Stellar Populations in 10 Clump‐Cluster Galaxies of the Hubble Ultra Deep Field

Color-color diagrams for the clump and interclump emission in 10clump-cluster galaxies of the Ultra Deep Field are made from B,V,i, and zimages and compared with models to determine redshifts, star formationhistories, and galaxy masses. The clump colors suggest declining star formationover the last ~0.3 Gy, while the interclump emission is older. The clumpluminous 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 axialratios is consistent with a thick disk geometry. The ages of the clumps arelonger than their internal dynamical times by a factor of ~8, so they arestable clusters, but the clump densities are only ~10 times the limiting tidaldensities, so they could be deformed by tidal forces. This is consistent withthe observation that some clumps have tails. The clumps could form bygravitational instabilities in accreting disk gas, or they could be captured asgas-rich dwarf galaxies. Support for this second possibility comes from thehigh abundance of nearly identical bare clumps in the UDF field. Severalclump-clusters have disk densities that are much larger than in local disks,suggesting they do not survive but get converted into ellipticals bycollisions.Comment: 34 pgs, including 12 figures, accepted by Astrophysical Journal for 20 July 2005 v.62