2,988 research outputs found
Fire from Ice - Massive Star Birth from Infrared Dark Clouds
I review massive star formation in our Galaxy, focusing on initial conditions
in Infrared Dark Clouds (IRDCs), including the search for massive pre-stellar
cores (PSCs), and modeling of later stages of massive protostars, i.e., hot
molecular cores (HMCs). I highlight how developments in astrochemistry, coupled
with rapidly improving theoretical/computational and observational capabilities
are helping to improve our understanding of the complex process of massive star
formation.Comment: To appear in proceedings of IAU Symp. 322, Astrochemistry VII Through
the Cosmos from Galaxies to Planet
Clustered Massive Star Formation in Molecular Clouds
I review some important questions in the field of massive star formation:
What are the initial conditions for proto star clusters and how do they arise?
What are the initial conditions for individual massive star formation within
star clusters? How do massive protostars accumulate their mass? I compare the
Turbulent Core Model (McKee & Tan 2003) to several nearby regions, including
Orion KL. Here I also discuss the origin of BN's high proper motion.Comment: 10 pages, 2 figures, invited review, to appear in "Massive Star Birth
- A Crossroads of Astrophysics" (CUP), eds. R. Cesaroni, E. Churchwell, M.
Felli, and C. M. Walmsle
High-dynamic-range extinction mapping of infrared dark clouds: Dependence of density variance with sonic Mach number in molecular clouds
Measuring the mass distribution of infrared dark clouds (IRDCs) over the wide
dynamic range of their column densities is a fundamental obstacle in
determining the initial conditions of high-mass star formation and star cluster
formation. We present a new technique to derive high-dynamic-range,
arcsecond-scale resolution column density data for IRDCs and demonstrate the
potential of such data in measuring the density variance - sonic Mach number
relation in molecular clouds. We combine near-infrared data from the
UKIDSS/Galactic Plane Survey with mid-infrared data from the Spitzer/GLIMPSE
survey to derive dust extinction maps for a sample of ten IRDCs. We then
examine the linewidths of the IRDCs using 13CO line emission data from the
FCRAO/Galactic Ring Survey and derive a column density - sonic Mach number
relation for them. For comparison, we also examine the relation in a sample of
nearby molecular clouds. The presented column density mapping technique
provides a very capable, temperature independent tool for mapping IRDCs over
the column density range equivalent to A_V=1-100 mag at a resolution of 2".
Using the data provided by the technique, we present the first direct
measurement of the relationship between the column density dispersion,
\sigma_{N/}, and sonic Mach number, M_s, in molecular clouds. We detect
correlation between the variables with about 3-sigma confidence. We derive the
relation \sigma_{N/} = (0.047 \pm 0.016) Ms, which is suggestive of the
correlation coefficient between the volume density and sonic Mach number,
\sigma_{\rho/} = (0.20^{+0.37}_{-0.22}) Ms, in which the quoted
uncertainties indicate the 3-sigma range. When coupled with the results of
recent numerical works, the existence of the correlation supports the picture
of weak correlation between the magnetic field strength and density in
molecular clouds (i.e., B ~ \rho^{0.5}).Comment: Accepted for publication in A&A. 29 pages. Download the version with
full-resolution figures from
http://www.mpia-hd.mpg.de/homes/jtkainul/NexusI/PaperII_arxiv.pdf.g
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