THE LUMINOSITY, STELLAR MASS, AND NUMBER DENSITY EVOLUTION OF FIELD GALAXIES OF KNOWN MORPHOLOGY FROM z = 0.5 TO 3

摘要

The evolution of rest-frame B-band luminosities, stellar masses, and number densities of field galaxies in the Hubble Deep Fields North and South are studied as a function of rest-frame 5-band morphological type out to redshift z ～ 3 using a sample of 1231 I< 27 galaxies with spectroscopic and photometric redshifts. We find that the comoving and relative number densities of ellipticals and spirals decline rapidly at z > 1, although examples of both types exist at z > 2. The number and number fraction of peculiar galaxies consistent with undergoing major mergers rise dramatically and consistently at redshifts z > 2. Through simulations we argue that this change is robust at the 4 a level against morphological K-corrections and redshift effects. We also trace the evolution of rest-frame B-band luminosity density as a function of morphology out to z ～ 3, finding that the luminosity density is steadily dominated by peculiars at z > 1.5 with a peak fraction of 60%-90% at z ～ 3. By z ～ 0.5, B-band luminosity fractions are similar to their local values. At z ～ 1 the 5-band luminosity densities of ellipticals and spirals are similar, with a combined contribution of ～90% of the total luminosity at z < 1. The stellar mass density follows a trend similar to that of the luminosity density, with some important exceptions. At high redshifts, z > 2, 60%-80% of stellar mass appears attached to peculiars, while at z < 1, 80%-95% of stellar mass is attached to ellipticals and spirals. The total integrated stellar mass density of peculiars slightly declines at lower redshift, suggesting that these systems evolve into normal galaxies. In contrast to the luminosity density, the stellar mass density of ellipticals is greater than spirals at z < 1, and the stellar masses of both types grow together at z < 1, while number densities remain constant. From a structural analysis of these galaxies we conclude that galaxy formation atz > 2 is dominated by major merging, while at z < 1 the dominate modes are either minor mergers or quiescent star formation produced by gas infall. Finally, at z ～ 1.5 the comoving luminosity, mass, and number densities of spirals, ellipticals, and peculiars are nearly equal, suggesting that this is the "equilibrium" point in galaxy evolution and an important phase transition in the universe's history.