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

¹ Observatoire de Genève, Université de Genève, Versoix, Switzerland
e-mail: david.nagy@unige.ch
² Université Lyon, Université Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Saint-Genis-Laval, France
³ LERMA, Observatoire de Paris, PSL Research Université, CNRS, Sorbonne Université, UPMC, Paris, France
⁴ Department of Astronomy, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden
⁵ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712, USA

Received: 15 June 2021
Accepted: 20 August 2021

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 (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.