The nature and origins of the low surface brightness outskirts of massive, central galaxies in Subaru HSC

We explore the stellar mass density and colour profiles of 118 low redshift, massive, central galaxies, selected to have assembled 90 per cent of their stellar mass 6 Gyr ago, finding evidence of the minor merger activity expected to be the driver behind the size growth of quiescent galaxies. We use imaging data in the g , r , i, z, y bands from the Subaru Hyper Suprime-Cam survey and perform SED fitting to construct spatially well-resolved radial profiles in colour and stellar mass surface density. Our visual morphological classification reveals that similar to 42 per cent of our sample displays tidal features, similar to previous studies, similar to 43 per cent of the remaining sample displays a diffuse stellar halo, and only similar to 14 per cent displays no features, down to a limiting mu(r-band) similar to 28 mag arcsec (-2). We find good agreement between the stacked colour profiles of our sample to those derived from previous studies and an expected smooth, declining stellar mass surface density profile in the central regions (< 3 R-e). However, we also see a flattening of the profile (Sigma(*) similar to 10(7.5) M-circle dot kpc(-2)) in the outskirts (up to 10 R-e), which is revealed by our method of specifically targeting tidal/accretion features. We find similar levels of tidal features and behaviour in the stellar mass surface density profiles in a younger comparison sample, ho we ver, a lack of dif fuse haloes. We also apply stacking techniques similar to those in previous studies, finding such procedures wash out tidal features and thereby produce smooth declining profiles. The stellar material in the outskirts contributes on average similar to 10(10) M-? or a few per cent of the total stellar mass and has similar colours to SDSS satellites of similar stellar mass.

Automated summary

We examine the stellar mass density and color profiles of a sample of 118 central galaxies at low redshift. We find evidence of minor mergers, supporting the idea that these mergers drive the growth of quiescent galaxies. Using imaging data and SED fitting, we construct spatially resolved radial profiles. Our analysis reveals tidal features in about 42% of the sample, a diffuse stellar halo in 43%, and no features in 14%. We observe a flattening of the profile in the outskirts, providing further support for the role of minor mergers.