Sign up to save your podcasts
Or
Share Compact jets dominate the continuum emission in low-luminosity active galactic nuclei
Share to email
Share to Facebook
Share to X
Share to email
Share to Facebook
Share to X
Or
Compact jets dominate the continuum emission in low-luminosity active galactic nuclei
Compact jets dominate the continuum emission in low-luminosity active galactic nuclei by J. A. Fernández-Ontiveros et al. on Monday 21 November
The disappearance of the accretion disc in low-luminosity active galactic
nuclei (LLAGN) leaves behind a faint optical nuclear continuum whose nature has
been largely debated, mainly due to serious observational limitations in the IR
to UV range. We combine multi-wavelength sub-arcsecond resolution observations
-- able to isolate the genuine nuclear continuum -- with nebular lines in the
mid-IR, to indirectly probe the shape of the extreme UV continuum. We found
that 8 of the nearest prototype LLAGN are compatible with pure compact jet
emission (self-absorbed synchrotron plus the associated self-Compton component)
over more than ten orders of magnitude in frequency. When compared with typical
radio galaxies, the LLAGN continua show two peculiarities: $i)$ a very steep
spectral slope in the IR-to-optical/UV range ($-3.7 < \alpha_0 < -1.3$; $F_\nu
\propto \nu^{\alpha_0}$); and $ii)$ a very high turnover frequency ($0.2-30\,
\rm{THz}$; $1.3\,\rm{mm}-10\,\rm{\mu m}$). These attributes can be explained if
the synchrotron continuum is mainly dominated by thermalised particles at the
jet base or corona with considerably high temperatures, whereas only a small
fraction of the energy ($\sim 20\%$) would be distributed along the high-energy
power-law tail of accelerated particles. On the other hand, the nebular gas
excitation in LLAGN is in agreement with photo-ionisation from inverse Compton
radiation ($\alpha_{\rm x} \sim -0.7$), which would dominate the nuclear
continuum shortwards of $\sim 3000$ \r{A}. Our results suggest that the LLAGN
continuum can be dominated at all wavelengths by undeveloped jets, powered by a
thermalised particle distribution, similar to the behaviour observed in compact
jets of quiescent black hole X-ray binaries. This has important implications in
the context of galaxy evolution, since LLAGN may represent a major but
underestimated source of kinetic feedback in galaxies.
arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.09828v1
View all episodes
By Corentin CadiouCompact jets dominate the continuum emission in low-luminosity active galactic nuclei by J. A. Fernández-Ontiveros et al. on Monday 21 November
The disappearance of the accretion disc in low-luminosity active galactic
nuclei (LLAGN) leaves behind a faint optical nuclear continuum whose nature has
been largely debated, mainly due to serious observational limitations in the IR
to UV range. We combine multi-wavelength sub-arcsecond resolution observations
-- able to isolate the genuine nuclear continuum -- with nebular lines in the
mid-IR, to indirectly probe the shape of the extreme UV continuum. We found
that 8 of the nearest prototype LLAGN are compatible with pure compact jet
emission (self-absorbed synchrotron plus the associated self-Compton component)
over more than ten orders of magnitude in frequency. When compared with typical
radio galaxies, the LLAGN continua show two peculiarities: $i)$ a very steep
spectral slope in the IR-to-optical/UV range ($-3.7 < \alpha_0 < -1.3$; $F_\nu
\propto \nu^{\alpha_0}$); and $ii)$ a very high turnover frequency ($0.2-30\,
\rm{THz}$; $1.3\,\rm{mm}-10\,\rm{\mu m}$). These attributes can be explained if
the synchrotron continuum is mainly dominated by thermalised particles at the
jet base or corona with considerably high temperatures, whereas only a small
fraction of the energy ($\sim 20\%$) would be distributed along the high-energy
power-law tail of accelerated particles. On the other hand, the nebular gas
excitation in LLAGN is in agreement with photo-ionisation from inverse Compton
radiation ($\alpha_{\rm x} \sim -0.7$), which would dominate the nuclear
continuum shortwards of $\sim 3000$ \r{A}. Our results suggest that the LLAGN
continuum can be dominated at all wavelengths by undeveloped jets, powered by a
thermalised particle distribution, similar to the behaviour observed in compact
jets of quiescent black hole X-ray binaries. This has important implications in
the context of galaxy evolution, since LLAGN may represent a major but
underestimated source of kinetic feedback in galaxies.
arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.09828v1