STScI Preprint #1273

New and Old Tests of Cosmological Models and Evolution of Galaxies

We describe the classical cosmological tests, such as the LogN-LogS, redshift-magnitude and angular diameter tests, and propose some new tests of the evolution of galaxies and the universe. Most analyses of these tests treat the problem in terms of a luminosity function and its evolution. The main thrust of this paper is to show that this is inadequate and can lead to a incorrect conclusions when dealing with high redshift sources. We develop a proper treatment in three parts.

In the first part we describe these tests based on the isophotal values of the quantities such as flux, size or surface brightness. We show the shortcomings of the simple point source approximation based solely on the luminosity function and consideration of the flux limit. We emphasize the multivariate nature of the problem and quantify the effects of other selection biases due to the surface brightness and angular size limitations. In these considerations the surface brightness profile, and the distribution of the basic parameters describing it, play a critical role in modeling of the problem. In general, in the isophotal scheme the data analysis and its comparison with the model predictions is complicated. In the second part we show that considerable simplification is achieved if these test are carried out in some sort of metric scheme, for example that suggested by Petrosian (1976). This scheme, however, is limited to well resolved sources. Finally, we describe the new tests and compare them to the traditional tests demonstrating the observational and modeling ease that they provide. These new procedures, which can use the data to a fuller extent than the isophotal or metric based tests, amount to simply counting the pixels or adding their intensities as a function of the surface brightness of all galaxies instead of dealing with surface brightnesses, sizes and fluxes (or magnitudes) of individual galaxies. We also show that the comparison of the data with the theoretical models of the distributions and evolution of galaxies has the simplicity of the metric test and utilizes the data as fully as the isophotal test.

Status:

Appeared in: The Astrophysical Journal, 507:1-15, 1998

Affiliations:

Space Telescope Science Institute, Baltimore, MD 21218 and Center for Space Science and Astrophysics, Stanford University, Stanford, CA 94305