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JOINT DAUT-ICTP-OATS-SISSA COLLOQUIUM
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Speaker:
Bruce Elmegreen (IBM Watson Research Center, Yorktown)
Title:
Star formation in High Redshift Galaxies
Date: Thursday, September 20th, 2007
Time: 16:00
Venue: Villa Bazzoni
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Abstract:
The Hubble Space Telescope for optical and near-infrared light and the
Spitzer Space Telescope for the infrared have opened up a view of star
formation in young galaxies that has never been possible
before. Because the most distant galaxies are viewed as they were when
light left them long ago, we can see the various steps of galaxy
formation throughout time. Our work in the last three years has
concentrated on the nature of star formation in these galaxies, many
of which are quite peculiar by the standards of our own
neighborhood. The dominant peculiarity is the presence of enormous
young clusters and star complexes in the disk systems. These complexes
are 1000 times more massive than any star forming regions in galaxies
today, and yet they appear to form by standard processes, which begin
with a localized collapse of disk gas. The galaxy disks are also
smaller and thicker than today's spiral galaxies, and many have less
than 1/10 the mass of the Milky Way. This combination of small
galaxies and big star complexes makes the youngest disks look very
patchy, yet, remarkably, the average positions of these patches, if
they were to be smoothed out in each disk, has the same radial density
profile as that observed in the more normal spiral galaxies that are
also in deep fields. The thicknesses of the star complexes are also
about equal to the galaxy thicknesses. Thus it appears that spiral
galaxy disks form by the dispersal and dissolution of giant star
complexes, which form by gravitational instabilities in thick and
turbulent gas layers. This process seems to accompany the growth of
galaxy disks over cosmic time, indicating that the growth occurs
primarily by the accretion of gas for systems that end up as
spirals. Clumpy disk star formation also precedes the formation of
spirals and ellipticals, going back to the bandshifting limit of the
ACS camera on HST, which is z~5. Thus most star formation in the
Universe begins in disk systems, and from these, all of today's Hubble
types eventually form.
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