| Type |
Journal Article |
| Names |
Alex S. Hill, L. Matthew Haffner, Ronald J. Reynolds |
| Publication |
The Astrophysical Journal |
| Volume |
703 |
| Issue |
2 |
| Pages |
1832-1838 |
| Date |
October 1, 2009 |
| URL |
http://adsabs.harvard.edu/abs/2009ApJ...703.1832H |
| Library Catalog |
NASA ADS |
| Abstract |
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 gsim3 × 106 M sun,
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. |
| Tags |
Galaxy: evolution, Galaxy: halo, ISM: ABUNDANCES, ISM: clouds, ISM: individual: Smith Cloud |