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 (NOEMA) 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 $\hat{I}¼\approx 7-22$ with a luminosity-weighted mean $⟨\hat{I}¼⟩\approx 13$. 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 $L_{\mathrm{CO}(3-2)}^{\prime }=(5.53\pm 0.69)\times 10^{10}\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\mathrm{p}{\mathrm{c}}^2$, a cold gas mass $M_{\mathrm{gas}}=(3.86\pm 0.33)\times 10^{10}{M}_{\odot }$, a dynamical mass $M_{\mathrm{dyn}}{\sin }^{2}i=3.9_{-1.5}^{+1.8}\times 10^{10}{M}_{\odot }$, and a gas mass fraction $f_{\mathrm{gas}}{\csc }^{2}i=1.0_{-0.4}^{+0.8}$. The line brightness temperature ratio of $r_{3,1}\approx 1.6$ 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.

8 pages, 5 figures, accepted to ApJ