2012ApJ...761..145B -
Astrophys. J., 761, 145 (2012/December-3)
Present-day galactic evolution: low-metallicity, warm, ionized gas inflow associated with high-velocity cloud complex A.
BARGER K.A., HAFFNER L.M., WAKKER B.P., HILL A.S., MADSEN G.J. and DUNCAN A.K.
Abstract (from CDS):
The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin Hα Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km/s in the local standard of rest reference frame. These observations include the first full Hα intensity map of Complex A across (l,b)=(124°, 18°) to (171°, 53°) and deep targeted observations in Hα, [S II] λ6716, [N II] λ6584, and [O I] λ6300 toward regions with high H I column densities, background quasars, and stars. The Hα data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 106 M☉. We find that the Bland-Hawthorn & Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 104 K or for gas with a high fraction of singly ionized nitrogen and sulfur.
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Journal keyword(s):
Galaxy: evolution - Galaxy: halo - ISM: abundances - ISM: atoms - ISM: individual: Complex A
Simbad objects:
25
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