Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21543206d&link_type=abstract
American Astronomical Society, AAS Meeting #215, #432.06; Bulletin of the American Astronomical Society, Vol. 42, p.367
Astronomy and Astrophysics
Astronomy
Scientific paper
In recent years we have started to appreciate that the outskirts of galaxies contain valuable information about the formation process of galaxies. In hierarchical galaxy formation the stellar halos and thick disks of galaxies are thought to be the result of accretion of minor satellites, predominantly in the earlier assembly phases. The size, metallicity, and amount of substructure in current day halos are therefore directly related to issues like the small scale properties of the primordial power spectrum of density fluctuations and the suppression of star formation in small dark matter halos.
We will show highlights from our ongoing GHOSTS HST survey of the resolved stellar populations of 18 nearby, massive disk galaxies. We will show that the smaller galaxies (Vrot 100 km/s) have very small halos, but that most massive disk galaxies (Vrot 200 km/s) have very extended stellar envelopes. Structurally these envelopes are smoothly connected to the inner bulges and both components can be fitted by one Sersic profile. The envelope properties correlate with Hubble type and bulge-to-disk ratio. The color changes in the RGB star populations indicate that there are small radial metallicity gradients in these halos, but at 30 kpc above the disk the envelopes are still much more metal rich than the Milky Way halo. Given the structural and metallicity properties of the detected envelopes we may call into question whether we detect very extended bulge populations or inner halo populations.
de Jong Roelof
GHOSTS Collaboration
Radburn-Smith David J.
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