Hα imaging survey of Wolf–Rayet galaxies: morphologies and star formation rates

Abstract

The Halpha and optical broadband images of 25 nearby Wolf-Rayet (WR) galaxies are presented. The WR galaxies are known to have the presence of a recent ($\le$10 Myr) and massive star formation episode. The photometric Halpha fluxes are estimated, and corrected for extinction and line contamination in the filter pass-bands. The star formation rates (SFRs) are estimated using Halpha images and from the archival data in the far-ultraviolet (FUV), far-infrared (FIR) and 1.4 GHz radio continuum wave-bands. A comparison of SFRs estimated from different wavebands is made after including similar data available in literature for other WR galaxies. The Halpha based SFRs are found to be tightly correlated with SFRs estimated from the FUV data. The correlations also exist with SFRs estimates based on the radio and FIR data. The WR galaxies also follow the radio-FIR correlation known for normal star forming galaxies, although it is seen here that majority of dwarf WR galaxies have radio deficiency. An analysis using ratio of non-thermal to thermal radio continuum and ratio of FUV to Halpha SFR indicates that WR galaxies have lesser non-thermal radio emission compared to normal galaxies, most likely due to lack of supernova from the very young star formation episode in the WR galaxies. The morphologies of 16 galaxies in our sample are highly suggestive of an ongoing tidal interaction or a past merger in these galaxies. This survey strengthens the conclusions obtained from previous similar studies indicating the importance of tidal interactions in triggering star-formation in WR galaxies.