(5a) Galaxy Formation and Number Counts in Lambda > 0
Friedmann Universes
Martel (1994) studied the applicability of the number counts vs
redshift test to models with a nonzero cosmological constant Lambda.
This test is based
on the fact that the variation of the comoving volume element dV with redshift
depends on the value of the Lambda. The most direct way to apply this method
is to count galaxies and bin them in redshift. In doing so, we must take
into account the fact that the presence of a cosmological constant might
affect the history of galaxy formation and luminosity evolution, a fact that
was overlooked by previous authors. Using the spherical infall model, we
showed that the presence of Lambda deeply affects the history of galaxy
formation, by delaying the epoch of galaxy formation. This results in nearby
galaxies (z < 1) being younger and therefore less evolved, making the number
counts versus redshift test inapplicable in its current form.