Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” 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 “missing baryons,” 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, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” 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 “dark matter”. 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 – 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.
References
[1]
P.-A. Duc, E. Brinks, V. Springel, B. Pichardo, P. Weilbacher, and I. F. Mirabel, “Formation of a tidal dwarf galaxy in the interacting system ARP 245 (NGC 2992/93),” The Astronomical Journal, vol. 120, no. 3, pp. 1238–1264, 2000.
[2]
F. Zwicky, “Multiple galaxies,” in Ergebnisse der Exakten Naturwissenschaften, vol. 29, pp. 344–385, 1956.
[3]
F. Schweizer, “Galaxies with long tails,” in Structure and Properties of Nearby Galaxies, E. M. Berkhuijsen and R. Wielebinski, Eds., vol. 77 of IAU Symposium Series, pp. 279–284, 1978.
[4]
I. F. Mirabel, H. Dottori, and D. Lutz, “Genesis of a dwarf galaxy from the debris of the antennae,” Astronomy & Astrophysics, vol. 256, pp. L19–L22, 1992.
[5]
P. M. Weilbacher, U. Fritze-v. Alvensleben, P.-A. Duc, and K. J. Fricke, “Large velocity gradients in the tidal tails of the interacting galaxy AM 1353-272 (“the dentist's chair”),” The Astrophysical Journal, vol. 579, pp. L79–L82, 2002.
[6]
A. Toomre, “Mergers and some consequences,” in Evolution of Galaxies and Stellar Populations, B. M. Tinsley and R. B. Larson, Eds., vol. 197, p. 401, Yale University Observatory, New Haven, Conn, USA, 1977.
[7]
P. di Matteo, F. Bournaud, M. Martig, F. Combes, A.-L. Melchior, and B. Semelin, “On the frequency, intensity, and duration of starburst episodes triggered by galaxy interactions and mergers,” Astronomy & Astrophysics, vol. 492, no. 1, pp. 31–49, 2008.
[8]
C. Struck, M. Kaufman, E. Brinks, M. Thomasson, B. G. Elmegreen, and D. M. Elmegreen, “The grazing encounter between IC 2163 and NGC 2207: pushing the limits of observational modelling,” Monthly Notices of the Royal Astronomical Society, vol. 364, no. 1, pp. 69–90, 2005.
[9]
B. J. Smith, C. Struck, M. Hancock, et al., “Stochastic “beads on a string” in the accretion tail of ARP 285,” The Astronomical Journal, vol. 135, no. 6, pp. 2406–2423, 2008.
[10]
M. Wetzstein, T. Naab, and A. Burkert, “Do dwarf galaxies form in tidal tails?” Monthly Notices of the Royal Astronomical Society, vol. 375, no. 3, pp. 805–820, 2007.
[11]
F. Bournaud and P.-A. Duc, “From tidal dwarf galaxies to satellite galaxies,” Astronomy & Astrophysics, vol. 456, no. 2, pp. 481–492, 2006.
[12]
F. Bournaud, P.-A. Duc, P. Amram, F. Combes, and J.-L. Gach, “Kinematics of tidal tails in interacting galaxies: tidal dwarf galaxies and projection effects,” Astronomy & Astrophysics, vol. 425, no. 3, pp. 813–823, 2004.
[13]
B. G. Elmegreen, M. Kaufman, and M. Thomasson, “An interaction model for the formation of dwarf galaxies and 10 exp 8 solar mass clouds in spiral disks,” The Astrophysical Journal, vol. 412, no. 1, pp. 90–98, 1993.
[14]
P.-A. Duc, F. Bournaud, and F. Masset, “A top-down scenario for the formation of massive tidal dwarf galaxies,” Astronomy & Astrophysics, vol. 427, no. 3, pp. 803–814, 2004.
[15]
F. Bournaud, P.-A. Duc, and F. Masset, “The large extent of dark matter haloes probed by the formation of tidal dwarf galaxies,” Astronomy & Astrophysics, vol. 411, no. 2, pp. L469–L472, 2003.
[16]
F. Bournaud and F. Combes, “Formation of polar ring galaxies,” Astronomy & Astrophysics, vol. 401, no. 3, pp. 817–833, 2003.
[17]
B. Koribalski and J. M. Dickey, “Neutral hydrogen gas in interacting galaxies: the NGC 6221/6215 galaxy group,” Monthly Notices of the Royal Astronomical Society, vol. 348, no. 4, pp. 1255–1274, 2004.
[18]
M. Hancock, B. J. Smith, C. Struck, M. L. Giroux, and S. Hurlock, “Candidate tidal dwarf galaxies in arp 305: lessons on dwarf detachment and globular cluster formation,” The Astrophysical Journal, vol. 137, pp. 4643–4654, 2009.
[19]
K. A. Knierman, S. C. Gallagher, J. C. Charlton, et al., “From globular clusters to tidal dwarfs: structure formation in the tidal tails of merging galaxies,” The Astronomical Journal, vol. 126, pp. 1227–1244, 2003.
[20]
J. F. Navarro, C. S. Frenk, and S. D. M. White, “The structure of cold dark matter halos,” The Astrophysical Journal, vol. 462, no. 2, pp. 563–575, 1996.
