Issue |
A&A
Volume 425, Number 3, October III 2004
|
|
---|---|---|
Page(s) | 813 - 823 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20040394 | |
Published online | 28 September 2004 |
Kinematics of tidal tails in interacting galaxies: Tidal dwarf galaxies and projection effects *,**
1
CEA/DSM/DAPNIA, Service d'Astrophysique, Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: Frederic.Bournaud@obspm.fr
2
Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014, Paris, France
3
École Normale Supérieure, 45 rue d'Ulm, 75005, Paris, France
4
CNRS FRE 2591
5
Observatoire Astronomique Marseille-Provence & Laboratoire d'Astrophysique de Marseille, 2 place Le Verrier, 13248 Marseille Cedex 04, France
Received:
5
March
2004
Accepted:
4
June
2004
The kinematics of tidal tails in colliding galaxies has been studied via Fabry-Pérot observations of the Hα emission. With
their large field of view and high spatial resolution, the Fabry-Pérot
data allow us to probe simultaneously, in 2D, two kinematical features of
the tidal ionized gas: large-scale velocity gradients due to streaming
motions along the tails, and small-scale motions related to the internal
dynamics of giant HII regions within the tails. In several interacting
systems, massive (10) condensations of HI, CO and stars are
observed in the outer regions of tails. Whether they are genuine
accumulations of matter or not is still debated. Indeed a part of the
tidal tail may be aligned with the line-of-sight, and the associated
projection effect may result in apparent accumulations of matter that does
not exist in the 3D space. Using numerical simulations, we show that
studying the large-scale kinematics of tails, it is possible to know
whether these accumulations of matter are the result of projection effects
or not. We conclude that several ones (Arp 105–South, Arp 242, NGC 7252,
and NGC 5291–North) are genuine accumulations of matter. We also study
the small-scale motions inside these regions: several small-scale velocity
gradients are identified with projected values as large as 50–100 km s-1 accross the observed HII regions. In the
case of NGC 5291–North, the spatial resolution of our observations is
sufficient to detail the velocity field; we show that this system is
rotating and self-gravitating, and discuss its dark matter content. The
Fabry-Pérot observations have thus enabled us to prove that some 109
condensations of matter are real structures, and are kinematically decoupled from the rest of the tail. Such massive and self-gravitating objects are the progenitors of the so-called “Tidal Dwarf Galaxies”.
Key words: galaxies: interaction / galaxies: formation / galaxies: evolution / galaxies: kinematics and dynamics
© ESO, 2004
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