A Survey of Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope Sight Lines through High-Velocity Cloud Complex C
Abstract
Using archival Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) data, we have assembled a survey of eight sight lines through high-velocity cloud Complex C. Abundances of the observed ion species vary significantly for these sight lines, indicating that Complex C is not well characterized by a single metallicity. Reliable metallicities based on [O I/H I] range from 0.1 to 0.25 Zsolar. Metallicities based on [S II/H I] range from 0.1 to 0.6 Zsolar, but the trend of decreasing abundance with H I column density indicates that photoionization corrections may affect the conversion to [S/H]. We present models of the dependence of the ionization correction on H I column density; these ionization corrections are significant when converting ion abundances to elemental abundances for S, Si, and Fe. The measured abundances in this survey indicate that parts of the cloud have a higher metallicity than previously thought and that Complex C may represent a mixture of ``Galactic fountain'' gas with infalling low-metallicity gas. We find that [S/O] and [Si/O] have a solar ratio, suggesting little dust depletion. Further, the measured abundances suggest an overabundance of O, S, and Si relative to N and Fe. The enhancement of these α-elements suggests that the bulk of the metals in Complex C were produced by Type II supernovae and then removed from the star-forming region, possibly via supernova-driven winds or tidal stripping, before the ISM could be enriched by N and Fe.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2003
- DOI:
- 10.1086/345949
- arXiv:
- arXiv:astro-ph/0209229
- Bibcode:
- 2003ApJ...585..336C
- Keywords:
-
- Galaxy: Halo;
- ISM: Abundances;
- ISM: Clouds;
- Galaxies: Quasars: Absorption Lines;
- Astrophysics
- E-Print:
- 50 pages, 17 figures. Accepted to ApJ. Previous version was the first submitted manuscript