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

Abstract

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. 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 Hii regions A1 and A2 lie deeply embedded within these regions. Wolf-Rayet stars are associated with a number of sources within IC 4662-A1 and A2, plus a third compact HII 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 Hα-derived ionizing fluxes of A1 and A2 suggests that 30–50% of their total Lyman continuum fluxes lie deeply embedded within these regions. 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 RD from Hunter & Elmegreen, IC 4662 would comfortably qualify as a starburst galaxy, since its star formation intensity would exceed 0.1 Mpc yr−1kpc−2.