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SUMMARY:Magnetic fields and the Galactic star formation rate - Dr. Sven Va
 n Loo (University of Leeds)
DTSTART:20150223T160000Z
DTEND:20150223T170000Z
UID:TALK56074@talks.cam.ac.uk
CONTACT:Adrian Barker
DESCRIPTION:Star formation occurs primarily in giant molecular clouds (GMC
 s)\, but at a very slow and inefficient rate\, usually being restricted to
  a small fraction of the cloud volume\, where stars form in localized clus
 ters. This suggests that the rate limiting step controlling star formation
  in galactic systems is the formation of dense gas clumps in GMCs.  We pre
 sent numerical hydrodynamic and magnetohydrodynamic simulations \nof the e
 volution of GMCs inside a kiloparsec-scale patch of a galactic disc with a
  minimum resolution of ~0.5 parsec. The thermal behaviour of the gas is fo
 llowed using extinction-dependent heating and cooling functions.\n\nThe hy
 drodynamical simulations show that energy from galactic shear and large-sc
 ale cloud motions continuously cascades down to and within GMCs. This ener
 gy drives the turbulent motions within the clouds to balance gravitational
  collapse. The virial parameters of the clouds remain above unity for time
 s-scales exceeding the free-fall time of GMCs. When we implement star form
 ation ar a slow\, inefficient rate of 2% of the local free-fall time\, the
  star formation rates within the patch are about 2 orders of magnitude lar
 ger than the observed Kennicutt-Schmidt relation due to over-production of
  dense gas clumps. We expect magnetic support is required to inhibit dense
  core formation.\n\nTo investigate this hypothesis we carry-out MHD simula
 tions\, using realistic field strengths\, of the same kiloparsec-scale reg
 ion. These runs indeed show that a magnetic field inhibits dense clump for
 mation to a fraction of the rate derived from the non-magnetic models. Det
 ailed comparison of the results of these simulations with observed GMCs an
 d IRDCs allow us to elucidate the dominant physics processes controlling s
 tar formation in galactic disks.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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