HOBYS: 46 MDCs found in NGC 6334

A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75M_{sun}_ for MDCs in NGC 6334. MDCs have temperatures of 9.5-40K, masses of 75-1000M_{sun}_, and densities of 1x10^5^-7x10^7^cm^-3^. Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70{mu}m emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates.

The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7x10^4^yr and at most 3x10^5^yr respectively, suggest a dynamical scenario of high-mass star formation.

The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC 6334, favoring a scenario presented here, which simultaneously forms clouds, ridges, MDCs, and high-mass protostars.