What do Active Galactic Nuclei (AGN) observed by INTEGRAL look like
in the radio band? With the aim of answering this question, radio data
from the NRAO VLA Sky Survey survey (NVSS) and the Sydney University
Molonglo Sky Survey (SUMSS) of a complete sample of INTEGRAL AGN have
been analysed. The INTEGRAL sample is characterized both by radio-quiet
and radio-loud AGN, with a prevalence of radio-quiet objects. Most
AGN (89%) have a radio counterpart displaying a wide range of morphologies,
showing an unresolved or slightly resolved core in some cases, and
evident extended emission in others. The linear sizes of the extended
emission in the latter ranges from kpc to hundreds of kpc's (the images
of the four typical morphological types are shown in the figure, lower
left panel). In particular, some sources show the triple or double emitting
structures typically found in powerful radio galaxies (see the multi-frequency
image of the galaxy Centaurus A belonging to the INTEGRAL sample in the
figure, upper left).
Accelerated particles in jets may constitute one of the possible sources
of AGN feedback into the interstellar matter of the host galaxy. Indeed,
how the jet emission (in the radio) is connected with the accretion
emission (in X-rays and hard X-rays) is one of the key ingredients in
the AGN-galaxy evolutionary models. The existence of a correlation
between the radio and the X-ray luminosity has been largely observed in
accreting systems and different correlation slopes can be interpreted in
the framework of a radiatively efficient or inefficient accretion.
Panessa et al. (2014) find the existence of a significant correlation
between the X-ray (2-10 keV) and hard X-ray (20-100 keV) luminosities and
the 1.4 GHz radio luminosities in the INTEGRAL sample (in the upper right
panel of figure, the 1.4 GHz peak luminosity correlates with the 20-100 keV
luminosity, with different symbols corresponding to different radio
morphologies). The correlation slopes are found to be clearly steeper than
the classical value of 0.6 found for radiatively inefficient accreting
systems but consistent with the value of 1.4 expected for sources belonging
to the efficient accretion branch. This suggests that the INTEGRAL AGN are
accretion dominated sources, i.e. objects which are accreting at high
Eddington rates and where the high energy emission from the central engine
is related to the radio emission averaged over kpc scales.
Reference:
"The 1.4 GHz radio properties of hard X-ray selected AGN"
Panessa, F.; Tarchi, A.; Castangia, P.; Maiorano, E.; Bassani, L.;
Bicknell, G.; Bazzano, A.; Bird, A. J.; Malizia, A.; Ubertini, P. http://xxx.lanl.gov/abs/1411.7829
2014, accepted for publication in MNRAS (eprint arXiv:1411.7829)
Credits multi-frequency image of the galaxy Centaurus A:
