The circumnuclear environment of NGC 613: a nuclear starburst caught in the act?

We present near-infrared (H- and K-band) integral-field observations of the inner ~700 pc of the active spiral galaxy NGC 613, obtained with SINFONI on the Very Large Telescope. We use emission-line ratios to determine the dominant excitation mechanisms in different regions within our field of view, in particular, the active nucleus and the star-forming circumnuclear ring. Diagnostic diagrams involving [Fe II] and H₂ fluxes indicate that the gas is not only photoionized by the active galactic nucleus (AGN) in the nucleus of NGC 613, but also shock heated. On the other hand, the emission-line ratios measured in the 'hotspots' along the ring are fully consistent with them being young star-forming regions. We find no sign of radial gas transport from the ring into the core region dominated by the AGN. The ring morphology appears disturbed by a radial outflow of material from the AGN, which is confirmed by the existence of a weak jet in archival radio maps. However, this jet does not seem to have any significant effect on the morphology of the large (∼8 × 10⁷ M_⊙) reservoir of molecular gas that has accumulated inside the central ∼100 pc. Such a concentration of molecular gas around an AGN is unusual, and c. In this context, NGC 613 appears to be in final stages of the gas accumulation phase and is likely to undergo a nuclear starburst in the near future.