Issue |
A&A
Volume 472, Number 2, September III 2007
|
|
---|---|---|
Page(s) | 421 - 433 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20066760 | |
Published online | 26 June 2007 |
Search for tidal dwarf galaxy candidates in a sample of ultraluminous infrared galaxies
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: amonreal@aip.de
2
Instituto de Estructura de la Materia (CSIC), Serrano 121, 28006 Madrid, Spain e-mail: [colina;arribas;maca]@damir.iem.csic.es
Received:
17
November
2006
Accepted:
28
May
2007
Context.Small star-forming galaxies made out of collisional debris have been found in a variety of merging systems. So far only a few of them are known in Ultraluminous Infrared Galaxies (ULIRGs) although they show clear signs of interactions. Whether external star formation may take place in such objects in an open question.
Aims.The aim of this paper is to identify and characterise the physical and kinematic properties of the external star-forming regions in a sample of ULIRGs, including Tidal Dwarf Galaxies (TDG) candidates. The likelihood of survival of these regions as TDGs is also evaluated.
Methods.The analysis is based on optical Integral Field Spectroscopy (IFS) and high angular resolution Hubble Space Telescope (HST) imaging.
Results.We found that the presence of external star-forming
regions is common, with 12 objects being identified in 5
ULIRGs. These regions show a large range of dynamical mass
up to
, with average
sizes of ~750 pc. In addition, the line ratios (H ii
region-like), metallicities (
) and Hα equivalent widths (34–257 Å) are typical of young bursts of star formation (age ∼ 5–8 Myr), and similar to those of the TDG candidates found in less
luminous mergers and compact groups of galaxies. The extinction corrected
Hα luminosity of these young bursts leads to masses for the
young stellar component of ~
–
.
The likelihood of survival of these regions as TDGs is
discussed based on their
structural and kinematic properties. Particularly interesting
is our finding that most of these systems
follow the relation between effective radius and velocity dispersion found
at lower (globular clusters) and higher (Elliptical) mass
systems, which suggests they are stable against internal
motions.
The stability against forces from the parent galaxy is
studied on the basis of several criteria and a comparison of
the data with the predictions of dynamical evolutionary models is
also performed. Five regions out of twelve show
High-Medium or High likelihood of survival
based on all the utilised tracers.
Our best candidate, which satisfies all criteria,
is located in the advanced merger
IRAS 15250+3609 and presents a velocity field decoupled from the
relatively distant parent galaxy.
Key words: galaxies: active / galaxies: interactions / galaxies: starburst / galaxies: dwarf
© ESO, 2007
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