2022A&A...657A..25N

We study the spatially resolved physical properties of the Cosmic Snake arc in MACS J1206.2-0847 and the arc in Abell 0521 (A521). These are two strongly lensed galaxies at redshifts z = 1.036 and z = 1.044. We used observations of the Hubble Space Telescope (HST) and the Atacama Large Millimeter/submillimeter Array (ALMA). The former gives access to the star formation rate (SFR) and stellar mass (M_*), and the latter to the H₂ molecular gas mass (M_mol). HST and ALMA observations have similar angular resolutions of 0.15'' - 0.2'', which with the help of strong gravitational lensing enable us to reach spatial resolutions down to ∼30 pc and ∼100 pc in these two galaxies, respectively. These resolutions are close to the resolution of observations of nearby galaxies. We study the radial profiles of SFR, M_*, and M_mol surface densities of these high-redshift galaxies and compare the corresponding exponential scale lengths with those of local galaxies. We find that the scale lengths in the Cosmic Snake are about 0.5 kpc - 1.5 kpc, and they are 3-10 times larger in A521. This is a significant difference knowing that the two galaxies have comparable integrated properties. These high-redshift scale lengths are nevertheless comparable to those of local galaxies, which cover a wide distribution. The particularity of our high-redshift radial profiles is the normalisation of the M_mol surface density profiles (ΣM_mol), which are offset by up to a factor of 20 with respect to the profiles of z = 0 counterparts. The SFR surface density profiles are also offset by the same factor as ΣM_mol, as expected from the Kennicutt-Schmidt law.