The information content of stellar halos: Stellar population gradients and accretion histories in early-type Illustris galaxies

摘要: Long dynamical timescales in the outskirts of galaxies preserve information content their accretion histories, for example form stellar population gradients. We present a detailed analysis halo properties statistically representative sample early-type from Illustris simulation and show that gradients at large radii can indeed be used to infer basic galactic histories. measure metallicity, age, surface-brightness profiles quiescent ranging $\mathrm{M}_\star = 10^{10} - 2\times 10^{12}\;\mathrm{M}_\odot$ they are reasonable agreement with observations. At fixed mass, accreted little material tend have steeper metallicity between 2 4 effective (R$_e$) than those larger fractions. Profiles typically flatten z 1 present. This suggests stars into tends profiles, picture which is supported by tight correlation two halo. find no statistical evidence additional related histories beyond what contained profiles. Age do not appear sensitive none studied strongly correlated mean merger mass-ratio. Future observations reach outside will best potential constrain