||The Space Density Evolution of Wet and Dry Mergers in the Canada-France-Hawaii Telescope Legacy Survey
||477, Galaxy Mergers in an Evolving Universe
||Chou, R. C. Y.; Bridge, C. R.; Abraham, R. G.
||We analyze 1298 merging galaxies with redshifts up to
z = 0.7 from the Canada-France-Hawaii Telescope Legacy Survey, taken from the
catalog presented in Bridge et al. (2010).
By analyzing the internal colors of these systems, we show that
so-called wet and dry mergers evolve in different senses, and
quantify the space densities of these systems.
The local space density of wet mergers is essentially identical to the local
space density of dry mergers. The
evolution in the total merger rate is
modest out to z ∼ 0.7, although the wet and dry
populations have different
evolutionary trends. At higher redshifts
dry mergers make a smaller contribution to the
total merging galaxy population, but this is
offset by a roughly equivalent increase in the contribution
from wet mergers.
By comparing the mass density function of early-type galaxies
to the corresponding mass density function for merging systems,
we show that not all the major mergers with the highest masses (Mstellar > 1011M☉) will end up with the most massive
early-type galaxies, unless the merging timescale is dramatically longer
than that usually assumed. On the other hand, the usually-assumed merging
timescale of ∼ 0.5–1 Gyr is quite consistent with the data if we
suppose that only less massive
early-type galaxies form via mergers.
Since low-intermediate mass ellipticals
are 10–100 times more common than their most massive counterparts, the hierarchical
explanation for the origin of early-type galaxies may be correct for the vast majority of
early-types, even if incorrect for the most massive ones.