Multiple-passband Hubble Space Telescope galaxy and pair counts as tests of galaxy evolution history.

摘要

The author constructs an empirical model of galaxy population evolution. This model properly includes the effects of binary galaxy merging, which is assumed having been occurring in galaxy pairs as those observed in the nearby universe. The model also considers the stellar population evolution that overall follows the traditional scenarios in astrophysics. The model uses the properties of galaxies or galaxy pairs in the nearby universe as the boundary conditions, traces back the galaxy evolution history, and predicts galaxy populations at earlier cosmological epochs. Such predictions are compared to multiple-passband counts of faint galaxies and galaxy pairs, mainly from the high-resolution observations with the Hubble Space Telescope, under the constraint that the model can be consistent with the statistical data on elliptical galaxies (including lenticular galaxies) in the nearby universe. The joint comparison yields the evidence that almost all nearby elliptical galaxies are the remnants of galaxy merging, and shows that overall traditional stellar population evolution together with mild galaxy merging can sufficiently explain the current observational data about faint galaxies at cosmological redshifts $z\lesssim$ 1 to 2 in a universe with a zero cosmological constant. Therefore, this study shows no necessity for a nonzero cosmological constant or exotic star formation processes in explaining the current statistical data about faint galaxies. The comparison also indicates a significant role of galaxy merging in the early evolution history of galaxies.