%0 Generic %1 bregman2013outflow %A Bregman, Joel N. %A Miller, Eric D. %A Seitzer, Patrick %A Cowley, C. R. %A Miller, Matthew J. %D 2013 %K absorption accretion feedback %T Outflow vs. Infall in Spiral Galaxies: Metal Absorption in the Halo of NGC 891 %U http://arxiv.org/abs/1304.0795 %X Gas accreting onto a galaxy will be of low metallicity while halo gas due to a galactic fountain will be of near-solar metallicity. We test these predictions by measuring the metal absorption line properties of halo gas 5 kpc above the plane of the edge-on galaxy NGC 891, using observations taken with HST/STIS toward a bright background quasar. Metal absorption lines of Fe II, Mg II, and Mg I in the halo of NGC 891 are clearly seen, and when combined with recent deep H I observations, we are able to place constraints on the metallicity of the halo gas for the first time. The H I line width defines the line broadening, from which we model opacity effects in these metal lines, assuming the absorbing gas is continuously distributed in the halo. The gas-phase metallicities are Fe/H = -1.18 +/- 0.07 and Mg/H = -0.23 +0.36/-0.27 (statistical errors) and this difference is probably due to differential depletion onto grains. When corrected for such depletion using Galactic gas as a guide, both elements have approximately solar or even supersolar abundances. This suggests that the gas is from the galaxy disk, probably expelled into the halo by a galactic fountain, rather than from accretion of intergalactic gas, which would have a low metallicity. The abundances would be raised by significant amounts if the absorbing gas lies in a few clouds with thermal widths smaller than the rotational velocity of the halo. If this is the case, both the abundances and Mg/Fe would be supersolar.

@misc{bregman2013outflow, abstract = {Gas accreting onto a galaxy will be of low metallicity while halo gas due to a galactic fountain will be of near-solar metallicity. We test these predictions by measuring the metal absorption line properties of halo gas 5 kpc above the plane of the edge-on galaxy NGC 891, using observations taken with HST/STIS toward a bright background quasar. Metal absorption lines of Fe II, Mg II, and Mg I in the halo of NGC 891 are clearly seen, and when combined with recent deep H I observations, we are able to place constraints on the metallicity of the halo gas for the first time. The H I line width defines the line broadening, from which we model opacity effects in these metal lines, assuming the absorbing gas is continuously distributed in the halo. The gas-phase metallicities are [Fe/H] = -1.18 +/- 0.07 and [Mg/H] = -0.23 +0.36/-0.27 (statistical errors) and this difference is probably due to differential depletion onto grains. When corrected for such depletion using Galactic gas as a guide, both elements have approximately solar or even supersolar abundances. This suggests that the gas is from the galaxy disk, probably expelled into the halo by a galactic fountain, rather than from accretion of intergalactic gas, which would have a low metallicity. The abundances would be raised by significant amounts if the absorbing gas lies in a few clouds with thermal widths smaller than the rotational velocity of the halo. If this is the case, both the abundances and [Mg/Fe] would be supersolar.}, added-at = {2013-04-04T17:30:05.000+0200}, author = {Bregman, Joel N. and Miller, Eric D. and Seitzer, Patrick and Cowley, C. R. and Miller, Matthew J.}, biburl = {https://www.bibsonomy.org/bibtex/2c37da2b0febea67ffcd4122b1720923e/miki}, description = {[1304.0795] Outflow vs. Infall in Spiral Galaxies: Metal Absorption in the Halo of NGC 891}, interhash = {9093ddf86da2f821908996c878632592}, intrahash = {c37da2b0febea67ffcd4122b1720923e}, keywords = {absorption accretion feedback}, note = {cite arxiv:1304.0795Comment: 24 pages, 4 figures}, timestamp = {2013-04-04T17:30:05.000+0200}, title = {Outflow vs. Infall in Spiral Galaxies: Metal Absorption in the Halo of NGC 891}, url = {http://arxiv.org/abs/1304.0795}, year = 2013 }