Long tidal tails in merging galaxies and their implications

Abstract

We investigate the properties of long tidal tails using the largest to date sample of 461 merging galaxies with $\log (M_\ast /\rm M_\odot )\ge 9.5$ within 0.2 ≤ z ≤ 1 from the COSMOS survey in combination with Hubble Space Telescope imaging data. Long tidal tails can be briefly divided into three shape types: straight (41 per cent), curved (47 per cent) and plume (12 per cent). Their host galaxies are mostly at late stages of merging, although 31 per cent are galaxy pairs with projected separations d > 20 kpc. The high formation rate of straight tidal tails needs to be understood as the projection of curved tidal tails accounts for only a small fraction of the straight tails. We identify 165 tidal dwarf galaxies (TDGs), yielding a TDG production rate of 0.36 per merger. Combined with a galaxy merger fraction and a TDG survival rate from the literature, we estimate that ∼ 5 per cent of local dwarf galaxies are of tidal origin, suggesting the tidal formation is not an important formation channel for the dwarf galaxies. More than half of TDGs are located at the tip of their host tails. These TDGs have stellar masses in the range of $7.5\le \log (M_\ast /\rm M_\odot )\le 9.5$ and appear compact with half-light radii following the M* - Re relation of low-mass elliptical galaxies. However, their surface brightness profiles are generally flatter than those of local disc galaxies. Only 10 out of 165 TDGs have effective radii larger than 1.5 kpc and would qualify as unusually bright ultra-diffuse galaxies.

Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago

“…1E). Tidal-tail features in a galaxy merger are expected occur on larger scales (>10 kpc) (6,31). We therefore disfavor, but cannot completely rule out, a tidal-tail origin for the observed spiral morphology.…”

A diffuse tidal dwarf galaxy destined to fade out as a “dark galaxy”

“…However, its high metallicity and its location at the end of an H i tail makes HCG 16-LSB1 compatible with a recently formed TDG. Strikingly, systematic detections of TDGs show compactclumpy morphologies with bright surface brightnesses (e.g., Ren et al 2020), contrary to that of HCG 16-LSB1. The dark matter content of HCG 16-LSB1 also appears anomalous for a TDG, with a calculated mass-to-light ratio in the range M/L = [3, 10].…”

Are Disks of Satellites Comprised of Tidal Dwarf Galaxies?

“…Tidal dwarf galaxies form in tidal tails of interacting galaxies. Their stellar masses can reach 10 9.5 M , particularly at high redshifts [32]. Such an origin of the satellites would naturally explain the anisotropic distributions of their position and velocities as well as some satellites being counter orbiting [33].…”

“…Reference [105] also compared effective radii of the satellites inside and outside of the disk of satellites of Andromeda and found no difference. Perhaps surprisingly, tidal dwarf galaxies actually follow the mass-radius relation of usual dwarf galaxies [32,107]. Reference [32] found that young tidal dwarf galaxies have flatter photometric profiles than standard dwarfs, but this might be because these objects are still assembling.…”

“…Perhaps surprisingly, tidal dwarf galaxies actually follow the mass-radius relation of usual dwarf galaxies [32,107]. Reference [32] found that young tidal dwarf galaxies have flatter photometric profiles than standard dwarfs, but this might be because these objects are still assembling. Reference [105] neither found a difference in the mass-velocity dispersion relation for the in-plane and off-plane satellites of Andromeda, but this is what we expect with MOND [80,81].…”