THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES OF MASSIVE STARLESS AND STAR-FORMING CLUMPS

Abstract

ABSTRACT We sort 4683 molecular clouds between 10° &lt; ℓ &lt; 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μ m sources, mid-IR color-selected YSOs, H 2 O and CH 3 OH masers, and UCH ii regions. We also present a combined NH 3 -derived gas kinetic temperature and H 2 O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (&gt;1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial ( α ∼ 0.7) with &gt;75% of clumps with known distance being gravitationally bound ( α &lt; 2). These samples show a statistically significant increase in the median clump mass of Δ M ∼ 170–370 M ⊙ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>˙</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∼</mml:mo> <mml:mn>200</mml:mn> <mml:mo>–</mml:mo> <mml:mn>440</mml:mn> </mml:math> M ⊙ Myr −1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼ M −0.4 . By comparing to the observed number of CH 3 OH maser containing clumps, we estimate the phase lifetime of massive ( M &gt; 10 3 M ⊙ ) starless clumps to be 0.37 ± 0.08 Myr ( M /10 3 M ⊙ ) −1 ; the majority ( M &lt; 450 M ⊙ ) have phase lifetimes longer than their average freefall time.