Surveying dense gas with bolocam: There are no pre-stellar massive clusters in the first quadrant

Abstract

We search the λ = D 1:1mm Bolocam Galactic Plane Survey for clumps containing sufficient mass to form ~104M๏ star clusters. Eighteen candidate massive proto-clusters are identified in the first Galactic quadrant outside of the central kiloparsec. This sample is complete to clumps with mass Mclump> 104M๏ and radius r ≤ 2.5 pc. The overall Galactic massive cluster formation rate is CFR(Mcluster> 104) ≤ 5 Myr-1. We find that all massive proto-clusters in the first quadrant are actively forming massive stars and place an upper limit of τstarless< 0:5Myr on the lifetime of the starless phase of massive cluster formation and a strong upper limit on the ratio of the starless timescale to the ‘dust-rich’ timescale τstarless/τclump< 0.25. Our results hint that massive stars form early in massive proto-clusters.