The Atacama Cosmology Telescope: CO(J = 3 – 2) Mapping and Lens Modeling of an ACT-selected Dusty Star-forming Galaxy

Abstract

We report Northern Extended Millimeter Array CO( J  = 3 − 2) observations of the dusty star-forming galaxy ACT-S J020941+001557 at z  = 2.5528, which was detected as an unresolved source in the Atacama Cosmology Telescope (ACT) equatorial survey. Our spatially resolved spectral line data support the derivation of a gravitational lens model from 37 independent velocity channel maps using a pixel-based algorithm, from which we infer a velocity-dependent magnification factor μ  ≈ 7–22 with a luminosity-weighted mean . The resulting source-plane reconstruction is consistent with a rotating disk, although other scenarios cannot be ruled out by our data. After correction for lensing, we derive a line luminosity , a cold gas mass , a dynamical mass , and a gas mass fraction . The line brightness temperature ratio of r 3,1  ≈ 1.6 relative to a Green Bank Telescope CO( J  = 1 − 0) detection may be elevated by a combination of external heating of molecular clouds, differential lensing, and/or pointing errors.