Bibcode
Fernández-Ontiveros, J. A.; López-Gonzaga, N.; Prieto, M. A.; Acosta-Pulido, J. A.; Lopez-Rodriguez, E.; Asmus, D.; Tristram, K. R. W.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 4, p.5377-5393
Advertised on:
6
2019
Citations
16
Refereed citations
15
Description
The feeble radiative efficiency characteristic of Low-Luminosity Active
Galactic Nuclei (LLAGNs) is ascribed to a sub-Eddington accretion rate,
typically at log (Lbol/Ledd) ≲ -3. At the
finest angular resolutions that are attainable nowadays using
mid-infrared (mid-IR) interferometry, the prototypical LLAGN in NGC 1052
remains unresolved down to < 5 {mas} (0.5 {pc}). This is in line with
non-thermal emission from a compact jet, a scenario further supported by
a number of evidences: the broken power-law shape of the continuum
distribution in the radio-to-UV range; the {˜ } 4{{ per cent}}
degree of polarization measured in the nuclear mid-IR continuum,
together with the mild optical extinction (A_V ˜ 1 {mag}); and the
`harder when brighter' behaviour of the X-ray spectrum, indicative of
self-Compton synchrotron radiation. A remarkable feature is the
steepness of the IR-to-UV core continuum, characterized by a power-law
index of ˜2.6, as compared to the canonical value of 0.7.
Alternatively, to explain the interferometric data by thermal emission
would require an exceptionally compact dust distribution when compared
to those observed in nearby AGN, with A_V ≳ 2.8 {mag} to account
for the IR polarization. This is in contrast with several observational
evidences against a high extinction along the line of sight, including
the detection of the nucleus in the UV range and the well-defined shape
of the power-law continuum. The case of NGC 1052 shows that compact jets
can dominate the nuclear emission in LLAGN across the whole
electromagnetic spectrum, a scenario that might be common among this
class of active nuclei.
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