Spectroscopic and Photometric Nearby Field Galaxy Survey

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


On this poster we report the progress of our spectral and imaging survey of nearby field galaxies.
This survey will be used to obtain an accurate description of star formation rates and star formation history of galaxies in the nearby universe and will serve as a benchmark for interpreting the spectra and number counts of distant galaxies.
At this time, about 40% of the observations have been obtained.


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 )


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 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.


Because many galaxy properties like color, star formation rate and emission line strength correlate with magnitude (e.g. Moody and Kirshner 1988), our sample must span a broad range in absolute magnitude. As a result, we want to avoid a purely magnitude or diameter limited sample. We chose a mixed approach: we selected galaxies from the first CFA redshift catalogue, which contains galaxies to a limiting magnitude of m_B=14.5 (Huchra et al. 1983). We calculated the absolute magnitude for each galaxy, and put galaxies in 1 magnitude bins. We then drew galaxies from each bin so that the magnitude distribution approximated the observed galaxy luminosity function. Thus, of the 1006 galaxies that met our selection criteria, 196 galaxies remained.
Our sample containes galaxies with the desired range of absolute magnitudes (-14 < M_B < -22), extending five magnitudes fainter than the chararacteristic luminosity L* ~ -19.2 (de Lapparent et al. 1989).


We are in the process of obtaining integrated spectra at higher resolution (4.5-6.0 Å ) and for a larger sample (196) than is available in the literature (e.g. Kennicutt 1992). The FAST spectrograph at the F.L.Whipple Observatory's 60'' Telescope (Mt. Hopkins, Arizona) is mounted with a thinned Loral 2720 x 512 CCD giving a spectral range of either 3250--7250Å or 3600--7500Å at 1.5Å per pixel and a total throughput of telescope, spectrograph and CCD of ~ 55% at 4800Å .
Integrated spectra are obtained by aligning the slit with the major axis of the galaxy, and moving the galaxy across the slit over a total angular distance of 0.5D_25 (the blue isophotal diameter), allowing us to properly weight the faint outer areas of the galaxy. (We reduce the overhead of the current manual instrument rotator by grouping the galaxies by the position angle of the major axis.) To reduce effective read-out-noise we bin the CCD at read-out by 8 pixels in the spatial direction. We also obtain an exposure centered on the nucleus, to determine the nuclear characteristics.
We are also in the process of obtaining B and R filter images using the Loral 2048 x 2048 CCD camera at the Cassegrain focus of the FLWO 48'' Telescope. U images will be obtained later when the thinned 4-Shooter will have become available.


(of the four galaxies shown on this poster)
  GALAXY NAME    UGC #    V_LG      M_B     TYPE
  A 1159+6237    7009     1120    -15.98     10
  A 1552+1645   10086     2206    -17.31     -2
  A 1531+6744    9896     6461    -19.72      5A
  IC 4213        8280      815    -15.58      5A

Table 1: Cross-reference to the UGC catalog, velocity with respect to the Local Group (km/sec), absolute blue magnitude for H0=100 km/sec/Mpc and numerical type for the four galaxies presented here.


Broadhurst T. J., Ellis, R. S. & Shanks, T. 1988, MNRAS 235, 827
Caldwell, N., Rose, J., Sharples, R., Ellis, R. & Bower, R. 1993, AJ 106, 473
Colless, M., Ellis, R. S., Taylor, K., & Hook, R. N. 1990, MNRAS 244, 408
de Lapparent, V., Geller, M. J. & Huchra, John P. 1989, ApJ 343, 1
Huchra, J., Davis, M., Latham, D. & Tonry, J. 1983, Ap J Sup 52, 89
Kennicutt, R. 1992, ApJ, 388, 310.
Koo, D.C. & Kron, R.G. 1992, ARAA 30, 613
Koo, D.C., Gronwall, C. & Bruzual, G. A. 1993, ApJ L 415, L21
Lilly, S.J. 1993, ApJ 411, 501
Moody, J. W. & Kirshner, R. P., 1988, AJ 95, 1629
Tyson 1988, AJ 96, 1

Back to overview poster