Radial profiles of lensed $z \sim 1$ 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 H 2 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 to 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.

Multiply lensed star forming clumps in the A521-sys1 galaxy at redshift 1

“…ci_4). In particular, we observe two massive clumps close to the centre of the galaxy, namely ci_1 and ci_8 (the latter sitting at the coordinates of the bulge, Nagy et al 2021); their young ages (4 and 20 Myr, respectively) suggest that star formation is taking place also at the centre of the galaxy. At the same time, the large mass, log(M/M ) = 8.3, and density, ΣM > 10 3 M pc −2 of clump ci_8, may suggest that we are looking at the formation of a proto-bulge.…”

“…ALMA observations of A521-sys1 were acquired during Cycle 4 (ID: 2016.1.00643.S) in band 6, targeting the CO(4-3) emission line, and were presented in Girard et al (2019) and in Nagy et al (2021), along with their data reduction analysis. The high resolution of the ALMA observations (beam size: 0.19 × 0.16 ) allows the study of molecular gas on the same scales as the stellar content; the study of the individual giant molecular clouds (GMCs) is presented in Dessauges-Zavadsky et al (2022).…”

“…In addition, both the molecular gas mass surface density, Σ(M mol ), and the SFR surface density, Σ(SFR), are elevated by a factor of ∼ 10 compared to local MS galaxies, as expected for high-z gas-rich galaxies. The radial profiles of Σ(M mol ) and Σ(SFR) are very shallow (Nagy et al 2021), suggesting an intense star-formation activity throughout the entire galaxy, as also indicated by the presence of UV clumps in var- ious sub-regions of A521-sys1. The gravitational lensing produced by the foreground cluster allows the analysis of A521-sys1 clumps down to scales of few tens of parsecs.…”

“…In the context of analyses of clumps on small physical scales, we here present the study of the strongly lensed arc at z = 1.04 in Abell 0521 (A521); following the nomenclature in Patrício et al (2018) we will refer to the galaxy as A521-sys1 in the rest of the paper. With a stellar mass of M * = (7.4 ± 1.2) × 10 10 M and a SFR of (26 ± 5) M yr −1 (Nagy et al 2021), A521-sys1 can be considered a typical main-sequence star-forming galaxy at z ∼ 1 (e.g. Speagle et al 2014).…”

Possible Ongoing Merger Discovered by Photometry and Spectroscopy in the Field of the Galaxy Cluster PLCK G165.7+67.0

“…Starting at first by incorporating the constraints from one image multiplicity to anchor the lens model (Franx et al 1997;Frye & Broadhurst 1998), to increasing that number up to dozens of image multiplicities (Kneib et al 2004;Broadhurst et al 2005), the modeling schemes grew over time into a precision science (e. g., Jullo et al 2007;Zitrin et al 2009Zitrin et al , 2015Kneib & Natarajan 2011). Lens models can flag the high magnification sightlines, offering windows into the distant universe at z > ∼ 10 (e. g., Coe et al 2013), as well as rare studies of the interstellar medium within lensed sources at z > ∼ 1 (e. g., Frye et al 2012;Sharma et al 2018;Fujimoto et al 2021;Nagy et al 2021). Knowing the exact placement of the critical curve enables searches at close angular separations ( < ∼ 2 ), resulting in detections of compact sources with ultra-high magnification factors of several thousands (Miralda-Escude 1991;Venumadhav et al 2017;Diego et al 2018;Oguri et al 2018;Windhorst et al 2018;Dai et al 2018Dai & Miralda-Escudé 2020;Vanzella et al 2020), and yielding the discovery of individual stars at cosmological distances known as caustic transients (Kelly et al 2018;Kaurov et al 2019;Chen et al 2019;Welch et al 2022).…”