Detection of a Substantial Molecular Gas Reservoir in a Brightest Cluster Galaxy at z = 1.7

We report the detection of CO(2-1) emission coincident with the brightest cluster galaxy (BCG) of the high-redshift galaxy cluster SpARCS1049+56, with the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT). We confirm a spectroscopic redshift for the gas of z = 1.7091 0.0004, which is consistent with the systemic redshift of the cluster galaxies of z = 1.709. The line is well fit by a single-component Gaussian with an RSR-resolution-corrected FWHM of 569 63 km s−1. We see no evidence for multiple velocity components in the gas, as might be expected from the multiple image components seen in near-infrared imaging with the Hubble Space Telescope. We measure the integrated flux of the line to be 3.6 0.3 Jy km s−1, and using = 0.8 M (K km s−1 pc2)−1, we estimate a total molecular gas mass of 1.1 0.1 × 1011 M and a MH2/M ∼ 0.4. This is the largest gas reservoir detected in a BCG above z > 1 to date. Given the infrared-estimated star formation rate of 860 130 M yr−1, this corresponds to a gas depletion timescale of ∼0.1 Gyr. We discuss several possible mechanisms for depositing such a large gas reservoir to the cluster center-e.g., a cooling flow, a major galaxy-galaxy merger, or the stripping of gas from several galaxies-but conclude that these LMT data are not sufficient to differentiate between them.