Gaseous Substructure in Tidal Tails and the Formation of Tidal Dwarf Galaxies

John Hibbard, NRAO
Josh Barnes, Institute for Astronomy
Thijs van der Hulst, Kapteyn Astronomical Institute

To be submitted to AJ
Go here for more figures on NGC 4038/9 and here for more details on the HI observations

We use our recent HI and optical observations of the well known interacting system NGC 4038/9, "The Antennae", to explore the nature of the gaseous substructures found within its extensive tidal tails, including the putative tidal dwarf galaxy at the end of the southern tail. We analyze about a dozen HI concentrations within the tails, finding that they do not distinguish themselves from interclump regions in terms of their HI linewidths, optical surface brightness, or optical colors. We do find evidence that one of the star-forming regions within the tidal dwarf contains enough luminous mass to be self-gravitating, with a virial mass of 1.1E8 Mo, but this derivation involves significant uncertainties. The other gaseous concentrations are either not self-gravitating, or must be bound by non-luminous matter. We extend other tidal dwarf galaxy candidates reported in the literature with similar kinematic data. We find that TDG as a class do not contain enough luminous matter to bind them. Previous work reached the opposite conclusion by combining luminous mass indicators and dynamical linewidths in an unphysical manner. Additionally, many of the TDGs with high inferred luminous-to-dynamical masses are subject to projection effects, where tidal material piles up along the line of sight.

Paper: tex file; ps.gz of text & figs (590 kB)