Abstract
A newly developed isochrone synthesis algorithm for the photometric evolution of galaxies is described. Two initial mass functions and three photometric transformations are used to compute the B - V and V - K color index evolution. Non-negligible differences are observed among different models.
In the framework of the galaxy count model by Colín, Schramm, & Peimbert a simple merging scenario is considered to account for the excess of galaxies observed in the blue band counts. The excess is explained by the number and luminosity evolution of a group of galaxies called interacting, I. It is assumed that the number of I galaxies increases as (1 + z)
η due to mergers. Moreover, it is proposed that their characteristic luminosity increases as (1 + z)
3 due to starbursts driven by galaxy-galaxy collision and decreases as (1 + z)
-η due to the change in the size of the galaxies. A model with 7' η = 4.0 predicts that about 17% of the galaxies at z = 0.4 are interacting. Number evolution models with a rather high value of η fit better the data; in particular, the model with η = 4.0 predicts that about 13% of the galaxies have z > 0.7 in the 21.0 < m
bj < 22.5 interval, this contrasts with the upper bound of 5% obtained by Colless et al. (1990,1993). The excess of high redshift galaxies cannot be simply explained by changing reasonably the parameters of the luminosity function of I galaxies. This result could indicate that mergers are not the whole story.
