The Contribution of Low-Surface-Brightness Galaxies to Faint Galaxy Number Counts

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Session 71 -- Galaxy and CBR Distribution
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[71.01] The Contribution of Low-Surface-Brightness Galaxies to Faint Galaxy Number Counts

H.C.Ferguson (STScI), S.S.McGaugh (IoA)

Low surface-brightness galaxies are systematically underrepresented in most low-redshift galaxy surveys, and in particular in all surveys used to date to compute the local field-galaxy luminosity function. However, deep surveys probe to much deeper isophotal levels, and hence could in principle include low-surface-brightness galaxies missed in the local surveys.

To explore the consequences of including low-surface-brightness (LSB) galaxies, we use a Monte-Carlo approach to construct catalogs of simulated non-evolving galaxies drawn from a multivariate distribution of galaxy luminosities, central surface brightnesses, bulge/disk ratios and spectral-energy distributions. For each galaxy, we compute seeing-convolved surface-brightness profiles in various passbands, and determine whether or not to count the galaxy based on isophotal selection criteria that closely match those used for real surveys. We find it possible to include a large population of LSB galaxies and incorporate a steep faint-end slope of the luminosity function in our simulations without violating the observed constraints on the local field-galaxy luminosity function or the HI mass function.

The discrepancy between the observed deep $B$-band galaxy counts and the predictions of a non-evolving model with $q_0 = 0.5$ is greatly reduced when this LSB population is included and the galaxies are selected based on isophotal limits. The agreement between the counts and the models is still better with lower values $q_0$. The redshift distribution in the $B$ band remains roughly consistent with that observed to $B=24$.

Support for this work was provided by the Science and Engineering Research Council and by NASA through grant HF1043 awarded by the Space Telescope Science Institute which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS5-26555.

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