Spectroscopic and Photometric Nearby Field Galaxy Survey
Poster paper presented at IAU Symposium 171, June 26-30 1995,
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
- 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.
- 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 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.