Detection of Prominent Stellar Disks in the Progenitors of Present-day
  Massive Elliptical Galaxies
  Massive galaxies at higher redshifts ($\emph{z}$ $>$ 2) show different
characteristics from their local counterparts: They are compact and most likely
have a disk. In this study, we trace the evolution of local massive galaxies by
performing a detailed morphological analysis, namely, fitting single S\'{e}rsic
profiles and performing bulge+disk decompositions. We analyze $\sim$ 250
massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS,
GOODS-South and GOODS-North). We confirm that both star-forming and quiescent
galaxies increase their sizes significantly from $\emph{z}$ $\approx$ 2.5 to
the present day. The global S\'{e}rsic index of quiescent galaxies increases
over time (from $n$ $\approx$ 2.5 to $n$ $>$ 4), while that of star-forming
galaxies remains roughly constant ($n$ $\approx$ 2.5). By decomposing galaxy
profiles into bulge+disk components, we find that massive galaxies at high
redshift have prominent stellar disks, which are also evident from visual
inspection of the images. By $z$ $\approx$ 0.5, the majority of the disks
disappear and massive quiescent galaxies begin to resemble the local elliptical
galaxies. Star-forming galaxies have lower bulge-to-total ratios ($B/T$) than
their quiescent counterparts at each redshift bin. The bulges of star-forming
and quiescent galaxies follow different evolutionary histories, while their
disks evolve similarly. We conclude that major mergers, along with minor
mergers, have played a crucial role in the significant size increase of
high-\emph{z} galaxies and the destruction of their massive and large-scale
disks.
