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A. M. Hopkins, A. J. Connolly (University of Pittsburgh)
A full understanding of galaxy evolution and development cannot be complete without an investigation of how star formation processes shape or modify galaxy morphologies. We have initiated such a study using deep NICMOS images of star forming galaxies spanning 0.7 < z <1.8. Galaxies in this era are undergoing what is probably the most rapid period of star-formation in their evolution, indicated by a significant change in the slope of the global luminosity density between 1 < z < 2. This redshift range also sees the development of disk structure in galaxies. Beyond z ~2 very few disk galaxies are seen, with the dominant population being irregular or amorphous galaxies. By z ~ 1 classical spiral disk morphologies have developed, and the irregular higher-redshift objects may be the progenitor population of these galaxies. Together these results strongly suggest that 1 < z < 2 is the era on which to focus for studying what relationships might exist between the detailed processes of star-formation and the formation or evolution of galaxy disks.
Our study of the morphologies of star-forming galaxies in this era is based on NICMOS deep imaging and grism data for 6 fields in the region of the Groth strip. The grism observations identify 37 sources as probable H-alpha emission systems, with corresponding star formation rates ranging from a few up to ~15 solar masses per year (although no corrections for extinction effects have been made). We have applied bulge-disk decompositions to estimate the disk component for the star forming objects. Here we present our analysis of the relationship between redshift, star-formation rate, and galaxy disk evolution during this formative era of galaxy development.
Support for this work was provided by NASA through grants GO-07871.02-96A and NRA-98-03-LTSA-039 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.
The author(s) of this abstract have provided an email address for comments about the abstract: ahopkins@phyast.pitt.edu