Science with the Hubble Space Telescope -- II
Book Editors: P. Benvenuti, F. D. Macchetto, and E. J. Schreier
Electronic Editor: H. Payne

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DEEP Keck Survey of Field Galaxies Imaged by HST

G. D. Illingworth, D. A. Forbes, R. Guzmán, A. C. Phillips and N. P. Vogt
UCO/Lick Observatory and Board of Astronomy and Astrophysics
University of California, Santa Cruz, CA 95064 USA

Abstract:

Some initial results are shown from deep, multi-slit Keck spectroscopy of high-redshift field galaxies in HST WFPC2 images. This includes a gravitational lens candidate at a redshift , a large edge-on disk galaxy at the same redshift, as well as velocity widths for disk galaxies over the redshift range compared to the local Tully-Fisher relation.

Keywords: faint galaxies, high redshifts

Overview

The DEEP project (Deep Extragalactic Evolutionary Probe) is a multi-year program using the 10-m Keck telescope to conduct a large-scale survey of distant, faint, field galaxies in regions that have been imaged by HST (see, e.g., the paper by Koo in this volume, and references therein). The broad scientific goal is to understand how galaxies and their distribution in space have evolved out to redshifts z>1, and the mechanisms of that evolution. The DEEP team currently is undertaking a survey of the properties of distant galaxies using the Keck first-generation HIRES and LRIS spectrographs in areas for which HST WFPC2 images are available.

Together these data provide redshifts, internal velocities, metallicity indices, colors, magnitudes, sizes and surface brightnesses. The internal kinematical measurements, i.e., rotation curves and velocity widths, provide a new and very powerful dimension to studies of the degree of evolution with look-back time, since they are not dependent on luminosity (see e.g., Forbes et al. 1996, Guzmán et al. 1996, and Vogt et al. 1996). In particular, they can provide estimates of mass, when size and inclination are determined from HST images. Evolution is assessed by comparing the physical properties of distant galaxies with their nearby counterparts of similar kinematical characteristics.

Some of the data and results obtained in this initial stage of the DEEP project are shown in Figure 1 for two high redshift galaxies. The elliptical in Figure 1a appears to be lensing a distant object (at ---see Crampton et al. 1996; see also Ratnatunga et al. 1996). Measurement of the stellar velocity dispersion should be practical for the lensing object. The disk galaxy in Figure 1b shows the potential for measurement of rotation curves for distant galaxies. Such measurements have been made for a larger sample and the results summarized in Figure 2 (see Vogt et al. 1996).

Acknowledgments:

These results are contributions from a team effort that involves the authors as well as S. Faber, C. Gronwall, E. Groth, D. Koo and K. Wu, plus other members of the DEEP team. This project is being carried out under the auspices of the Berkeley Center for Particle Astrophysics. Funding for this work was provided by NSF grants AST91-20005 and AST-8858203, and NASA grants AR-5801.01-94A and GO-2684.05-87A. R. G. acknowledges funding from the Spanish MEC fellowship EX93-27295297.

 
Figure: The large data points in this plot of luminosity versus velocity width represent galaxies with spatially-resolved rotation curves. Eight of these galaxies were observed spectroscopically with the Keck telescope, while two are from Vogt et al. (1993). HST WFPC2 images of the galaxies provided structural and geometrical parameters (disk scale lengths, inclination and major axis PA). Final velocities were obtained by matching observed spectra to simulated emission line spectra which included the effects of finite slit width, slit misalignment and seeing (Vogt et al. 1996). The smaller data points represent galaxies with line-width measurements (Forbes et al. 1996). Error bars are representative of the two approaches. The lines show the local Tully-Fisher relationship of Pierce & Tully (1988), and a 2 dispersion about it. The sample is split at . We find no evidence for strong evolution in the M/L ratios of the galaxies in either the low or the high redshift sample, though we note that both samples are quite limited in size. Our data constrain luminosity increases to be < 1 magnitude at --1.

References:

Crampton, D., Le Fèvre, O., Hammer, F., & Lilly, S. J. 1996, A&A, in press

Forbes, D. A., Phillips, A. C., Koo, D. C., & Illingworth, G. D. 1996, ApJ, in press

Groth, E. J. et al. 1996, in preparation

Guzmán, R. et al. 1996, ApJ, 460, L5

Pierce, M. J. & Tully, R. B. 1988, ApJ, 330, 579

Ratnatunga, K. U., Ostrander, E. J., Griffiths, R. E., & Im, M. 1995, ApJ, 453, L5

Vogt, N. P., Herter, T., Haynes, M. P., & Courteau, S. 1993, ApJ, 415, L95

Vogt, N. P. et al. 1996, ApJ, in preparation