The SCUBA-2 Cosmology Legacy Survey: The EGS deep field – II. Morphological transformation and multiwavelength properties of faint submillimetre galaxies

We present a multi-wavelength analysis of galaxies selected at 450 and 850 m from the deepest SCUBA-2 observations in the Extended Groth Strip (EGS) field, which have an average depth of 450 = 1.9and 850 = 0.46 mJy beam -1 over 70 arcmin 2 . The final sample comprises 95 sources: 56 (59 %) are detected at both wavelengths, 31 (33 %) are detected only at 850 m, and 8 (8 %) are detected only at 450 m. We identify counterparts for 75 % of the whole sample. The redshift distributions of the 450 and 850 m samples peak at different redshifts with median values of z = 1.66 0.18 and z = 2.300.20, respectively. However, the two populations have similar IR luminosities, SFRs, and stellar masses, with mean values of 1.5 0.2 10 12 L , 150 20 M /yr, and 9.0 0.6 10 10 M , respectively. This places most of our sources ( 85 %) on the high-mass end of the 'main-sequence' of star-forming galaxies. Exploring the IR excess vs UV-slope (IRX-) relation we find that the most luminous galaxies are consistent with the Meurer law, while the less luminous galaxies lie below this relation. Using the results of a two-dimensional modelling of the HST H 160 -band imaging, we derive a median Srsic index of n = 1.4 +0.3 -0.1 and a median half-light radius of r 1/2 = 4.8 0.4 kpc. Based on a visual-like classification in the same band, we find that the dominant component for most of the galaxies at all redshifts is a disk-like structure, although there is a transition from irregular disks to disks with a spheroidal component at z 1.4, which morphologically supports the scenario of SMGs as progenitors of massive elliptical galaxies.