Structural and morphological properties of ultraluminous infrared
  galaxies at $1<z<3$
  Using the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3)
near-infrared high-resolution imaging from the 3D-HST survey, we analyze the
morphology and structure of 502 ultraluminous infrared galaxies (ULIRGs;
$L_{\rm IR}>10^{12}L_{\odot}$) at $1<z<3$. Their rest-frame optical
morphologies show that high-redshift ULIRGs are a mixture of mergers or
interacting systems, irregular galaxies, disks, and ellipticals. Most of ULIRGs
in our sample can be roughly divided into merging systems and late-type
galaxies (Sb$-$Ir), with relatively high $M_{20}$ ($>-1.7$) and small
S\'{e}rsic index ($n<2.5$), while others are elliptical-like (E/S0/Sa)
morphologies with lower $M_{20}$ ($<-1.7$) and larger $n$ ($>2.5$). The
morphological diversities of ULIRGs suggest that there are different formation
processes for these galaxies. Merger processes between galaxies and disk
instabilities play an important role in the formation and evolution of ULIRGs
at high redshift. In the meantime, we also find that the evolution of the size
($r_{\rm e}$) with redshift of ULIRGs at redshift $z\sim1-3$ follows $r_{\rm
e}\propto(1+z)^{-(0.96\pm0.23)}$.
