689 research outputs found
Stellar Populations in Ten Clump-Cluster Galaxies of the Ultra Deep Field
Color-color diagrams for the clump and interclump emission in 10
clump-cluster galaxies of the Ultra Deep Field are made from B,V,i, and z
images and compared with models to determine redshifts, star formation
histories, and galaxy masses. The clump colors suggest declining star formation
over the last ~0.3 Gy, while the interclump emission is older. The clump
luminous masses are typically 6x10^8 Msun and their diameters average 1.8 kpc.
Total galaxy luminous masses average 6.5x10^10 Msun. The distribution of axial
ratios is consistent with a thick disk geometry. The ages of the clumps are
longer than their internal dynamical times by a factor of ~8, so they are
stable clusters, but the clump densities are only ~10 times the limiting tidal
densities, so they could be deformed by tidal forces. This is consistent with
the observation that some clumps have tails. The clumps could form by
gravitational instabilities in accreting disk gas, or they could be captured as
gas-rich dwarf galaxies. Support for this second possibility comes from the
high abundance of nearly identical bare clumps in the UDF field. Several
clump-clusters have disk densities that are much larger than in local disks,
suggesting they do not survive but get converted into ellipticals by
collisions.Comment: 34 pgs, including 12 figures, accepted by Astrophysical Journal for
20 July 2005 v.62
Formation of massive clouds and dwarf galaxies during tidal encounters
Gerola et al. (1983) propose that isolated dwarf galaxies can form during galaxy interactions. As evidence of this process, Mirabel et al. (1991) find 10(exp 9) solar mass clouds and star formation complexes at the outer ends of the tidal arms in the Antennae and Superantennae galaxies. We describe observations of HI clouds with mass greater than 10(exp 8) solar mass in the interacting galaxy pair IC 2163/NGC 2207. This pair is important because we believe it represents an early stage in the formation of giant clouds during an encounter. We use a gravitational instability model to explain why the observed clouds are so massive and discuss a two-dimensional N-body simulation of an encounter that produces giant clouds
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