Massive star formation in Wolf-Rayet galaxies

V. Star-formation rates, masses and the importance of galaxy interactions

¹ CSIRO Astronomy and Space Science / Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia e-mail: Angel.Lopez-Sanchez@csiro.au
² Instituto de Astrofísica de Canarias, C/ Vía Láctea S/N, 38200 La Laguna, Tenerife, Spain

Received: 20 February 2010
Accepted: 3 May 2010

Abstract

Aims. We performed a comprehensive analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars, most of them classified as Wolf-Rayet galaxies.

Methods. In this paper, the last in the series, we analyze the global properties of our galaxy sample using multiwavelength data extracted from our own observations (Hα fluxes, B and H-band magnitudes) and from the literature, which include X-ray, FUV, FIR, and radio (both H i spectral line and 1.4 GHz radio-continuum) measurements.

Results. The agreement between our Hα-based star-formation rates (Sfr) and those provided by indicators at other wavelengths is remarkable, but we consider that the new Hα-based calibration provided by Calzetti et al. (2007, ApJ, 666, 870) should be preferred to older calibrations. The FUV-based Sfr provides a powerful tool for analyzing the star-formation activity on both global and local scales independently to the Hα emission. We provide empirical relationships between the ionized gas mass, neutral gas mass, dust mass, stellar mass, and dynamical mass with the B-luminosity. Although all mass estimations increase with increasing luminosity, we find important deviations to the general trend in some objects, which seem to be the consequence of their particular evolutionary histories. The analysis of the mass-to-light ratios give similar results. We investigate the mass-metallicity relations and conclude that both the nature and the star-formation history are needed to understand the relationships between both properties. The majority of the galaxies follow a Schmidt-Kennicutt scaling law of star-formation that agrees with that reported in individual star-forming regions within M 51 but not with that found in normal spiral galaxies. Dwarf galaxies seem to be forming stars more efficiently than the outskirts of spiral galaxies. We find a relation between the reddening coefficient and the warm dust mass indicating that the extinction is mainly internal to the galaxies. The comparison with the closed-box model also indicates that the environment has strongly affected their evolution.

Conclusions. Considering all multiwavelength data, we found that 17 up to 20 galaxies are clearly interacting or merging with low-luminosity dwarf objects or H i clouds. The remaining three galaxies (Mkn 5, SBS 1054+364, and SBS 1415+437) show considerable divergences of some properties when comparing with similar objects. Many of the interacting/merging features are only detected when deep optical spectroscopy and a detailed multiwavelength analysis, including H i observations, are obtained. We conclude that interactions do play a fundamental role in the triggering mechanism of the strong star-formation activity observed in dwarf starburst galaxies.