Revealing the Young Starburst in Haro 3 with Radio and Infrared Imaging

Abstract

The Wolf-Rayet galaxy Haro 3 (Mrk 35, NGC 3353) was observed at the near-IR and radio wavelengths as part of ongoing program to study the earliest stages of starbursts. These observations confirm that the current episode of star formation is dominated by a single region (region A). While there are knots of recent (~10 Myr) star formation outside of region A, the sources of ionizing radiation as observed in both radio and Br-gamma observations are almost exclusively associated with region A. The derived ionizing flux implies a star formation rate of ~0.6 solar masses per year localized within a radius of ~0.1 kpc. A comparison with observations from HST indicates that one or more of the star clusters in region A are optically obscured. The star clusters in region A have ages at least as young as ~5 Myr, and possibly as young as ~0.1 Myr. The star cluster that appears to be the youngest also exhibits a near-IR excess in its colors, possibly indicating natal dust in very close proximity to the ionizing stars. The difference between optical- and radio-determined ionizing fluxes as well as the near-IR colors indicate an average extinction value of A_V ~2.5 in region A. The total stellar mass associated with the current starburst in region A is inferred from both the near-IR and radio observations to be ~10^6 solar masses. The other main stellar concentrations observed in the near-IR (Regions B1 and B2) are somewhat older than region A, with ages ~8-10 Myr, and the near-IR observations indicate they have stellar masses of ~8x10^4 and ~2x10^4 solar masses, respectively.