Annu. Rev. Astron. Astrophys. 1998. 36: 189-231 Copyright © 1998 by Annual Reviews. All rights reserved

6. FUTURE PROSPECTS

The observations described in this review have provided us with the beginnings of a quantitative picture of the star formation properties and evolutionary properties of the Hubble sequence. However, the picture remains primitive in many respects, as it is based in large part on integrated, one-zone averages over entire galaxies and extrapolations from present-day SFRs to crude characterizations of past star formation histories. Uncertainties in fundamental parameters such as the IMF and massive stellar evolution undermine the accuracy of the entire SFR scale and weaken the interpretations that are based on these measurements. Ongoing work on several fronts should lead to dramatic progress over the next decade, however.

The most exciting current development is the application of the SFR diagnostics described in Section 2 to galaxies spanning the full range of redshifts and look-back times (Ellis 1997). This work has already provided the first crude measures of the evolution in the volume-averaged SFR (Madau et al 1996, 1998). The combination of 8- to 10-m class groundbased telescopes, HST, and eventually the Next Generation Space Telescope should provide detailed inventories of integrated spectra, SFRs, and morphologies for complete samples of galaxies at successive redshifts. This should give the definitive picture of the star formation history of the Hubble sequence and impose strong tests on galaxy formation and evolution models. At the same time, a new generation of IR space observatories, including the Wide-Field Infrared Explorer and Space Infrared Telescope Facility, will provide high-resolution observations of nearby starburst galaxies and the first definitive measurements of the cosmological evolution of the IR-luminous starburst galaxy population.

Although studies of the star formation histories of nearby galaxies are largely being supplanted by the more powerful look-back studies, observations of nearby galaxies will remain crucial for understanding many critical aspects of galaxy formation and evolution. Perhaps the greatest potential is for understanding the physical processes that determine the local and global SFRs in galaxies and understanding the feedback processes between the star formation and the parent galaxies. This requires spatially resolved measurements of SFRs over the full spectrum of insterstellar and star formation environments and complementary measurements of the densities, dynamics, and abundances of the interstellar gas. Uncertainty about the nature of the star formation law and the SFR-ISM feedback cycle remain major stumbling blocks to realistic galaxy evolution models, but observations over the next decade should provide the foundations of a physically based model of galactic star formation and the Hubble sequence.

ACKNOWLEDGMENTS

I wish to express special thanks to my collaborators in the research presented here, especially my current and former graduate students Audra Baleisis, Fabio Bresolin, Charles Congdon, Murray Dixson, Kevin Edgar, Paul Harding, Crystal Martin, Sally Oey, Anne Turner, and Rene Walterbos. During the preparation of this review, my research was supported by the National Science Foundation through grant AST-9421145.