No AGN evidence in NGC 1614 from deep radio VLBI observations

Abstract

We present deep dual-band 5.0 and 8.4 GHz European VLBI Network (EVN) observations of NGC 1614, a local luminous infrared galaxy with a powerful circumnuclear starburst ring, and whose nuclear engine origin is still controversial. We aim at detecting and characterizing compact radio structures both in the nuclear region and in the circumnuclear ring. We do not find any compact source in the central 200 pc region, setting a very tight 5σ upper limit of 3.7 × 10 36 erg s −1 and 5.8 × 10 36 erg s −1 , at 5.0 and 8.4 GHz, respectively. However, we report a clear detection at both frequencies of a compact structure in the circumnuclear ring, 190 pc to the north of the nucleus, whose luminosity and spectral index are compatible with a core-collapse supernova, giving support to the high star formation rate in the ring. Our result favors the pure starburst scenario, even for the nucleus of NGC 1614, and shows the importance of radio VLBI observations when dealing with the obscured environments of dusty galaxies.

Infrared Colours and Spectral Energy Distributions of Hard X-ray Selected Obscured and Compton-thick AGN

“…Its earlier X-ray observations with ASCA suggest the presence of an AGN based on the well fitted power-law in the 2-10 keV band (Risaliti et al 2000). Although the weak hard Xray emission indicates a Compton-thick AGN at the first place, the multi-wavelength observations in sub-millimetre (Xu et al 2015), radio (Herrero-Illana et al 2017) and X-rays (Pereira-Santaella et al 2011;Herrero-Illana et al 2014) do not support this. Xu et al (2015) found that the amount of nuclear molecular gas and dust is much lower than that predicted for CT AGNs.…”