Central free-free dominated 880-μm emission in IIZw40

Abstract

The central star-forming region in a blue compact dwarf galaxy, II Zw 40, was observed in the 340-GHz (880-) band at ∼5arcsec (250pc) resolution with the Submillimetre Array (SMA). A source associated with the central star-forming complex was detected with a flux of 13.6 ± 2.0mJy. The structure is more extended than the beam in the east-west direction. The SMA 880- flux is analysed by using theoretical models of radio spectral energy distribution along with centimetre interferometric measurements in the literature. We find that (i) the SMA 880- flux is dominated (∼75 per cent) by free-free emission from the central compact star-forming region and (ii) the contribution from dust emission to the SMA 880- flux is at most 4 ± 2.5mJy. We also utilize our models to derive the radio-far-infrared (FIR) relation of the II Zw 40 centre, suggesting that free-free absorption at low frequencies (several GHz; several cm) and the spatial extent of dust affect the radio-FIR relation. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.