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Wednesday 06 Jul 2016Temperatures and Distances to High-mass Star-forming Regions in the Inner Galaxy

Marion Wienen -

Physics, 4th Floor 14:00-14:40

The initial conditions of molecular clumps, in which high-mass stars
form, are still largely unknown. In particular, progress has to be made
in the investigation of the phases before ultracompact HII regions have
formed and the newly formed high-mass (proto) stars emerge in the
infrared. These phases are best searched for and detected by
(sub)millimeter dust continuum and high-density molecular tracers.
ATLASGAL, the first unbiased continuum survey of the whole inner
Galactic plane at 870 micron, has therefore been carried out to provide
a global view of cold dust and star formation at submillimeter
wavelengths. Although the earliest phases of high-mass star formation
can be identified by the dust continuum, directly probing the material
from which the stars form, there is still a lack of physical properties
such as temperature, density and velocity information. We therefore
followed up a large sample of ATLASGAL sources in the (1,1) to (3,3)
inversion transitions of the high-density tracer ammonia, which is an
excellent probe of high-mass clumps with low temperatures. The
rotational temperatures and linewidths derived from the ammonia
observations are compared with the observationally defined evolutionary
sequence suggested for massive star formation.
The determination of important properties such as masses and sizes
requires the derivation of distances using the measured ammonia
velocities. A large number of complexes consisting of ATLASGAL sources
is identified based on spatial and kinematic information. From their
radial velocities and a rotation curve model we have determined
distances. For complexes found within the solar circle there are two
possible distances and we used HI data to resolve these ambiguities.
With the derived distances we have estimated the clump masses and sizes
and evaluated their stability via their virial mass. In addition, we
have found a correlation between the number of ATLASGAL sources as a
function of galactocentric radius and the position of the spiral arms
revealing a link between them.

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