ISO observations of the Wolf-Rayet galaxies NGC 5430, NGC 6764, Mrk 309 and VII Zw 19

¹ Dunsink Observatory, Castleknock, Dublin 15, Ireland e-mail: boh@physics.gmu.edu
² Dept. of Physics and Astronomy, George Mason University, Fairfax, Virginia, 22030, USA
³ Physics Department, University College, Belfield, Dublin 4, Ireland
⁴ XMM-Newton Science Operations Centre, European Space Agency, Villafranca del Castillo, PO Box 50727, 28080 Madrid, Spain

Received: 19 July 2004
Accepted: 10 May 2005

Abstract

Observations of four WR galaxies (NGC 5430, NGC 6764, Mrk 309 and VII Zw 19) using the Infrared Space Observatory are presented here. ISOCAM maps of NGC 5430, Mrk 309 and NGC 6764 revealed the location of star formation regions in each of these galaxies. ISOPHOT spectral observations from 4 to 12 μm detected the ubiquitous PAH bands in the nuclei of the targets and several of the disk star forming regions, while LWS spectroscopy detected [O I] and [C II] emission lines from two galaxies, NGC 5430 and NGC 6764.
Using a combination of ISO and IRAS flux densities, a dust model based on the sum of modified blackbody components was successfully fitted to the available data. These models were then used to calculate new values for the total IR luminosities for each galaxy, the size of the various dust populations, and the global SFR.
The derived flux ratios, the SFRs, the high L(PAH)/L(40–120 μm) and F(PAH 7.7 μm)/F(7.7 μm continuum) values suggest that most of these galaxies are home to only a compact burst of star formation. The exception is NGC 6764, whose F(PAH 7.7 μm)/F(7.7 μm continuum) value of 1.22 is consistent with the presence of an AGN, yet the L(PAH)/L(40–120 μm) is more in line with a starburst, a finding in line with a compact low-luminosity AGN dominated by the starburst.