Astrophys. J., 703, 1832-1838 (2009/October-1)
Ionized gas in the Smith Cloud.
HILL A.S., HAFFNER L.M. and REYNOLDS R.J.
Abstract (from CDS):
We present Wisconsin Hα Mapper observations of ionized gas in the Smith Cloud, a high-velocity cloud which Lockman et al. have recently suggested is interacting with the Galactic disk. Our Hα map shows the brightest Hα emission, 0.43±0.04 R, coincident with the brightest H I, while slightly fainter Hα emission (0.25±0.02 R) is observed in a region with H I intensities <0.1 times as bright as the brightest H I. We derive an ionized mass of ≳3x106 M☉, comparable to the H I mass, with the H+ mass spread over a considerably larger area than that of H I. An estimated Galactic extinction correction could adjust these values upward by 40%. Hα and [S II] line widths toward the region of brightest emission constrain the electron temperature of the gas to be between 8000 K and 23,000 K. A detection of [N II] λ6583 in the same direction with a line ratio [N II]/Hα = 0.32±0.05 constrains the metallicity of the cloud: for typical photoionization temperatures of 8000-12,000 K, the nitrogen abundance is 0.15-0.44 times solar. These results lend further support to the claim that the Smith Cloud is new material accreting onto the Galaxy.
Galaxy: evolution - Galaxy: halo - ISM: abundances - ISM: clouds - ISM: individual: Smith Cloud
Fig. 3, Table 2: [HHR2009] Clump A (Nos A-B), [HHR2009] Tip N=1, [HHR2009] Tail N=1.
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