The nature of the IR emission in LLAGN at parsec scales
Does the jet dominate at low-luminosities?
1 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, Bonn, D–53121, Germany
2 Instituto de Astrofísica de Canarias (IAC), Vía Láctea s/n, La Laguna, E–38200, Spain
3 Departamento de Astrofísica, Facultad de Física, Universidad de La Laguna, Astrofísico Fco. Sánchez s/n, La Laguna, E–38207, Spain
4 Astronomical Institute “Anton Pannekoek”, 1098 XH Amsterdam, Netherlands
a e-mail: email@example.com
Published online: 9 December 2013
The vast majority of AGN belong to the low-luminosity class (LLAGN): they exhibit a low radiation effciency (L ≲ 1042 erg s−1; L/Ledd ≲ 10−3) and the absence of the big blue bump in their spectrum, a signature of the accretion disk. The study of LLAGN is a complex task due to the contribution of the host galaxy, whose light outshines these faint nuclei. As a consequence, numerical models are usually compared with relatively poorly defined spectral energy distributions (SEDs). For a sample of six prototype nearby LLAGN, a multiwavelength dataset including radio, IR, optical/UV and X-ray measurements with a few tenths of arcsec resolution has been collected. These high-spatial resolution SEDs reveal that: i) the mid-IR bump, indicative of thermal emission from the torus, is missing in LLAGN; ii) the continuum emission of these nuclei is largely described by a self-absorbed synchrotron spectrum, suggesting that jet emission dominates the overall energy output in these objects. The optically thin radiation in the IR-to-UV range is produced in the jet launching region, very close to the central black hole. The very steep slope found in this component –with a spectral index in the 1-3 range– suggests that a large number of LLAGN are powered by young and compact jets with very high radiative losses.
© Owned by the authors, published by EDP Sciences, 2013
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