2006ApJ...651L.125W

We present a survey of the 6₁₆-5₂₃H₂O maser transition toward a sample of 140 compact cores in infrared dark clouds using the Very Large Array. Strong (>1 Jy) H₂O maser emission was found associated with 17 cores, indicative of star formation in these cores. We infer that the cores with H₂O masers have embedded protostars. Cores associated with maser emission have masses of 12 to 2x10³ M_☉, similar to the mass range in the entire sample. The H₂O maser detection rate (12%) toward the compact, cold cores is much lower than that toward high-mass protostellar objects and ultracompact H II regions. The detection rate of H₂O masers is significantly higher for higher mass cores than for lower mass cores. We suggest that some of the most massive infrared dark cloud cores without H₂O maser emission are at an evolutionary stage earlier than the protostellar phases. They are prime candidates for high-mass starless cores.