  We present stellar mass surface density profiles of a mass-selected sample of
177 galaxies at 0.5 < z < 2.5, obtained using very deep HST optical and
near-infrared data over the GOODS-South field, including recent CANDELS data.
Accurate stellar mass surface density profiles have been measured for the first
time for a complete sample of high-redshift galaxies more massive than 10^10.7
M_sun. The key advantage of this study compared to previous work is that the
surface brightness profiles are deconvolved for PSF smoothing, allowing
accurate measurements of the structure of the galaxies. The surface brightness
profiles account for contributions from complex galaxy structures such as rings
and faint outer disks. Mass profiles are derived using radial rest-frame u-g
color profiles and a well-established empirical relation between these colors
and the stellar mass-to-light ratio. We derive stellar half-mass radii from the
mass profiles, and find that these are on average ~25% smaller than rest-frame
g band half-light radii. This average size difference of 25% 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. These results are robust, but could be impacted if the central
dust extinction becomes high. ALMA observations can be used to explore this
possibility. These results provide added support for galaxy growth scenarios
wherein massive galaxies at these epochs grow by accretion onto their outer
regions.
