The Centimeter to Submillimeter Broad Band Radio Spectrum of the Central Compact Component in A Nearby Type-II Seyfert Galaxy NGC 1068

TL;DR

This study analyzes the broadband radio spectrum of NGC 1068's central region using ALMA and VLA data, suggesting emission from jet base, dusty torus, and corona, and highlights the need for future high-resolution observations.

Contribution

It updates previous models of NGC 1068's radio spectrum by incorporating new 100 GHz data and proposes a combined emission model involving jet, torus, and corona components.

Findings

Flux density between 10-20 mJy at 5-700 GHz

Model adjustments needed to fit new data point

Magnetic field strength estimated at 20 G

Abstract

We analyze all the available Atacama Large Millimeter / submillimeter Array archival data of the nearby Type-II Seyfert galaxy NGC 1068, including new 100 GHz data with the angular resolution of 0\farcs05, which was not included in previous continuum spectral analysis. By combining with the literature data based on the Very Large Array, we investigate the broadband radio continuum spectrum of the central $\lesssim7$ pc region of NGC 1068. We found that the flux density is between $\approx$10-20 mJy at 5-700 GHz. Due to the inability of the model in previous studies to account for the newly added 100 GHz data point, we proceeded to update the models and make the necessary adjustments to the parameters. One possible interpretation of this broadband radio spectrum is a combination of emission from the jet base, the dusty torus, and the compact X-raying corona with the magnetic field strength of $\approx20$ G on scales of $\approx30$ Schwarzschild radii from the central black hole. In order to firmly identify the compact corona by omitting any other possible extended components (e.g., free-free emission from ionized gas around), high-resolution/sensitivity observations achieved by next-generation interferometers will be necessary.