(sys) = 0.00375]. Spectra of the QSO show Ca II absorption lines due to extended gas in NGC 3079; the Na I absorption lines due to NGC 3079 are not detected. An unrelated, higher redshift absorption system at z(abs) = 1.1327 is also present in the QSO spectrum. The close proximity on the sky of this QSO to NGC 3079 makes it particularly suited for an absorption-line study of this kind. NGC 3079 is a well-studied galaxy with remarkable global and nuclear properties including the presence of a nuclear "superwind" and extended H I emission in the form of Heiles shells. The QSO sightline shines directly through one such Helies shell. The coincidence in position coupled with the agreement between the Ca II absorption and shell emission velocities demonstrates that the QSO absorption system is due to gas in this shell. The QSO and galaxy nucleus are separated on the plane of the sky by 2'.4, or a projected distance of 7.9 h-1 kpc (h = H0/100 km s-1 Mpc-1). Due to the high inclination of NGC 3079 coupled with the QSO and gas shell configuration, a more pertinent measure of the QSO-galaxy separation is the distance, measured perpendicular to the disk plane, between the QSO and the major axis. This height is 4.9 h-1 kpc. A broad-band band, blue CCD image of the field shows that the QSO sightline and the nearby rim of the Heiles (H I 21 cm) shell are far from the optical extent of NGC 3079 (at 25 B-mag arcsec-2). Because the Na I lines due to NGC 3079 are not detected, only a lower limit to the column density ratio is measured at N(Ca II)/N(Na I) > 4.7. This large lower limit suggests that calcium is not strongly depleted onto grains; it is not consistent with absorption by disklike gas. The moderate metallicity of the absorbing gas, N(Ca II)/N(H I) = 12 +/- 5 x 10(-9), is like that seen primarily in intermediate-velocity clouds in the Galaxy and in the Magellanic Stream. Based on the H I column density, N(H I) = 4.8 +/- 2.0 x 10(20) cm-2, this system would be characterized as a damped Lyman alpha absorber, yet the sightline does not shine through the disk of NGC 3079. We briefly discuss this system in comparison with the six other low-redshift QSO-galaxy pair absorption systems, and we speculate on the influence of Heiles shells to the interpretation of higher redshift QSO absorption systems.