2017ApJ...845..108Y

We present the results of a blind millimeter line emitter search using ALMA Band 6 data with a single-frequency tuning toward four gravitational lensing clusters (RXJ1347.5-1145, Abell S0592, MACS J0416.1-2403, and Abell 2744). We construct 3D signal-to-noise ratio (S/N) cubes with 60 and 100 MHz binning, and search for millimeter line emitters. We do not detect any line emitters with a peak S/N > 5, although we do find a line emitter candidate with a peak S/N ≃ 4.5. These results provide upper limits to the CO(3-2), CO(4-3), CO(5-4), and [C II] luminosity functions at z ≃ 0.3, 0.7, 1.2, and 6, respectively. Because of the magnification effect of gravitational lensing clusters, the new data provide the first constraints on the CO and [C II] luminosity functions at unprecedentedly low luminosity levels, i.e., down to <=10^–3 - 10^–1 Mpc^–3 dex^–1 at L_CO^′^∼10⁸–10¹⁰ K km s^–1 pc² and <=10^–3-10^–2 Mpc^–3 dex^–1 at L_[CII]∼10⁸–10¹⁰ L_☉, respectively. Although the constraints to date are not yet stringent, we find that the evolution of the CO and [C II] luminosity functions are broadly consistent with the predictions of semi-analytical models. This study demonstrates that the wide observations with a single-frequency tuning toward gravitational lensing clusters are promising for constraining the CO and [C II] luminosity functions.