Mathematics – Logic
Scientific paper
Jul 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12213d&link_type=abstract
HST Proposal ID #12213. Cycle 18
Mathematics
Logic
Scientific paper
Stellar halos surrounding massive galaxies are of prime interest in hierarchical galaxyformation models: most of the halo is formed by the very early accretion of small, metalpoor satellite galaxies each with their independent evolution history. As such, haloscontain the fossil remnants of the earliest star formation and accretion phases of agalaxy in formation. The resulting size, shape, age, and metallicity of stellar halosprovide therefore a direct test of the basic ingredients {reionization, feedback from starformation, density fluctuation power spectrum} of hierarchical galaxy formation models.In our GHOSTS survey we have sampled the principle axes of a sample of 11 nearby galaxieswith Vrot>100 km/s. Our detection of resolved stellar halo populations 1.5 mag below thetip of the Red Giant Branch has revealed halos that extend as far as 30 kpc around themost massive galaxies in our sample. Those extended stellar halos seem more compact thancurrent model predictions, they have unexpectedly high metallicity up to the last detectedpoint, and have a luminosity that is more closely related to the bulge luminosity than tothe galaxy mass. We propose to extend the light profiles of 4 massive galaxies with arange in bulge-to-disk ratio to the background limit at 70 kpc. This will enable us to: - confirm the stellar halo shape {compactness} and assess with confidence any conflict with models using these very extended and accurate halo profile characterizations; - establish whether stellar envelopes beyond 30 kpc are still morphologically connected to inner bulges, or whether a break occurs at larger radii revealing a distinct new component; - determine whether every massive galaxy has an old, metal-poor halo at large radius like the Milky Way and M31; if not, constrain for the first time the range of stellar metallicity gradients in extended stellar halos.;
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