Stellar Halos of Massive Ellipticals
I have recently completed a large survey of nearby massive elliptical galaxies observed with the Mitchell Integral Field Spectrograph on the 2.5m Harlan Smith Telescope at McDonald (Greene et al. 2012, 2013). Our survey more than triples the number of spectral observations that extend to such large galactocentric distance. We find that the stars in the outskirts of massive ellipticals do not resemble the stars found in the centers of any local galaxies, at any mass (Greene et al. 2012). Instead, stars beyond two effective radii most resemble thick disk stars. They are old, with high [alpha/Fe] abundance ratios, low [Fe/H], and (intriguingly) high [N/Fe] (Greene et al. 2013). In other words, these stars were formed rapidly in shallow potential wells at z ~ 2, consistent with size growth via minor mergers with small satellites (e.g., Naab et al. 2009).
Princeton graduate student Sudhir Raskutti is looking for correlations between the stellar populations and kinematics at large radius.