A Caltech Library Service

Deep Optical Galaxy Counts with the Keck Telescope

Smail, Ian and Hogg, David W. and Yan, Lin and Cohen, Judith G. (1995) Deep Optical Galaxy Counts with the Keck Telescope. Astrophysical Journal, 449 (2). L105-L108. ISSN 0004-637X. doi:10.1086/309647.

[img] PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present faint galaxy counts from deep VRI images obtained with the Keck Telescope. These images reach R ~ 27 in median seeing FWHM ~ 0.”5-0.”6, and we detect a integrated galaxy number density of 7 × 105 deg-2, equivalent to 3 × 10^(10) galaxies in the observable universe. In addition we present median galaxy colors as a function of magnitude; bluing trends are visible in all colors to R ~ 24.5. Fainter than R ~ 24.5, however, the typical V - R color becomes redder again, V - I remains constant, and R - I becomes yet bluer. These trends are consistent with the VRI count slopes, implying a decrease in the V slope at the faintest levels, which our data support. Taking advantage of our good seeing we also present median half-light radii for faint galaxies; these show a steady decline at fainter magnitudes, leading to an intrinsic half-light radius of ~0 2 for a typical R ~ 26 galaxy. Irrespective of the redshift distribution, the extremely high galaxy surface densities and their small intrinsic sizes are consistent with a scenario in which the majority of the very faint field population are dwarf galaxies or subgalactic units.

Item Type:Article
Related URLs:
URLURL TypeDescription
Smail, Ian0000-0003-3037-257X
Hogg, David W.0000-0003-2866-9403
Yan, Lin0000-0003-1710-9339
Cohen, Judith G.0000-0002-8039-4673
Additional Information:© 1995 The American Astronomical Society. Received 1995 April 28; accepted 1995 June 15. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California. First, we thank Shri Kulkarni for his great generosity in allowing us to use these data. We acknowledge useful discussions and encouragement from Rebecca Bernstein, Roger Blandford, and Nigel Metcalfe. We also thank the referee, Richard Kron, for many helpful comments. Support via a NATO Advanced Fellowship and a Carnegie Fellowship (I. R. S.) and an NSF Graduate Fellowship (D. W. H.) is gratefully acknowledged. Finally, it is a pleasure to thank the W. M. Keck Foundation and its president, Howard B. Keck, for the generous grant that made the W. M. Keck Observatory possible.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
North Atlantic Treaty Organization (NATO)UNSPECIFIED
Carnegie Institution of WashingtonUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:cosmology: observations—galaxies: evolution—galaxies: photometry
Issue or Number:2
Record Number:CaltechAUTHORS:20170228-093233297
Persistent URL:
Official Citation:Ian Smail et al 1995 ApJ 449 L105
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74586
Deposited By: Tony Diaz
Deposited On:28 Feb 2017 18:37
Last Modified:11 Nov 2021 05:28

Repository Staff Only: item control page