AHubble Space TelescopeNICMOS and ACS morphological study ofz∼ 2 submillimetre galaxies

We present a quantitative morphological analysis using Hubble Space Telescope Near Infrared and Multi-Object SpectrometerH160-band imaging and Advanced Camera for Surveys _(775)-band imaging of 25 spectroscopically confirmed submillimetre galaxies (SMGs) which redshifts between z = 0.7 and 3.4 (z = 2.1). Our analysis also employs a comparison of more typical star-forming galaxies at similar redshifts (such as Lyman-break ) which have lower far-infrared luminosities. This is the first large-scale study of the of SMGs in the near-infrared at ~0.1 arcsec resolution (≾1 kpc). We find that half-light radii of the SMGs (r_h = 2.3 ± 0.3 and 2.8 ± 0.4 kpc in the observed I and H , respectively) and asymmetries are not statistically distinct from the comparison sample star-forming galaxies. However, we demonstrate that the SMG morphologies differ more the rest-frame UV and optical bands than typical star-forming galaxies and interpret as evidence for structured dust obscuration. We show that the composite observed H-band profile of SMGs is better fitted with a high Sersic index (n ~ 2) than with an exponential suggesting the stellar structure of SMGs is best described by a spheroid/elliptical galaxy distribution. We also compare the sizes and stellar masses of SMGs to local and highredshift and find that the SMGs have stellar densities which are comparable to (or slightly larger than) local early-type galaxies and comparable to luminous, red and dense at z ~ 1.5 which have been proposed as direct SMG descendants, although the SMG masses and sizes are systematically larger. Overall, our results suggest that the physical occurring within the galaxies are too complex to be simply characterized by the -frame UV/optical morphologies which appear to be essentially decoupled from all other , such as bolometric luminosity, stellar or dynamical mass.