Galactic Evolution and Cosmology: Probing the Cosmological Deceleration Parameter

Abstract

The magnitude-redshift relation, the color-redshift relation, the galaxy number count, the redshift distribution of galaxies, and the extragalactic background light are calculated taking into account the effect of galactic evolution for several values of the cosmological deceleration parameter q_0_ and the redshift of galaxy formation z_F_. The spectral evolutions of galaxies for five morphological types E/S0, Sab, Sbc, Scd, and Sdm are simulated on the basis of the models of Arimoto and Yoshii. According to recent observations of faint elliptical galaxies, the magnitude-redshift relation favors high q_0_ models, whereas the galaxy number count favors low q_0_ models. It is found that, without the effect of galactic evolution, these two observations cannot be reproduced simultaneously by a single value of q_0_. We show that this apparent inconsistency vanishes if the evolutionary brightening of early-type galaxies in the past is taken into account. All the existing data are compatible with the deceleration parameter q_0_ ~ 0.5 provided that galaxies are formed at redshift z_F_ ~ 3-5. The predicted near-IR background light is an order of magnitude lower in the energy flux than the recent observations by Matsumoto, Akiba, and Murakami so that it may be attributed to other origins.