We aim to identify and characterize cores in the high-mass proto-cluster W49, determine their evolutionary stages and measure the associated lifetimes. We built a catalog of 129 cores extracted from an ALMA 1.3mm continuum image at 0.26" (2900au) angular resolution. The association between cores and Hyper/Ultra Compact HII (H/UC HII) regions was established from the analysis of VLA 3.3cm continuum and H30alpha line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29GHz. We identified 40 cores associated with an H/UC HII region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HII region and/or a HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists in prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3cm and not in H30alpha. The spectral indexes from 3.3cm to 1.3mm range from 1, for the youngest cores with partially optically thick free-free emission, to about -0.1, that is optically thin free-free emission obtained for cores likely more evolved. Using as a reference the H/UC HII regions, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6x10^4 yr and 1.4x10^5^yr, respectively. We also showed that HMC can co-exist with H/UC HII regions during a short fraction of the core lifetime, about 2x10^4^yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HII is formed.

Cone search capability for table J/A+A/687/A84/tablea1 (Catalog of cores detected on the 1.3mm continuum image)

Cone search capability for table J/A+A/687/A84/list (List of fits maps)