Halos of Spiral Galaxies. II. Halo Metallicity-Luminosity Relation
Abstract
Using the Hubble Space Telescope, we have resolved individual red giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look at the systematic trends in halo stellar populations. We have found that bright galaxies tend to have broad red giant branch star color distributions with redder mean colors, suggesting that the heavy-element abundance spread increases with the parent galaxy luminosity. The mean metallicity of the stellar halo, estimated using the mean colors of red giant branch stars, correlates with the parent galaxy luminosity. The metallicity of the Milky Way halo falls nearly 1 dex below this luminosity-metallicity relation, suggesting that the halo of the Galaxy is more the exception than the rule for spiral galaxies; i.e., massive spirals with metal-poor halos are unusual. The luminosity-halo stellar abundance relation is consistent with the scaling relation expected for stellar systems embedded in dominant halos, suggesting that the bulk of the halo stellar population may have formed in situ.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.- Publication:
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The Astrophysical Journal
- Pub Date:
- November 2005
- DOI:
- 10.1086/468178
- arXiv:
- arXiv:astro-ph/0510254
- Bibcode:
- 2005ApJ...633..821M
- Keywords:
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- Galaxies: Formation;
- Galaxies: Halos;
- Galaxies: Individual: NGC Number: NGC 55;
- Galaxies: Individual: NGC Number: NGC 247;
- Galaxies: Individual: NGC Number: NGC 253;
- Galaxies: Individual: NGC Number: NGC 300;
- Galaxies: Individual: NGC Number: NGC 3031;
- Galaxies: Individual: NGC Number: NGC 4244;
- Galaxies: Individual: NGC Number: NGC 4945;
- Galaxies: Individual: NGC Number: NGC 5248;
- Galaxies: Stellar Content;
- Astrophysics
- E-Print:
- 10 pages, 5 figures (ApJ, in press)