The structures and total (minor + major) merger histories of massive   galaxies up to z = 3 in the HST GOODS NICMOS Survey: A possible solution to   the size evolution problem
  We investigate the total major (> 1:4 by stellar mass) and minor (> 1:100 by stellar mass) merger history of a population of 80 massive (M_* > 10^11 M_sol) galaxies at high redshifts (z = 1.7 - 3). We utilize extremely deep and high resolution HST H-band imaging from the GOODS NICMOS Survey (GNS), which corresponds to rest-frame optical wavelengths at the redshifts probed. We find that massive galaxies at high redshifts are often morphologically disturbed, with a CAS deduced merger fraction f_m = 0.23 +/- 0.05 at z = 1.7 - 3. We find close accord between close pair methods (within 30 kpc apertures) and CAS methods for deducing major merger fractions at all redshifts. We deduce the total (minor + major) merger history of massive galaxies with M_* > 10^9 M_sol galaxies, and find that this scales roughly linearly with log-stellar-mass and magnitude range. We test our close pair methods by utilizing mock galaxy catalogs from the Millennium Simulation. We compute the total number of mergers to be (4.5 +/- 2.9) / <\tau_m> from z = 3 to the present, to a stellar mass sensitivity threshold of ~ 1:100 (where \tau_m is the merger timescale in Gyr which varies as a function of mass). This corresponds to an average mass increase of (3.4 +/- 2.2) x 10^11 M_sol over the past 11.5 Gyrs due to merging. We show that the size evolution observed for these galaxies may be mostly explained by this merging. 
Asa F. L. Bluck, Christopher J. Conselice, Fernando Buitrago, Ruth   Gruetzbauch, Carlos Hoyos, Alice Mortlock, Amanda E. Bauer
astro-ph.CO