Galaxy Evolution at 0 < z < 2 from the NICMOS HDF-North

Abstract

We have carried out a deep infrared imaging survey (1.1um and 1.6um) of the Hubble Deep Field North (HDF-N) using NICMOS on board the Hubble Space Telescope. The combined WFPC2+NICMOS data set lets us study galaxy morphologies, colors and luminosities at common rest frame wavelengths over a broad range of redshifts, e.g., in the V-band out to z=2. Here, I illustrate some applications of this data set for studying the evolution of giant galaxies, on and off the Hubble Sequence. Large, relatively ordinary spiral galaxies are found out to at least z=~1.25. Morphological irregularities seen in many distant HDF galaxies tend to persist from ultraviolet through optical rest frame wavelengths, suggesting that these are genuinely peculiar, structurally disturbed systems. Red giant ellipticals are found out to (photometric) redshifts z=~1.8, implying that some such galaxies probably formed the bulk of their stars at z_f>~4. However, there are also bluer early type galaxies at z>0.5, which may have experienced extended star formation histories. Finally, there appears to be a substantial deficit of high luminosity galaxies of all types at 1.4<~z<2 compared to lower redshifts. However, this result must be considered with caution given the small volume of the HDF, its susceptibility to line-of-sight clustering variations, and the heavy reliance on photometric redshifts at z>~1.4.