2001A&A...378...51B


Query : 2001A&A...378...51B

2001A&A...378...51B - Astronomy and Astrophysics, volume 378, 51-69 (2001/10-4)

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

BRAINE J., DUC P.-A., LISENFELD U., CHARMANDARIS V., VALLEJO O., LEON S. and BRINKS E.

Abstract (from CDS):

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 108M. 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.

Abstract Copyright:

Journal keyword(s): stars: formation - galaxies: evolution - galaxies: formation - galaxies: interactions - galaxies: ISM - cosmology: dark matter

Nomenclature: Table 1: [BDL2001] NGC NNNNW N=7, [BDL2001] IC 1182E N=1.

CDS comments: in ref list Combes, Dupraz 1988A&A...203L...9C instead of 203.9. Table 2: Arp 105S = [BLD2000] A105S, Arp 245N = [BLD2000] A245N.

Simbad objects: 46

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Number of rows : 46
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 UGC 12914 LIN 00 01 38.3220061296 +23 29 01.190922432   13.2       ~ 142 1
2 UGC 12915 GiP 00 01 41.937 +23 29 45.20   13.9       ~ 114 1
3 IC 10 G 00 20 23.16 +59 17 34.7   13.6 9.5     ~ 1060 0
4 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10194 1
5 UGC 957 GiC 01 24 24.46 +03 52 55.0   18       ~ 38 2
6 NGC 520 IG 01 24 35.071 +03 47 32.68 12.41 12.24 11.42     ~ 503 3
7 NGC 660 Sy2 01 43 02.350 +13 38 44.45   12.02 11.16     ~ 537 2
8 NGC 1569 IG 04 30 49.186 +64 50 52.52 11.72 11.86 11.03     ~ 1196 3
9 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15990 1
10 UGC 4483 GiG 08 37 03.29 +69 46 29.2 15.70 15.46 14.98 14.89   ~ 282 0
11 [BDL2001] NGC 2782W GiG 09 13 48.5 +40 10 11           ~ 1 0
12 NGC 2782 Sy2 09 14 05.120 +40 06 49.68 12.29 12.30 11.63     ~ 447 3
13 NGC 2992 Sy2 09 45 42.045 -14 19 34.90 13.54 13.14 12.18 12.6 12.2 ~ 828 3
14 [BLD2000] A245N G 09 45 44.1 -14 17 28           ~ 8 2
15 NGC 2993 EmG 09 45 48.325 -14 22 06.02 12.72 13.11 12.64 13.4 13.0 ~ 170 1
16 M 81 Sy2 09 55 33.1726556496 +69 03 55.062505368   7.89 6.94     ~ 4168 3
17 NGC 3077 GiP 10 03 19.0965510921 +68 44 01.556166166 11.23 10.85 10.14 9.74   ~ 724 0
18 NAME Sex A H2G 10 11 00.5 -04 41 30 12.48 12.13 11.93 11.78   ~ 690 2
19 NGC 3561 LIN 11 11 13.1887412400 +28 41 47.044176900   14.7       ~ 185 2
20 [BLD2000] A105S G 11 11 13.5 +28 41 20           ~ 10 2
21 [BDL2001] NGC 4038S GiG 12 01 25.6 -19 00 34           ~ 1 0
22 NGC 4038 GiP 12 01 53.002 -18 52 03.32   10.91   9.74 11.0 ~ 1296 1
23 NAME Antennae IG 12 01 53.170 -18 52 37.92           ~ 1617 0
24 NGC 4039 GiP 12 01 53.8 -18 53 06   11.08   9.77   ~ 1145 1
25 NGC 4228 SBG 12 15 39.174 +36 19 36.80 10.63 10.30 9.93 9.74   ~ 912 1
26 Mrk 209 bCG 12 26 16.02 +48 29 36.6   15.3       ~ 320 0
27 NGC 4435 GiG 12 27 40.503 +13 04 44.48 12.23 11.74 10.80     ~ 426 2
28 NGC 4438 LIN 12 27 45.6705493536 +13 00 31.708096380 11.37 11.02 10.17     ~ 608 2
29 NGC 4449 EmG 12 28 11.118 +44 05 36.81 10.11 9.98 9.64 9.45   ~ 1071 1
30 IC 819 AGN 12 46 10.060 +30 43 54.64           ~ 263 1
31 NGC 4676 IG 12 46 10.18 +30 43 53.7   14.1       ~ 303 0
32 [BDL2001] NGC 4676N GiG 12 46 10.5 +30 45 37           ~ 1 0
33 NAME Centaurus A Sy2 13 25 27.6039817176 -43 01 09.493008456   8.18 6.84 6.66   ~ 4230 3
34 LEDA 718304 GiG 13 47 20.5 -30 20 54   18.27 17.91     ~ 25 0
35 [BDL2001] NGC 5291S GiG 13 47 23.0 -30 27 30           ~ 12 0
36 NGC 5291 AGN 13 47 24.5000261808 -30 24 25.449445800   15.18 14.00 13.57 12.7 ~ 145 1
37 UGC 9128 G 14 15 56.70 +23 03 16.2 15.40 14.77 14.41 14.32   ~ 268 0
38 IC 1182 AGN 16 05 36.7963581312 +17 48 07.422094440   16.20 15.19     ~ 156 0
39 SDSS J160541.92+174758.3 GiG 16 05 41.92320 +17 47 58.3368           ~ 7 0
40 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1496 0
41 NAME Aquarius Dwarf G 20 46 51.7 -12 50 54 15.75 15.18 14.83 14.46   ~ 417 1
42 [BDL2001] NGC 7252W GiG 22 20 33.6 -24 37 24           ~ 2 0
43 NGC 7252 IG 22 20 44.7748209648 -24 40 41.909518200 12.26 12.46 12.06 11.57   ~ 683 1
44 NAME Stephan's Quintet CGG 22 35 57.5 +33 57 36           ~ 396 1
45 NGC 7319 Sy2 22 36 03.602 +33 58 33.18   14.57 13.53 12.65   ~ 266 0
46 [BDL2001] NGC 7319E GiG 22 36 10.3 +33 57 17           ~ 1 0

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2022.05.21-11:48:36

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