Blind Millimeter Line Emitter Search using ALMA Data Toward Gravitational Lensing Clusters

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 similar or equal to 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 similar or equal to 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 less than or similar to 10(-3)-10(-1) Mpc(-3) dex(-1) at L'(CO) similar to 10(8)-10(10) Kkms(-1) pc(2) and less than or similar to 10(-3)-10(-2) Mpc(-3) dex(-1) at L[C II] similar to 10(8)-10(10) L-circle dot, 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.