Radial profiles of lensed z ∼ 1 galaxies on sub-kiloparsec scales

Abstract

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 (Mmol). 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 Mmol 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 Mmol surface density profiles (ΣMmol), 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 ΣMmol, as expected from the Kennicutt-Schmidt law.