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

TL;DR

This study characterizes the massive star population in the nearby dwarf irregular galaxy IC 4662, revealing Wolf-Rayet stars, embedded ionizing sources, and star formation properties in comparison with other metal-poor galaxies.

Contribution

It provides the first spatially resolved identification of Wolf-Rayet stars and embedded ionizing sources in IC 4662, and assesses its starburst status based on star formation surface density.

Findings

Wolf-Rayet stars are associated with multiple sources and clusters in IC 4662.

A significant fraction (30-50%) of ionizing photons are deeply embedded within HII regions.

IC 4662's star formation surface density varies with the scale length used, affecting its classification as a starburst galaxy.

Abstract

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, 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 HII 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 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 Halpha-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, R_25. If instead, we were to adopt the V-band scale length R_D from Hunter & Elmegreen, IC 4662 would comfortably qualify as a starburst galaxy, since its star formation intensity would exceed 0.1 M_sun/yr/kpc^2.