Dual Stellar Halos in the Standard Elliptical Galaxy M105 and Formation
  of Massive Early-Type Galaxies
  M105 is a standard elliptical galaxy, located in the Leo I Group. We present
photometry of the resolved stars in its inner region at R ~ 4' ~ 4Reff,
obtained from F606W and F814W images in the Hubble Space Telescope archive. We
combine this with photometry of the outer region at R ~ 12' ~ 12Reff from
archival imaging data. Color-magnitude diagrams of the resolved stars in the
inner region show a prominent red giant branch (RGB) with a large color range,
while those of the outer region show better a narrow blue RGB. The metallicity
distribution function (MDF) of the RGB stars shows the existence of two
distinct subpopulations: a dominant metal-rich population (with a peak at [M/H]
~ 0.0) and a much weaker metal-poor population (with a peak at [M/H] ~ -1.1).
The radial number density profiles of the metal-rich and metal-poor RGB stars
are fit well by a Sersic law with n=2.75+-0.10 and n=6.89+-0.94, and by a
single power law, respectively. The MDFs of the inner and outer regions can be
described well by accretion gas models of chemical evolution with two
components. These provide strong evidence that there are two distinct stellar
halos in this galaxy, metal-poor and red metal-rich halos, consistent with the
results based on globular cluster systems in bright early-type galaxies (Park &
Lee 2013). We discuss the implications of these results with regard to the
formation of massive early-type galaxies in the dual halo mode formation
scenario.
