RT info:eu-repo/semantics/masterThesis
T1 Unveiling the Ionisation Continuum in Low-Luminosity AGN
A1 López López, Xavier
A2 Máster Universitario en Astrofísica
AB The accretion disc of low-luminosity active galactic nuclei (LLAGN) is predicted to disappear atlow Eddington ratios (Lbol/Ledd < −3), while high-angular resolution observations of these nuclei haverevealed a steep power law optical/UV continuum with α ∼ 2 (Fν ∼ ν−α), characteristic of synchrotronemission. However, hydrogen absorption makes it impossible to probe this continuum shortwards of∼ 1000 Å, and thus the possible contribution of an accretion disc cannot be fully discarded. Still, thisinformation is encoded in the fine structure lines produced by the AGN ionised gas, whose relativeintensities are sensitive to the shape of the ionising continuum and therefore can be used to probe thepresence of the accretion disc. In this work we have combined diffraction-limited high-angular resolutionobservations from the Hubble Space Telescope in the optical/UV range and the Very Large Telescopein the near- to mid-infrared (IR) range for a sample of 10 LLAGN. These direct measurements of theaccessible part of the LLAGN continuum have been combined with photo-ionisation simulations usingCloudy and mid-IR fine-structure lines observed by Spitzer, to infer the shape of the missing continuumbelow ∼ 1000 Å. This approach allowed us to reconstruct the primary ionising spectra and the disccontribution in prototypical LLAGN nuclei such as M87, NGC 1052, or the Sombrero galaxy. The IRemission line properties of the LLAGN in our sample can be reproduced by a power law continuumextending from the UV to the X-ray range, with a typical index of 0.35 . α . 0.55, with a negligible orno contribution at all from the accretion disc to the ionisation. These accretion discs must be truncatedor in a cool state in order to explain the lack of ionising photons. The power law component dominatingthe extreme UV continuum in LLAGN is associated with inverse Compton emission from reprocessedsynchrotron jet emission by the black hole corona. This is supported by photo-ionisation predictions forjet models applied to three of the LLAGN in our sample.
YR 2021
FD 2021
LK http://riull.ull.es/xmlui/handle/915/23099
UL http://riull.ull.es/xmlui/handle/915/23099
LA es
DS Repositorio institucional de la Universidad de La Laguna
RD 13-may-2024