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

We present a multiwavelength analysis of galaxies selected at 450 and 850 μmfrom the deepest SCUBA-2 observations in the Extended Groth Strip (EGS) field, which have an average depth of σ₄₅₀ = 1.9 and σ₈₅₀ = 0.46 mJy beam^-1 over ~70 arcmin². The final sample comprises 95 sources: 56 (59 per cent) are detected at both wavelengths, 31 (33 per cent) are detected only at 850 μm, and 8 (8 per cent) are detected only at 450 μm.We identify counterparts for 75 per cent of the whole sample. The redshift distributions of the 450 and 850 μmsamples peak at different redshifts with median values of z = 1.66 ± 0.18 and z = 2.30 ± 0.20, respectively. However, the two populations have similar IR luminosities, SFRs, and stellar masses, with mean values of 1.5 ± 0.2 × 10¹² L_⊙, 150 ± 20M_⊙ yr^-1, and 9.0 ± 0.6 × 10¹⁰M_⊙, respectively. This places most of our sources (≳85 per cent) on the high-mass end of the main sequence of starforming galaxies. Exploring the IR excess versus UV-slope (IRX-β) 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 H₁₆₀-band imaging, we derive a median Sérsic index of n = 1.4_-0.1 ^+0.3 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 disc-like structure, although there is a transition from irregular discs to discs with a spheroidal component at z ~ 1.4, which morphologically supports the scenario of SMGs as progenitors of massive elliptical galaxies.