Shape Evolution of Massive Early-Type Galaxies: Confirmation of
  Increased Disk Prevalence at z>1
  We use high-resolution K-band VLT/HAWK-I imaging over 0.25 square degrees to
study the structural evolution of massive early-type galaxies since z~1.
Mass-selected samples, complete down to log(M/M_sun)~10.7 such that `typical'
L* galaxies are included at all redshifts, are drawn from pre-existing
photometric redshift surveys. We then separated the samples into different
redshift slices and classify them as late- or early-type galaxies on the basis
of their specific star-formation rate. Axis-ratio measurements for the ~400
early-type galaxies in the redshift range 0.6<z<1.8 are accurate to 0.1 or
better. The projected axis-ratio distributions are then compared with lower
redshift samples. We find strong evidence for evolution of the population
properties: early-type galaxies at z>1 are, on average, flatter than at z<1 and
the median projected axis ratio at a fixed mass decreases with redshift.
However, we also find that at all epochs z<~2 the very most massive early-type
galaxies (log(M/M_sun)>11.3) are the roundest, with a pronounced lack among
them of galaxies that are flat in projection. Merging is a plausible mechanism
that can explain both results: at all epochs merging is required for early-type
galaxies to grow beyond log(M/M_sun)~11.3, and all early types over time
gradually and partially loose their disk-like characteristics.
