The metallicity of galactic gaseous halos provides insights into accretion and feedback of galaxies .
The nearby edge-on galaxy NGC 891 has a multi-component gaseous halo and a background 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 HST /COS spectra .
Most of the absorption is from the warm ionized gas with \log T = 4.22 \pm 0.04 , \log n _ { H } = -1.26 \pm 0.51 , and \log N _ { H } = 20.81 \pm 0.20 .
The metallicity of volatile elements ( i.e. , C , N , and S ) is about half solar ( [ X / H ] \approx - 0.3 \pm 0.3 ) , while Mg , Fe , and Ni show lower metallicities of [ X / H ] \approx - 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 _ { \odot } ) .
The warm ionized gases are about 5 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 _ { \odot } ~ { } yr ^ { -1 } for a period of time .
We also detect low metallicity ( \approx 0.1 ~ { } Z _ { \odot } ) 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 IGM or the tidal disruption of satellites in the NGC 891 halo .