Journal Article

Central free–free dominated 880-μm emission in II Zw 40

Hiroyuki Hirashita

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 418, issue 2, pages 828-837
Published in print December 2011 | ISSN: 0035-8711
Published online November 2011 | e-ISSN: 1365-2966 | DOI:
Central free–free dominated 880-μm emission in II Zw 40

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The central star-forming region in a blue compact dwarf galaxy, II Zw 40, was observed in the 340-GHz (880-) band at ∼5 arcsec (250 pc) resolution with the Submillimetre Array (SMA). A source associated with the central star-forming complex was detected with a flux of 13.6 ± 2.0 mJy. 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 ± 2.5 mJy. 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.

Keywords: dust, extinction; H ii regions; galaxies: dwarf; galaxies: evolution; galaxies: individual: II Zw 40; submillimetre: galaxies

Journal Article.  8035 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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