A Compact Jet at the Infrared Heart of the Prototypical Low-Luminosity AGN in NGC 1052. (arXiv:1903.05108v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_Ontiveros_J/0/1/0/all/0/1">J.A. Fernández-Ontiveros</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Gonzaga_N/0/1/0/all/0/1">N. López-Gonzaga</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prieto_M/0/1/0/all/0/1">M.A. Prieto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Acosta_Pulido_J/0/1/0/all/0/1">J.A. Acosta-Pulido</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Rodriguez_E/0/1/0/all/0/1">E. Lopez-Rodriguez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Asmus_D/0/1/0/all/0/1">D. Asmus</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tristram_K/0/1/0/all/0/1">K.R.W. Tristram</a>
The feeble radiative efficiency characteristic of Low-Luminosity Active
Galactic Nuclei (LLAGN) is ascribed to a sub-Eddington accretion rate,
typically at $log(L_{rm bol}/L_{rm edd}) lesssim -3$. 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
$< 5, rm{mas}$ ($0.5, rm{pc}$). 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 $sim 4%$ degree of polarisation measured in the nuclear mid-IR continuum,
together with the mild optical extinction ($A_V sim 1, rm{mag}$); 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, characterised by a power-law index of $sim 2.6$,
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 $A_V
gtrsim 2.8, rm{mag}$ to account for the IR polarisation. 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.
The feeble radiative efficiency characteristic of Low-Luminosity Active
Galactic Nuclei (LLAGN) is ascribed to a sub-Eddington accretion rate,
typically at $log(L_{rm bol}/L_{rm edd}) lesssim -3$. 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
$< 5, rm{mas}$ ($0.5, rm{pc}$). 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 $sim 4%$ degree of polarisation measured in the nuclear mid-IR continuum,
together with the mild optical extinction ($A_V sim 1, rm{mag}$); 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, characterised by a power-law index of $sim 2.6$,
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 $A_V
gtrsim 2.8, rm{mag}$ to account for the IR polarisation. 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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