The stellar mass structure of massive galaxies from z=0 to z=2.5; surface density profiles and half-mass radii

Knowledge of the mass distribution within galaxies is essential for our understanding of their structure, but is challenging to acquire due to the complex spatial distribution of stellar populations. The advent of deep, high-resolution data over a wide range of wavelengths provides an unprecedented opportunity to measure spatial variations in stellar populations and quantify their effects on the mass-to-light distribution. In this Paper we present stellar mass surface density profiles of a mass-selected sample of galaxies at 0 < z < 2.5, obtained using very deep HST optical and near-infrared data. This is the first time accurate stellar mass surface density profiles have been measured for galaxies up to z=2.5. The profiles are constructed using radial rest-frame u-g color profiles, from which we derive the stellar mass-to-light ratio as a function of radius. The key advantage of this study compared to previous work is that the profiles are deconvolved for PSF smoothing, allowing accurate measurements of high-redshift galaxy structure. The profiles are obtained using a measurement method which enables us to trace complex galaxy structures such as rings and faint outer disks. We derive stellar half-mass radii and find that these are on average ~25% smaller than rest-frame g band half-light radii. The average size difference is the same at all redshifts, and does not correlate with stellar mass, specific star formation rate, effective surface density, Sersic index, or galaxy size. Although on average the difference between half-mass size and half-light size is modest, for approximately 10% of massive galaxies this difference is more than a factor two. These extreme galaxies are mostly extended, disk-like systems with large central bulges.