[21]
J. S. Bullock, A. V. Kravtsov, and P. Colín, “Angular momentum profiles of warm dark matter halos,” The Astrophysical Journal, vol. 564, pp. L1–L4, 2002.
[22]
F. Bournaud, P.-A. Duc, E. Brinks, et al., “Missing mass in collisional debris from galaxies,” Science, vol. 316, no. 5828, pp. 1166–1169, 2007.
[23]
J. Braine, P.-A. Duc, U. Lisenfeld, et al., “Abundant molecular gas in tidal dwarf galaxies: on-going galaxy formation,” Astronomy & Astrophysics, vol. 378, no. 1, pp. 51–69, 2001.
[24]
M. Boquien, P.-A. Duc, J. Braine, E. Brinks, U. Lisenfeld, and V. Charmandaris, “Polychromatic view of intergalactic star formation in NGC 5291,” Astronomy & Astrophysics, vol. 467, no. 1, pp. 93–106, 2007.
[25]
D. Pfenniger, F. Combes, and L. Martinet, “Is dark matter in spiral galaxies cold gas? I. Observational constraints and dynamical clues about galaxy evolution,” Astronomy & Astrophysics, vol. 285, pp. 79–93, 1994.
[26]
D. Pfenniger and F. Combes, “Is dark matter in spiral galaxies cold gas? II. Fractal models and star non-formation,” Astronomy & Astrophysics, vol. 285, pp. 94–118, 1994.
[27]
D. Pfenniger, S. D. Ryder, D. J. Pisano, M. A. Walker, and K. C. Freeman, Eds., vol. 220 of IAU Symposium Series, p. 241, 2004.
[28]
P. M. W. Kalberla, L. Dedes, J. Kerp, and U. Haud, “Dark matter in the Milky Way II. The HI gas distribution as a tracer of the gravitational potential,” Astronomy and Astrophysics, vol. 469, no. 2, pp. 511–527, 2007.
[29]
Y. Revaz, D. Pfenniger, F. Combes, and F. Bournaud, “Simulations of galactic disks including a dark baryonic component,” Astronomy & Astrophysics, vol. 501, no. 1, pp. 171–187, 2009.
[30]
G. Gentile, B. Famaey, F. Combes, P. Kroupa, H. S. Zhao, and O. Tiret, “Tidal dwarf galaxies as a test of fundamental physics,” Astronomy & Astrophysics, vol. 472, no. 2, pp. L25–L28, 2007.
[31]
M. Milgrom, “MOND and the mass discrepancies in tidal dwarf galaxies,” The Astrophysical Journal, vol. 667, p. L45, 2007.
[32]
J. I. Read, G. Lake, O. Agertz, and V. P. Debattista, “Thin, thick and dark discs in cDM,” Monthly Notices of the Royal Astronomical Society, vol. 389, no. 3, pp. 1041–1057, 2008.
[33]
C. W. Purcell, J. S. Bullock, and M. Kaplinghat, “The dark disk of the milky way,” submitted to The Astrophysical Journal.
[34]
I. Saviane, Y. Momany, G. S. da Costa, R. M. Rich, and J. E. Hibbard, “A new red giant-based distance modulus of 13.3 Mpc to the antennae galaxies and its consequences,” The Astrophysical Journal, vol. 678, no. 1, pp. 179–186, 2008.
[35]
F. Schweizer, C. R. Burns, B. F. Madore, et al., “A new distance to the antennae galaxies (NGC 4038/39) based on the type ia supernova 2007,” The Astronomical Journal, vol. 136, no. 4, pp. 1482–1489, 2008.
[36]
P.-A. Duc, J. Braine, T. J. Lisenfeld, E. Brinks, and M. Boquien, “VCC 2062: an old tidal dwarf galaxy in the Virgo cluster?” Astronomy & Astrophysics, vol. 475, no. 1, pp. 187–197, 2007.
[37]
T. Okazaki and Y. Taniguchi, “Dwarf galaxy formation induced by galaxy interactions,” The Astrophysical Journal, vol. 543, no. 1, pp. 149–152, 2000.
[38]
M. Martig, F. Bournaud, R. Teyssier, and A. Dekel, “Morphological quenching of star formation: making early-type galaxies red,” submitted to The Astrophysical Journal.
[39]
S. Recchi, C. Theis, P. Kroupa, and G. Hensler, “The early evolution of tidal dwarf galaxies,” Astronomy & Astrophysics, vol. 470, no. 1, pp. L5–L8, 2007.
[40]
F. Bournaud, P.-A. Duc, and E. Emsellem, “High-resolution simulations of galaxy mergers: resolving globular cluster formation,” Monthly Notices of the Royal Astronomical Society, vol. 389, no. 1, pp. L8–L12, 2008.
[41]
D. M. Elmegreen, B. G. Elmegreen, T. Ferguson, and B. Mullan, “Smooth and starburst tidal tails in the GEMS and GOODS fields,” The Astrophysical Journal, vol. 663, pp. 734–751, 2007.
[42]
L. Michel-Dansac, D. G. Lambas, M. S. Alonso, and P. Tissera, “The mass—metallicity relation of interacting galaxies,” Monthly Notices of the Royal Astronomical Society, vol. 386, no. 1, pp. L82–L86, 2008.
