The cold interstellar medium of a normal sub-<i>L</i>* galaxy at the end of reionization
No Thumbnail Available
Date
2024
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
We present the results of a similar to 60-h multiband observational campaign with the Atacama Large Millimeter Array targeting a spectroscopically confirmed and lensed sub-L* galaxy at z = 6.07, first identified during the ALMA Lensing Cluster Survey (ALCS). We sampled the dust continuum emission from rest frame 90-370 mu m at six different frequencies and set constraining upper limits on the molecular gas line emission and content by targeting the CO (7 - 6) and [C I](P-3(2)-P-3(1)) transitions in two lensed images with mu greater than or similar to 20. Complementing these submillimeter observations with deep optical and near-IR photometry and spectroscopy with JWST, we find this galaxy to form stars at a rate of SFR similar to 7 M-circle dot yr(-1), similar to 50 - 70% of which is obscured by dust. This is consistent with what one would predict for a M-* similar to 7.5 x 10(8) M-circle dot object by extrapolating the relation between the fraction of the obscured star formation rate and stellar mass at z < 2.5 and with observations of IR-detected objects at 5 < z < 7. The light-weighted dust temperature of T-dust similar to 50 K is similar to that of more massive galaxies at similar redshifts, although with large uncertainties and with possible negative gradients. We measure a dust mass of M-dust similar to 1.5 x 10(6) M-circle dot and, by combining [C I], [C II], and a dynamical estimate, a gas mass of M-gas similar to 2 x 10(9) M-circle dot. Their ratio (delta(DGR)) is in good agreement with predictions from models and empirical relations in the literature. The dust-to-stellar mass fraction of f(dust) similar to 0.002 and the young stellar age (100 - 200 Myr) are consistent with efficient dust production via supernovae, as predicted by existing models and simulations of dust evolution. Also, the expected number density of galaxies with M-dust similar to 10(6) M-circle dot at z = 6 from a subset of these models is in agreement with the observational estimate that we set from the parent ALCS survey. The combination of gravitational lensing and deep multiwavelength observations allowed us to probe luminosity and mass regimes up to two orders of magnitude lower than what has been explored so far for field galaxies at similar redshifts. Our results serve as a benchmark for future observational endeavors of the high-redshift and faint sub-L* galaxy population that might have driven the reionization of the Universe.
Description
Keywords
gravitational lensing: strong, galaxies: evolution, galaxies: formation, galaxies: high-redshift, galaxies: ISM, galaxies: star formation