Water Masers Associated with Infrared Dark Cloud Cores

We present a survey of the 6 16 -5 23 H 2 O maser transition toward a sample of 140 compact cores in infrared dark clouds using the Very Large Array. Strong (>1 Jy) H 2 O maser emission was found associated with 17 cores, indicative of star formation in these cores. We infer that the cores with H 2 O masers have embedded protostars. Cores associated with maser emission have masses of 12 to 2 × 10 3 M ☉ , similar to the mass range in the entire sample. The H 2 O 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 H 2 O 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 H 2 O maser emission are at an evolutionary stage earlier than the protostellar phases. They are prime candidates for high-mass starless cores.