Searching for nucleus obscuration in the infrared spectra of nearby FR-I radio galaxies
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Why are there so many types of active galactic nuclei (AGN)? Astronomers have proposed numerous AGN unification models to explain the vast array of different AGN types with a single type of object. The most prominent of these features a supermassive black hole’s accretion disk obscured by a torus of discrete dusty clouds. The applicability of this model to low-luminosity AGN such as Fanaroff & Riley class I (FR-I) radio galaxies is controversial. We present a wide-band infrared spectroscopic analysis of ten nearby FR-I radio galaxies. We used Markov-chain Monte Carlo algorithms to fit a set of models to Spitzer /IRS spectra with wide-band behaviour constrained by photometry from 2MASS, Spitzer /IRAC, Spitzer /MIPS, and Herschel /SPIRE. We find one galaxy is best fit by a torus and three others show some thermal mid-infrared component. We conclude that 40% of our FR-I radio galaxies show evidence of obscuring dusty material.