Dr. Cheng Li

This paper studied the optical-optical and optical-NIR color out to 8R_e for a sample of 673 massive early-type galaxies (ETGs) with M*>3×10^10 soloar mass, selected from SDSS-based SPIDER survey. Radial profiles of colors, as well as stellar age and metallicity derived from stellar population synthesis modelling are obtained. Generally, the outer regions are older and more metal-poor than the cores of the galaxies, and the trend is strongest for the most massive galaxies with M*>10^11 solar mass. Furthermore, the age gradient is more significant in ETGs residing in higher density environment. These results are consistent with the picture that the envelope of massive galaxies is made up of accreted small satellites (i.e. minor mergers) whose stars were born during the first stages of galaxy formation.

This paper studies the stellar halo of isolated central galaxies by stacking the HSC images. The sample covers a wide range of stellar mass, 9.2<lg(M*)<11.4, and out to radii of 120kpc. A strong self-similarity of the stellar halo profiles is found, albeit the large galaxy-to-galaxy scatter. Color profiles show a minimum at some radius, beyond which the color of the outer halo turns red again. This effect is most pronounced for the most massive galaxies in their sample.

The HSC images are used to probe the stellar halo of ~7000 massive galaxies at z~0.4.

This paper applied a stacking method to over 4000 galaxy clusters identified from the DES by the redMaPPer cluster finder to study the surface brightness of central galaxies and the intra-cluster light (ICL). The colour of the cluster central galaxy and ICL displays a radial gradient that becomes bluer at a larger radius, which is consistent with a stellar stripping and disruption origin of intra-cluster light as suggested by simulation studies.

The ICL is distinguished from the light of the galaxies in Comma and the fraction of ICL is obtained. The high ICL fractions and the excess in the bluer filters are indicative of a merging state. The presence of younger stars or stars with lower metallicity in the ICL suggests that the main mechanism of ICL formation for the Coma cluster is the stripping of the stars in the outskirts of infalling galaxies and possibly the disruption of dwarf galaxies during past or ongoing mergers.

The radial surface brightness profile of the BCG+ICL is best described by a double Sérsic model, with 68±4% of the H_E-band light contained in the extended, outer component. The transition between these components occurs at ≈50 kpc, beyond which the isophotes become increasingly elliptical and off-centered.The BCG+ICL colour becomes increasingly blue with radius, consistent with the stellar populations in the ICL having subsolar metallicities [Fe/H] ∼ −0.6. The colour of the ICL, and the specific frequency and luminosity function of the ICGCs suggest that the ICL+ICGCs were tidally stripped from the outskirts of massive satellites with masses of a few ×10^10 M⊙, with an increasing contribution from dwarf galaxies at large radii.