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C. Papovich (JHU), M. Dickinson, H.C. Ferguson (STScI)
Using a new photometric catalog based on HST NICMOS, WFPC2, and ground--based Ks-band imaging of the Hubble Deep Field North, we compare the spectral energy distributions (SEDs) of a sample of Lyman--Break Galaxies (LBGs) at 2.0 < z < 3.5 to synthetic simple stellar population models. The LBGs SEDs are broadly similar to local starburst--galaxy analogs with modest amounts of reddening. Individual galaxies are typically well fit by models with population ages of a few Myr to a few Gyr, with a median age of 60-100 Myr (modulo IMF and metallicity), and mean dust extinctions of 1-2 mag at 1700 Å. Although constraints on the galaxies' ages, extinction, metallicity, IMF, and prior star--formation history are generally weak, we find good constraints on the LBG total stellar masses. The best fitting models typically correspond to LBG stellar masses below that of a present--day L* galaxy, with typical values of one--tenth L*. We tracked the evolution these galaxies to the present--day by allowing the best--fit star--formation histories to continue to z=0. These models generally favor present--day stellar masses that remain sub--L*. If these models are correct, then LBGs require further accretion or merging to end up as L*--sized galaxies today. However, there are allowable models that produce present--day stellar masses comparable to (and even exceeding) the mass of L* galaxies. We observe a fairly tight correlation between the derived stellar masses and the observed, rest--frame 1700 Å\ luminosity, with a typical scatter of 0.3 dex. Using this correlation, we are able to bound the total stellar mass density of all HDF--N galaxies with photometrically derived redshifts in this range.
Support for this work is provided by NASA through grant GO-07817.01-96A.