INTEGRAL finds giant radio galaxies with multiple activity phases
Giant radio galaxies are able to launch jets of plasma that can reach
extensions up to a megaparsec. Thanks to their record size, these
plasmoids can exit the host galaxy, and break out into the intergalactic
medium. Only a small fraction of radio galaxies (6%) can reach such
extreme sizes, making them rare objects. The mechanism that activates
these spectacular cosmic spurts is not completely clear yet. The extreme
conditions produced by the strong magnetic field, formed by matter
spiralling into the supermassive black hole lurking at the center of
these galaxies, are thought to be the origin of the necessary electric
potential resulting in the acceleration of particles at a velocity
comparable to the speed of light.
During its long ongoing mission, INTEGRAL has scanned (and is still
scanning) the sky with the IBIS imager, and pin-pointed thousands of
high-energy cosmic sources emitting in the hard X-ray band. The galaxies
found among INTEGRAL sources have been cross-matched with catalogues
available from radio telescopes (at the opposite end of the
electro-magnetic spectrum!) to detect and locate radio galaxies with
giant-sized jets. Data from the new-generation radio survey LoTSS (LOFAR
Two-metre Sky Survey) have been used to study with unprecedented detail
the morphology produced by these jets along millions of years, unveiling
hints of multiple activity phases stratified along time. In some cases,
images suggest that the jets even changed their direction, leading to
X-shaped structures. Finally, a comparison of these hard X-ray selected
giant radio galaxies with the radio-selected ones from the LoTSS survey
suggests that, on average, they can reach larger sizes. An investigation
of the possible selection biases, through the study of a control sample
of giant radio galaxies, is ongoing.
The unique synergy between INTEGRAL and the new generation radio
telescopes will allow us to reveal more of these objects, and finally
study their life-cycle and the conditions necessary to trigger these
spectacular sky phenomena.
Caption:
Radio galaxy J0318+684: overlay of the radio emissions detected by LOFAR
at 144 MHz (in red) on the optical image from DSS2. The scale is reported
on the lower-left corner.
