GALAXY FORMATION IN LAMBDA-GREATER-THAN-0 FRIEDMANN MODELS - CONSEQUENCES FOR THE NUMBER COUNTS VERSUS REDSHIFT TEST

We study the effect of the cosmological constant Lambda on galaxy form ation using a simple spherical top-hat overdensity model. We consider models with Omega(0)=0.2, lambda(0)=0, and Omega(0)=0.2, lambda(0)=0.8 (where Omega(0) is the density parameter, and lambda(0)=Lambda/3H(0)( 2) where H-0 is the Hubble constant). We adjust the initial power spec trum amplitude so that both models reproduce the same large-scale stru ctures. The galaxy formation era in the lambda(0)=0 model occurs early (z similar to 6) and is very short, whereas in the lambda(0)=0.8 mode l the galaxy formation era starts later (z similar to 4), and last muc h longer, possibly all the way to the present. Consequently, galaxies at low redshift (z<1) are significantly more evolved in the lambda(0)= 0 model than in the lambda(0)=0.8 model. This result implies that prev ious attempts to determine Lambda using the number counts versus redsh ift test are probably unreliable.