Sub-Millimetre Galaxies with Webb: Near-Infrared Counterparts and Multi-wavelength Morphology

Abstract

We utilise the unprecedented depth and resolution of recent early-release science (ERS) JWST observations to define the near-infrared counterparts of sub-millimetre selected galaxies (SMGs). We identify 45 SCUBA-2 SMG positions within The Cosmic Evolution Early Release Science Survey (CEERS) JWST/NIRCam fields. Through an analysis of multi-wavelength $p$-values, NIRCam colours and predicted SCUBA-2 fluxes, we define 43 JWST/NIRCam counterparts to the SCUBA-2 SMGs, finding a 63 per cent agreement with those identified in prior $HST$ studies. Using EaZy-py we fit the available HST and JWST observations to quantify the photometric redshifts of the NIRCam-SMGs, establishing a broad range of redshift from $z$$\approx$0.2$-$5.4 with a median of $z$$\approx$2.29, in agreement with other studies of SMGs. We analyse their rest-frame optical and near-infrared morphological properties (e.g. effective radius (R$_{\rm e}$), S\'ersic index ($n$), CAS, Gini and M$_{20}$), finding, on average, late-type disc-like morphologies with large scatter into the intermediate and merger regions of the non-parametric parameter space. For the non-merging galaxies, we find a median rest-frame optical size and S\'ersic index (and $1\sigma$ scatter) of R$_{\rm e}$=3.10$\pm$1.67kpc and $n$=0.96$\pm$0.66. Whilst in the rest-frame near-infrared we establish more compact, higher S\'ersic index morphologies (R$_{\rm e}$=1.64$\pm$0.97, $n$=1.85$\pm$0.63). We further establish that both the rest-frame optical and near-infrared effective radii correlate negatively (at a 2$\sigma$ level) with redshift whilst the S\'ersic index remains constant with cosmic time. Our results are consistent with the picture of inside-out galaxy evolution, with more centrally concentrated older stellar populations, and more extended, younger star-forming regions whose stellar emission is heavily attenuated in the central regions.