paper

The first galaxies: structure and stellar populations

arXiv:astro-ph/0004028 · doi:10.1098/rsta.2000.0626

Abstract

The Hubble Deep Fields continue to be a valuable resource for studying the distant universe, particularly at z>2 where their comoving volume becomes large enough to encompass several hundred L* galaxies or their progenitors. Here I present recent results from a near-infrared imaging survey of the HDF-North with NICMOS, which provides structural and photometric information in the optical rest frame (4000-5500A) for hundreds of ordinary galaxies at 2<z<3, and which offers the means to search for still more distant objects at z>>5. Lyman break galaxies at 2<z<3 are compact and often irregular in the NICMOS images; ordinary Hubble sequence spirals and ellipticals seem to be largely absent at these redshifts, and apparently reached maturity at 1<z<2. The Lyman break galaxies have UV-optical spectral energy distributions like those of local starburst galaxies. Population synthesis models suggest typical ages ~few x 10^8 years and moderate UV extinction (~1.2 mag at 1700A), but the constraints are fairly weak and there may be considerable variety. Considering a near-IR selected galaxy sample, there is little evidence for a significant number of galaxies at z~3 that have been missed by UV-based Lyman break selection. Using the well-characterized z~3 galaxy population as a point of reference, I consider Lyman break galaxy candidates at 4.5<z<9, as well as one remarkable object which might (or might not) be at z>12. The space density of UV-bright galaxies in the HDF appears to thin out toward larger redshifts, although surface brightness selection effects may play an important role.

To appear in the Philosophical Transactions of the Royal Society, Series A. 19 pages with 9 encapsulated figures (11 postscript files). Latex, rspublic.cls file included

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