Optical and NIR Investigation of a Sample of Tidal Dwarf Candidates

Weilbacher, Peter M.; Alvensleben, U. Fritze-von; Duc, Pierre–Alain

doi:10.1007/978-94-017-3315-1_68

Cited by 15 publications

(27 citation statements)

References 10 publications

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“…In this way, the structures formed are expected to be made up of an older disk population and a younger burst population that forms from the condensing gas. Evidence for this scenario has been given by Weilbacher et al (2000Weilbacher et al ( , 2004, who find that the colours of Tidal Dwarf Galaxy candidates can be well fit Table 1. Specific U-band luminosity for the different regions of NGC 6872 and the implied star formation rates using the Larsen & Richtler (2000) relation.…”

Section: Cluster Formationmentioning

confidence: 83%

“…As the Tidal Dwarf Galaxy candidates also presumably form in the tidal tails (Duc & Mirabel 1998;Weilbacher et al 2000), it is tempting to consider a common formation mechanism, although this is not necessarily the case. Optical and near-infrared spectroscopy/photometry will be necessary to determine if there is a significant underlying old stellar population within the young clusters presented here (e.g.…”

Section: Cluster Formationmentioning

confidence: 99%

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The star cluster population in the tidal tails of NGC 6872

Bastian

Hempel

Kissler-Patig

et al. 2005

A&A

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Abstract. We present a photometric analysis of the rich star cluster population in the tidal tails of NGC 6872. We find star clusters with ages between 1−100 Myr distributed in the tidal tails, while the tails themselves have an age of less than 150 Myr. Most of the young massive (10 4 ≤ M/M ≤ 10 7 ) clusters are found in the outer regions of the galactic disk or the tidal tails. The mass distribution of the cluster population can be well described by a power-law of the form N(m) ∝ m −α , where α = 1.85 ± 0.11, in very good agreement with other young cluster populations found in a variety of different environments. We estimate the star formation rate for three separate regions of the galaxy, and find that the eastern tail is forming stars at ∼2 times the rate of the western tail and ∼5 times the rate of the main body of the galaxy. By comparing our observations with published N-body models of the fate of material in tidal tails in a galaxy cluster potential, we see that many of these young clusters will be lost into the intergalactic medium. We speculate that this mechanism may also be at work in larger galaxy clusters such as Fornax, and suggest that the so-called ultra-compact dwarf galaxies could be the most massive star clusters that have formed in the tidal tails of an ancient galactic merger.

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Section: Cluster Formationmentioning

confidence: 83%

Section: Cluster Formationmentioning

confidence: 99%

The star cluster population in the tidal tails of NGC 6872

Bastian

Hempel

Kissler-Patig

et al. 2005

A&A

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“…3.1 also seem to contain a strong old stellar component (Weilbacher et al 2000). They are therefore most likely preexistent companion galaxies, which are either projected onto the tidal features or falling into the interacting system.…”

Section: Metallicitiesmentioning

confidence: 94%

Tidal dwarf candidates in a sample of interacting galaxies

Weilbacher¹,

Duc²,

Alvensleben³

2002

A&A

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Abstract. We present low-resolution spectroscopy of the ionized gas in a sample of optical knots located along the tidal features of 14 interacting galaxies previously selected as candidate Tidal Dwarf Galaxies (TDGs). From redshift measurements, we are able to confirm their physical association with the interacting system in almost all cases. For most knots, the oxygen abundance does not depend on the blue luminosity. The average, 12 + log(O/H) = 8.34 ± 0.20, is typical of TDGs and is comparable to that measured in the outer stellar disk of spirals from which they were formed. A few knots showing low metallicities are probably pre-existing low-mass companions. The estimated Hα luminosity of the TDG candidates is higher than that of typical individual H  regions in spiral disks and is comparable to the global Hα luminosity of dwarf galaxies. We find several instances of velocity gradients with amplitudes apparently larger than 100 km s −1 in the ionized gas in the tidal knots and discuss various possible origins for the large velocity amplitudes. While we can exclude tidal streaming motions and outflows, we cannot rule out projection effects with the current resolution. The velocity gradients could be indicative of the internal kinematic characteristic of self-gravitating objects. Higher resolution spectra are required to confirm whether the tidal knots in our sample have already acquired their dynamical independence and are therefore genuine Tidal Dwarf Galaxies.

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“…TDGs, and dwarf galaxies in general, contain lots of gas, a highly varying amount of star formation, and usually an older stellar component (Weilbacher et al 2000). They are found at the ends of tidal tails which can reach 100 kpc from the nuclei of the parent galaxies.…”

Section: Introductionmentioning

confidence: 99%

Abundant molecular gas in tidal dwarf galaxies: On-going galaxy formation

Braine

Duc

Lisenfeld

et al. 2001

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Abstract. We investigate the process of galaxy formation as can be observed in the only currently forming galaxies -the so-called Tidal Dwarf Galaxies, hereafter TDGs -through observations of the molecular gas detected via its CO (Carbon Monoxide) emission. These objects are formed of material torn off of the outer parts of a spiral disk due to tidal forces in a collision between two massive galaxies. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of gas and a bona fide galaxy. We have detected CO in 8 TDGs (two of them have already been published in Braine et al. 2000, hereafter Paper I), with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 10 8 M . The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular gas masses is observed, in accord with the transformation of HI into H2. Although TDGs share many of the properties of small irregulars, their CO luminosity is much greater (factor ∼100) than that of standard dwarf galaxies of comparable luminosity. This is most likely a consequence of the higher metallicity (&1/3 solar) of TDGs which makes CO a good tracer of molecular gas. This allows us to study star formation in environments ordinarily inaccessible due to the extreme difficulty of measuring the molecular gas mass. The star formation efficiency, measured by the CO luminosity per Hα flux, is the same in TDGs and full-sized spirals. CO is likely the best tracer of the dynamics of these objects because some fraction of the HI near the TDGs may be part of the tidal tail and not bound to the TDG. Although uncertainties are large for individual objects, as the geometry is unknown, our sample is now of eight detected objects and we find that the "dynamical" masses of TDGs, estimated from the CO line widths, seem not to be greater than the "visible" masses (HI + H2 + a stellar component). Although higher spatial resolution CO (and HI) observations would help reduce the uncertainties, we find that TDGs require no dark matter, which would make them the only galaxy-sized systems where this is the case. Dark matter in spirals should then be in a halo and not a rotating disk. Most dwarf galaxies are dark matter-rich, implying that they are not of tidal origin. We provide strong evidence that TDGs are self-gravitating entities, implying that we are witnessing the ensemble of processes in galaxy formation: concentration of large amounts of gas in a bound object, condensation of the gas, which is atomic at this point, to form molecular gas and the subsequent star formation from the dense molecular component.

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Optical and NIR Investigation of a Sample of Tidal Dwarf Candidates

Cited by 15 publications

References 10 publications

The star cluster population in the tidal tails of NGC 6872

The star cluster population in the tidal tails of NGC 6872

Tidal dwarf candidates in a sample of interacting galaxies

Abundant molecular gas in tidal dwarf galaxies: On-going galaxy formation

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