HST/COS Observations of the Warm Ionized Gaseous Halo of NGC 891

The metallicity of galactic gaseous halos provides insights into accretion and feedback of galaxies. The nearby edge-on galaxy NGC 891 has a multicomponent gaseous halo and a background active galactic nucleus (AGN; LQAC 035+042 003) projected 5 kpc above the disk near the minor axis. Against the UV continuum of this AGN, we detect lines from 13 ions associated with NGC 891 in new Hubble Space Telescope/Cosmic Origin Spectrograph spectra. Most of the absorption is from the warm ionized gas with log T = 4.22 +/- 0.04, log n(H) = -1.26 +/- 0.51, and log N-H = 20.81 +/- 0.20. The metallicity of volatile elements (i.e., C, N, and S) is about half solar ([X/H] approximate to -0.3 +/- 0.3), while Mg, Fe, and Ni show lower metallicities of [X/H] approximate to -0.9. The absorption system shows the depletion pattern seen for warm Galactic diffuse clouds, which is consistent with a mixture of ejected solar-metallicity disk gases and the hot X-ray-emitting halo (Z = 0.1-0.2 Z(circle dot)). The warm ionized gases are about five times more massive than the cold H I-emitting gases around the galactic center, which might lead to accretion with a mean rate of 10(2) M-circle dot yr(-1) for a period of time. We also detect low-metallicity (approximate to 0.1 Z(circle dot)) gases toward LQAC 035+042 003 at 110 km s(-1) (a high-velocity cloud) and toward another sight line (3C 66A; 108 kpc projected from NGC 891) at 30 km s(-1). This low-metallicity material could be the cold mode accretion from the intergalactic medium or the tidal disruption of satellites in the NGC 891 halo.