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Interactions and star formation activity in Wolf-Rayet galaxies
ґ Angel R. Lґ ez-Sґ hez1 and Cґ op anc esar Esteban
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CSIRO ATNF, Australia Angel.Lopez-Sanchez@csiro.au Instituto de Astrofґ isica de Canarias, Spain, cel@iac.es

We present some global results of the PhD Thesis carried out by Lґ ezop Sґ hez (2006), in which a detailed morphological, photometrical and spectrosanc copical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was realized. The main aims are the study of the star formation and O and WR stellar populations in these galaxies and the role that interactions between low surface companion ob jects have in the triggering of the bursts. We analyze the morphology, stellar populations, physical conditions, chemical abundances and kinematics of the ionized gas, and star-formation activity of each system.

1 Intro duction
WR galaxies are a subtype of H ii galaxies whose integrated spectra show broad emission lines attributed to WR stars, indicating the presence of an important population of massive stars and the youth of the burst. Studying a sample of WR galaxies, [3] and [4] suggested that interactions with or between dwarf ob jects could be the main star formation triggering mechanism in dwarf galaxies and noted that the nature of WR galaxies can be only detected when deep and high-resolution images and spectra are available. Subsequent works also found a relation between massive star formation and the presence of interaction signatures. Thus, we have performed a detailed analysis of a sample of 20 WR galaxies combining deep optical and near-infrared (NIR) broad band and H imaging together with optical spectroscopy (long slit and echelle) data. Additional X-ray, far-infrared and radio data were compiled from literature.

2 Global prop erties
The global analysis of our sample of 20 Wolf-Rayet galaxies is the more complete and exhaustive data set of this kind of galaxies, involving multiwavelength results and being every system analyzed following the same procedures (see [5] and references within). Our main global results are:


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ґ Angel R. Lґ ez-Sґ hez and Cґ op anc esar Esteban

1. The analysis of WR features in our sample suggests that aperture effects and localization of the bursts with WR stars seem to play a fundamental role in the detection of this sort of massive stars in starburst galaxies. 2. Photometric data have been corrected for both extinction and nebular emission using our spectroscopic values. A good agreement between our optical and NIR colors and theoretical models is found; small discrepancies are explained by the existence of several stellar populations. 3. Physical and chemical properties are in agreement with both previous observations and models of chemical evolution of galaxies. We have compared abundances obtained by the direct method with those obtained for several empirical calibrations: [6, 7] seems to give similar results whereas calibrations based in photoionization models such as [2] and [1] give abundances higher (0.20 dex) than expected. 4. The comparison of the SFR derived from our H data (corrected by both extinction and [N ii] emission using our spectroscopic data) is in good agreement with the SFR obtained using multiwavelength relations. We have also derived an X-ray based SFR for this kind of starburst galaxies. 5. We have determine the ionized gas mass (MH II ), neutral gas mass (MH I ), mass of the ionizing stellar cluster (M ), warm dust mass (Mdust ), Keplerian mass (Mkep ) and the dynamical mass (Mdyn ). As it expected, all mass values increase with the luminosity of the galaxy. Furthermore, we find a good correlation between Mdyn and the luminosity of the galaxy, as well as a clear relation between the reddening coefficient derived from the Balmer decrement, C (H ), and Mdust . This fact suggests that extinction is mainly produced within the starburst. 6. However, our main conclusion is that the ma jority of studied galaxies (16 up to 20, 80% of the ob jects) show clear interaction features such as plumes, tails, tidal dwarf galaxies (TDGs), regions with very different chemical abundances inside galaxies, perturbed kinematics of the ionized gas or lack of neutral hydrogen gas, confirming the hyp othesis that interaction with or b etween dwarf ob jects triggers the star formation activity in Wolf-Rayet galaxies.

References
1. Kewley, L.J. & Dopita, M.A. 2002, ApJS, 142, 35 2. McGaugh, S.S. 1994, ApJ, 426, 135 3. Mґ endez, D.I. 1999, Gas ionizado y formaciґ estelar en galaxias Wolf-Rayet, on PhD Thesis, La Laguna University, Tenerife, Spain 4. Mґ endez, D.I. & Esteban, C., 2000, A&A, 359, 493 ґ 5. Lґ ez-Sґ hez, A.R. 2006, Massive star formation in dwarf Wolf-Rayet op anc galaxies. PhD Thesis, La Laguna University, Tenerife, Spain, see astroph/0704.2846 for a 16 pages English resume with figures. 6. Pilyugin, L.S. 2001b, A&A, 369, 594 7. Pilyugin, L.S. 2001b, A&A, 374, 412