EDP Sciences
Free access
Volume 499, Number 2, May IV 2009
Page(s) 455 - 464
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361/200911758
Published online 19 March 2009
A&A 499, 455-464 (2009)
DOI: 10.1051/0004-6361/200911758

On the massive star content of the nearby dwarf irregular Wolf-Rayet galaxy IC 4662

P. A. Crowther and J. L. Bibby

Department of Physics & Astronomy, Hicks Building, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK
    e-mail: Paul.Crowther@sheffield.ac.uk

Received 30 January 2009 / Accepted 11 March 2009

Aims. We investigate the massive stellar content of the nearby dwarf irregular Wolf-Rayet galaxy IC 4662, and consider its global star forming properties in the context of other metal-poor galaxies, namely the SMC, IC 10 and NGC 1569.
Methods. Very Large Telescope/FORS2 imaging and spectroscopy plus archival Hubble Space Telescope/ACS imaging datasets permit us to spatially identify the location, number and probable subtypes of Wolf-Rayet stars within this galaxy. We also investigate suggestions that a significant fraction of the ionizing photons of the two giant H II regions A1 and A2 lie deeply embedded within these regions.
Results. Wolf-Rayet stars are associated with a number of sources within IC 4662-A1 and A2, plus a third compact H II region to the north west of A1 (A1-NW). Several sources appear to be isolated, single (or binary) luminous nitrogen sequence WR stars, while extended sources are clusters whose masses exceed the Orion Nebula Cluster by, at most, a factor of two. IC 4662 lacks optically visible young massive, compact clusters that are common in other nearby dwarf irregular galaxies. A comparison between radio and H$\alpha$-derived ionizing fluxes of A1 and A2 suggests that 30–50% of their total Lyman continuum fluxes lie deeply embedded within these regions.
Conclusions. The star formation surface density of IC 4662 is insufficient for this galaxy to qualify as a starburst galaxy, based upon its photometric radius, R25. If instead, we were to adopt the V-band scale length $R_{\rm D}$ from Hunter & Elmegreen, IC 4662 would comfortably qualify as a starburst galaxy, since its star formation intensity would exceed 0.1 $M_{\odot}$ yr-1 kpc-2.

Key words: galaxies: individual: IC 4662 -- stars: Wolf-Rayet -- ISM: HII regions -- galaxies: star clusters -- galaxies: starburst -- galaxies: dwarf

© ESO 2009