GHOSTS | Bulges, Halos, and the Resolved Stellar Outskirts of Massive Disk Galaxies

Details GHOSTS | Bulges, Halos, and the Resolved Stellar Outskirts of Massive Disk Galaxies GHOSTS | Bulges, Halos, and the Resolved Stellar Outskirts of Massive Disk Galaxies

2007-10-29

arxiv.org/abs/0710.5511v1

Astronomy and Astrophysics

Astrophysics

4 pages, 2 figures. To appear in the proceedings of "The Formation and Evolution of Galaxy Disks", Rome 2007, editors J. G. Fu

Scientific paper

In hierarchical galaxy formation the stellar halos of galaxies are formed by the accretion of minor satellites and therefore contain valuable information about the (early) assembly process of galaxies. Our GHOSTS survey measures the stellar envelope properties of 14 nearby disk galaxies by imaging their resolved stellar populations with HST/ACS&WFPC2. Most of the massive galaxies in the sample (Vrot>200 km/s) have very extended stellar envelopes with mu(r) ~ r^{-2.5} power law profiles in the outer regions. For these massive galaxies there is some evidence that the stellar surface density of the profiles correlates with Hubble type and bulge-to-disk ratio, begging the question whether these envelopes are more related to bulges than to a Milky Way-type stellar halo. Smaller galaxies (Vrot 100 km/s) have much smaller stellar envelopes, but depending on geometry, they could still be more luminous than expected from satellite remnants in hierarchical galaxy formation models. Alternatively, they could be created by disk heating through the bombardment of small dark matter sub-halos. We find that galaxies show varying amounts of halo substructure.

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