Near-infrared line and radio continuum imaging of the Circinus galaxy

Abstract

We have imaged the Circinus galaxy in the near-infrared [Fe ii] 1.64-μm and H2 2.12-μm lines, and derived velocity maps for the emission. The morphologies are strikingly different, but the velocity maps are very similar and consistent with simple rotation. We also present new radio continuum maps at 3 and 6 cm, which show a partially resolved nucleus with a flat spectral index. This suggests free–free absorption rather than self-absorption in a compact source. There is some evidence of radio jets close to the nucleus. The H2 emission, rather than the [Fe ii] as in NGC 1068, is extended along the jet axis and may be excited by jet-induced shocks either in a low-density medium or with rather slow shock speeds (v≲50 km s−1). We find that the star formation in the ring 10 arcsec from the nucleus began less than a few ×107 yr ago. Nearer the AGN, perhaps in and around the inferred torus, we detect extended [Fe ii] emission (including one prominent peak about 2 arcsec north of the AGN which could be due to a single young remnant), from which we derive a modest star formation rate of <1 M⊙ yr−1.