Structure and photometry of an I < 20.5 galaxy sample from the Hubble Space Telescope medium deep survey

Andrew C. Phillips, Matthew A. Bershady, Duncan A. Forbes, David C. Koo, Garth D. Illingworth, David B. Reitzel, Richard E. Griffiths, Rogier Windhorst

Research output: Contribution to journalReview articlepeer-review

8 Scopus citations


A set of 100 faint galaxies from nine Hubble Space Telescope Wide Field Camera I-band images have been analyzed as part of the Medium Deep Survey (MDS) Key Project. This sample reaches a depth of I ≲ 20.5 (corresponding to B ∼ 22-23) and complements the first set of fainter galaxies analyzed by the MDS team. Images were deconvolved using the Lucy-Richardson algorithm and a newly developed procedure designed to yield a more reliable determination of structure in the low-S/N regime. These deconvolved images were used to characterize the structure of the galaxies through quantitative measurements of total magnitudes, half-light radii, exponential disk scale lengths, and disk-to-total ratios. Extensive testing was done to establish the validity of the procedures used and to characterize the degree of systematic errors present in the analysis techniques. The observed size-magnitude distributon appears consistent with a scenario in which luminous galaxies have evolved little in intrinsic luminosity, size, or structure over recent epochs in a "normal" cosmology (0 < q0 < 0.5 and Λ0 = 0). The predicted nonevolving distributions were based on models designed to fit existing counts, colors, and redshifts of faint galaxies and on the observed correlations between metric rest-frame size and luminosity found in a nearby galaxy sample studied by Kent (1984, 1985). The typical galaxy in our sample is expected to be at z ≃ 0.3, and to have a luminosity ∼0.5 mag fainter than L* and a half-light radius of ∼ 1″ or ∼6 kpc (H0 = 50 km s-1 Mpc-1). The observed distribution of disk-to-total ratios, while uncertain, is in agreement with that of Kent's sample and thus supports the view that substantial evolution has not occurred over the look-back times characteristic of our sample.

Original languageEnglish (US)
Pages (from-to)21-40
Number of pages20
JournalAstrophysical Journal
Issue number1
StatePublished - May 1 1995


  • Cosmology: observations
  • Galaxies: fundamental parameters
  • Galaxies: photometry
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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