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Session 84 - IGM.
Display session, Friday, January 09
Exhibit Hall,

[84.06] The Distribution of High Redshift Galaxy Colors: Line of Sight Variations in Neutral Hydrogen Absorption

J. M. Geoffroy, J. C. Charlton (Penn State), M. A. Bershady (U. Wisconsin/Penn State)

In order to accurately map the formation and evolution of galaxies, it is essential to assemble complete samples of galaxies over a wide range of redshifts. Galaxies at the highest redshifts (z > 2) are currently selected by virtue of their colors falling within specific regions of color-color diagrams. These regions have been confirmed spectroscopically to contain high redshift galaxies at high reliability. However, the fraction of high redshift objects contained in these regions, i.e. the selection completeness, is less well defined. Even for a single galaxy spectral energy distribution (SED), variations in the intervening absorption between different lines of sight create a distribution of possible colors, some of which may fall outside the selected region of color-color diagrams and be overlooked. To quantify the completeness of high-redshift galaxy selection via colors, we model galaxy colors from 1.75 < z < 5 via Monte Carlo simulations of the intervening neutral hydrogen absorbers, i.e. Ly\alpha forest and Lyman limit systems. We present distributions of colors which are systematically different in both mean color and scatter from those predicted by Madau's (1995, ApJ, 441, 18) analytic approximations. We also compare the color distributions that result from different possible absorber column density and Doppler parameter distributions. As one application of our analysis we consider the sample completeness as a function of redshift for a particular SED, given the multi-color selection boundaries for the Hubble Deep Field proposed by Madau et al. (1996, MNRAS, 280, 67). We conclude that models of the variation of colors due to intervening absorbers must be applied to an ensemble of SEDs and redshifts in order to accurately derive the z > 3 luminosity function.

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