{\it HST}/COS Observations of the Warm Ionized Gaseous Halo of NGC 891

Zhijie Qu; Joel N. Bregman; Edmund J. Hodges-Kluck

doi:10.3847/1538-4357/ab17df

paper

{\it HST}/COS Observations of the Warm Ionized Gaseous Halo of NGC 891

arXiv:1904.04716 · doi:10.3847/1538-4357/ab17df

Abstract

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 {\it HST}/COS spectra. Most of the absorption is from the warm ionized gas with $lo g T = 4.22 \pm 0.04$ , $lo g n_{H} = - 1.26 \pm 0.51$ , and $lo g N_{H} = 20.81 \pm 0.20$ . 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 ( $Z = 0.1 - 0.2 Z_{⊙}$ ). The warm ionized gases are about 5 times more massive than the cold \ion{H}{1} emitting gases around the galactic center, which might lead to accretion with a mean rate of $1 0^{2} M_{⊙} y r^{- 1}$ for a period of time. We also detect low metallicity ( $\approx 0.1 Z_{⊙}$ ) 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.

arXiv comment17 pages, 9 figures, accepted by ApJ

{\it HST}/COS Observations of the Warm Ionized Gaseous Halo of NGC 891

Abstract

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