2015ApJ...805...72M

We present new observations of the quiescent giant molecular cloud GCM0.253+0.016 in the Galactic center, using the upgraded Karl G. Jansky Very Large Array. Observations were made at wavelengths near 1 cm, at the K (24-26 GHz) and Ka (27 and 36 GHz) bands, with velocity resolutions of 1-3 km/s and spatial resolutions of ∼0.1 pc, at the assumed 8.4 kpc distance of this cloud. The continuum observations of this cloud are the most sensitive yet made, and reveal previously undetected emission which we attribute primarily to free-free emission from external ionization of the cloud. In addition to the sensitive continuum map, we produce maps of 12 molecular lines: 8 transitions of NH₃-(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), and (9, 9), as well as the HC₃ N (3-2) and (4-3) lines, and CH₃OH 4_–1-3₀, the latter of which is known to be a collisionally excited maser. We identify 148 CH₃OH 4_–1-3₀(36.2 GHz) sources, of which 68 have brightness temperatures in excess of the highest temperature measured for this cloud (400 K) and can be confirmed to be masers. The majority of these masers are concentrated in the southernmost part of the cloud. We find that neither these masers nor the continuum emission in this cloud provide strong evidence for ongoing star formation in excess of that previously inferred by the presence of an H₂ O maser.