%0 Journal Article
%T Tidal Dwarf Galaxies and Missing Baryons
%A Frederic Bournaud
%J Advances in Astronomy
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/735284
%X Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble ˇ°normalˇ± dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the ˇ°missing baryons,ˇ± known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, ˇ°dark matterˇ± is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and ˇ°missing baryonsˇ± or ˇ°dark baryonsˇ± is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to ˇ°dark matterˇ±. 1. Introduction: The Formation of Tidal Dwarf Galaxies Tidal dwarf galaxy (TDG) is, per definition, a massive, gravitationally bound object of gas and stars, formed during a merger or distant tidal interaction between massive spiral galaxies, and is as massive as a dwarf galaxy [1] (Figure 1). It should also be relatively long-lived, so that it survives after the interaction, either orbiting around its massive progenitor or expelled to large distances. This requires a lifetime of at least 1 gigayear, and a transient structure during a galaxy interaction would not deserve to be considered as a real TDG. The formation of TDGs in mergers has been postulated for decades [2], including potential candidates in the Antennae galaxies (NGC4038/39) [3], and became an increasingly active research topic after the study of these tidal dwarf candidates by Mirabel et al. [4]. Figure 1: NGC7252 (a) is a recent merger of two spiral galaxies into a partially-relaxed central spheroidal galaxy. Two massive TDGs are found near the tip of the two long tidal tails (blue = HI, pink = H ¨C image courtesy of Pierre-Alain Duc). AM 1353-272 (b) does not have prominent, massive TDGs at the tip of tidal tails, but has instead may lower-mass objects all along its tail [ 5]. The bright spot on the northern tail is a foreground star. Tidal tails are a common feature in galaxy interactions.
%U http://www.hindawi.com/journals/aa/2010/735284/