We present the results of our analysis of the geometrical tidal tail
characteristics for nearby and distant interacting galaxies. The sample
includes more than two hundred nearby galaxies and about seven hundred distant
ones. The distant galaxies have been selected in several deep fields of the
Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS) and they are at mean
redshift z=0.65. We analyze the distributions of lengths and thicknesses for
the tidal structures and show that the tails in distant galaxies are shorter
than those in nearby ones. This effect can be partly attributed to
observational selection effects, but, on the other hand, it may result from the
general evolution of the sizes of spiral galaxies wih z. The location of
interacting galaxies on the galaxy luminosity ($L$) -- tidal tail length ($l$)
plane are shown to be explained by a simple geometrical model, with the upper
envelope of the observed distribution being $l \propto \sqrt{L}$. We have
solved the problem on the relationship between the observed distribution of
tail flattening and the tail length in angular measure by assuming the tidal
tails to be arcs of circumferences visible at arbitrary angles to the line of
sight. We conclude that the angular length of the tidal tails visually
distinguished in nearby and distant galaxies, on average, exceeds 180 degrees.Comment: 8 pages, 7 figures; Astron.Lett. vol.37, 201
The morphologies of galaxies in several deep fields (HDF-N, HDF-S, HUDF, GOODS, GEMS) of the Hubble Space Telescope are analyzed visually. Lists are made of the galaxies with tidal structures (tails, bridges) and type M51 galaxies in these fields. Photometric characteristics and estimated redshifts for most of these objects are found in the published literature. A total of 29 candidate type M51 galaxies and 381 galaxies with tidal structures are discovered in three of the fields (HDF-N, HDF-S, HUDF). More than two hundred interacting galaxies are found in the regions of each of the GOODS and GEMS projects.
We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as ∝ (1 + z) m , where m ≈ 2.6. According to our estimates, over the last 6-7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M (B) ≤ −18 m must have undergone strong gravitational perturbations and mergers and ∼1/10-1/5 of the galaxies have accreted relatively low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the timescale on which a distant galaxy appears peculiar with growing z can increase considerably the estimated rate of mergers.
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