Spectroscopic and Photometric Nearby Field Galaxy Survey

Poster paper presented at IAU Symposium 171, June 26-30 1995, Heidelberg


GALAXY EVOLUTION?

Galaxy evolution is one of the key questions in current astronomy. Recent observations of distant galaxies have provided surprising evidence for strong and recent evolution of cluster galaxies, as well as evidence for powerful starbursts in field galaxies. These observations conflict with previous ideas of orderly and early galaxy evolution. ( Litt.: e.g., Broadhurst et al. 1988; Tyson 1988; Colless et al. 1990; Koo and Kron 1992; Koo et al. 1993; Lilly 1993 )

PROBLEMS IN EVOLUTION TESTS

The galaxy evolution theories can be tested by comparing the images and spectra of galaxies at different redshifts, but two problems complicate this comparison.
  1. The distant galaxies subtend a small angle (~2 arcsec), and we unavoidably obtain integrated spectra of the whole galaxy. Nearby galaxies typically subtend more than 1 arcmin, and with a spectrograph slit width of a few arcsec we obtain spectra of only the central regions.
  2. Distant field galaxies have been generally selected by their blue magnitude, and this biases the samples towards intrinsically faint galaxies. The comparison of an ``average'' nearby galaxy and an ``average'' distant galaxy will be biased if no account is taken of their differences in mass, metallicity and star formation history.

THE REMEDY

The purpose of our study is to obtain an accurate description of the distribution of magnitude, structural parameters, color, and spectral type for a large number of field galaxies. The observed emission line strengths will allow us to measure the star formation rate in nearby galaxies with greater precision than was previously possible. In addition, we will use absorption line diagnostics to study the star formation history of these galaxies, as demonstrated by Caldwell et al. (1993) for galaxies in the Coma Cluster. The magnitude and structural parameters (effective radius and surface brightness) are necessary to calculate the detection rates at increasing redshift. These data will be used as an aid in understanding the spectra of galaxies at higher redshift, and in measuring the changes in star formation rates over time.


Back to overview poster