Colloq Abstract -Shirley

by Hubertus Intema last modified Feb 28, 2017 by Lori Appel

March 10

11am Mountain

Yancy Shirley (UA)

The Physical Properties of Massive Dense Clumps in Different Evolutionary Stages in the Milky Way


Galactic Plane Surveys at Far-Infrared through Millimeter wavelengths have provided the most unbiased maps of dust continuum emission in the Milky Way.   The Bolocam Galactic Plane Survey catalogued 10^4 dense clumps of a gas and dust - current and future sites of star formation within the Galaxy.  Followup molecular line observations of several thousand clumps in lines of NH3 and HCO+ with the GBT and SMT determine the thermal and turbulent state of the clumps.  The BGPS team has developed a Bayesian technique for constraining the heliocentric distance to the clumps and use Monte Carlo sampling of the posterior distance distributions to more properly account for uncertainties in calculations of the physical variable (i.e. size, mass, luminosity, etc.).  Clumps have been sorted into evolutionary categories by comparing the 1.1mm continuum with near/mid/far-infrared surveys, masers surveys, and radio continuum (VLA) surveys.  The distributions of flux density, flux concentration, kinetic temperature, mass surface density, radius, and mass all show strong progressions when sorted by star formation indicators with increasing luminosity.  A population of over 2000 starless clump candidates have been identified which have no evidence from Galactic plane survey observations for star formation.  The lifetime of the starless clump phase is found to be a function of the mass of the clumps (t ~ 1/M) with the majority of clumps having starless phase lifetimes longer than their average free-fall times.  However, bew followup observations of the most massive starless clump candidates with ALMA  indicate that current Galactic plane surveys from near-infrared through centimeter wavelengths are not sensitive enough to detect low-mass star formation within clumps at distances of a few kpc.  Initial analysis of the ALMA observations probe fragmentation down to the core scales and are consistent with thermal Jean fragmentation in these massive clumps.