The Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star Forming Clumps

• Main Authors: Svoboda, Brian E, Shirley, Yancy L, Battersby, Cara, Rosolowsky, Erik W, Ginsburg, Adam G, Ellsworth-Bowers, Timothy P, Pestalozzi, Michele R, Dunham, Miranda K, EvansII, Neal J, Bally, John, Glenn, Jason
• Format: Journal Article
• Language: English
• Published: 27-11-2015
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.1511.08810

We sort $4683$ molecular clouds between $10^\circ< \ell <65^\circ$ from the
Bolocam Galactic Plane Survey based on observational diagnostics of star
formation activity: compact $70$ $\mu{\rm m}$ sources, mid-IR color-selected
YSOs, ${\rm H_2O}$ and ${\rm CH_3OH}$ masers, and UCHII regions. We also
present a combined ${\rm NH_3}$-derived gas kinetic temperature and ${\rm
H_2O}$ maser catalog for $1788$ clumps from our own GBT 100m observations and
from the literature. We identify a subsample of $2223$ ($47.5\%$) starless
clump candidates, 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 ($>1$ dex)
progressions when sorted by star formation indicator. The median starless clump
candidate is marginally sub-virial ($\alpha \sim 0.7$) with $>75\%$ of clumps
with known distance being gravitationally bound ($\alpha < 2$). These samples
show a statistically significant increase in the median clump mass of $\Delta M
\sim 170-370$ M$_\odot$ from the starless candidates to clumps associated with
protostars. This trend could be due to (i) mass growth of the clumps at
$\dot{M}\sim200-440$ Msun Myr$^{-1}$ for an average free-fall $0.8$ Myr
time-scale, (ii) a systematic factor of two increase in dust opacity from
starless to protostellar phases, (iii) and/or a variation in the ratio of
starless to protostellar clump lifetime that scales as $\sim M^{-0.4}$. By
comparing to the observed number of ${\rm CH_3OH}$ maser containing clumps we
estimate the phase-lifetime of massive ($M>10^3$ M$_\odot$) starless clumps to
be $0.37 \pm 0.08 \ {\rm Myr} \ (M/10^3 \ {\rm M}_\odot)^{-1}$; the majority
($M<450$ M$_\odot$) have phase-lifetimes longer than their average free-fall
time.