Journal Article

Gas and star formation in the Circinus galaxy

B.-Q. For, B. S. Koribalski and T. H. Jarrett

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 3, pages 1934-1950
Published in print September 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI:
Gas and star formation in the Circinus galaxy

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We present a detailed study of the Circinus galaxy, investigating its star formation, dust and gas properties, both in the inner and outer disc. To achieve this, we obtained high-resolution Spitzer mid-infrared images with the IRAC (3.6, 5.8, 4.5 and 8.0 μm) and MIPS (24 and 70 μm) instruments and sensitive H i data from the Australia Telescope Compact Array and the 64-m Parkes telescope. These were supplemented by CO maps from the Swedish-ESO Submillimetre Telescope. Because Circinus is hidden behind the Galactic plane, we demonstrate the careful removal of foreground stars as well as large- and small-scale Galactic emission from the Spitzer images. We derive a visual extinction of AV = 2.1 mag from the spectral energy distribution of the Circinus galaxy and total stellar and gas masses of 9.5 × 1010 and 9 × 109 M, respectively. Using various wavelength calibrations, we find obscured global star formation rates between 3 and 8 M yr−1. Star-forming regions in the inner spiral arms of Circinus, which are rich in H i, are beautifully unveiled in the Spitzer 8 μm image. The latter is dominated by polycyclic aromatic hydrocarbon (PAH) emission from heated interstellar dust. We find a good correlation between the 8 μm emission in the arms and regions of dense H i gas. The (PAH 8 μm)/24 μm surface brightness ratio shows significant variations across the disc of Circinus.

Keywords: galaxies: individual: Circinus; galaxies: spiral; galaxies: starburst; galaxies: star formation

Journal Article.  9483 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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