2021MNRAS.505.1543H -
Mon. Not. R. Astron. Soc., 505, 1543-1556 (2021/July-3)
Proof of CMB-driven X-ray brightening of high-z radio galaxies.
HODGES-KLUCK E., GALLO E., GHISELLINI G., HAARDT F., WU J. and CIARDI B.
Abstract (from CDS):
We present a definitive assessment of the role of inverse Compton scattering of cosmic microwave background photons (IC/CMB) in the context of radio galaxies. Owing to the steep increase of the CMB radiation energy density, IC/CMB is supposed to become progressively more important with respect to radio synchrotron cooling as the redshift increases. For typical energies at play, this process will up-scatter the CMB photons into the X-ray band, and is thus expected to yield a redshift-dependent, concurrent X-ray brightening and radio dimming of the jet-powered structures. Here, we show how a conclusive proof of this effect hinges on high-resolution imaging data in which the extended lobes can be distinguished from the compact hotspots where synchrotron self-Compton dominates the X-ray emission regardless of redshift. We analyse Chandra and Very Large Array data of 11 radio galaxies between 1.3 ≲z ≲4.3, and demonstrate that the emission from their lobes is fully consistent with the expectations from IC/CMB in equipartition. Once the dependence on size and radio luminosity are properly accounted for, the measured lobe X-ray luminosities bear the characteristic ∝(1 + z)4 proportionality expected of a CMB seed radiation field. Whereas this effect can effectively quench the (rest-frame) GHz radio emission from z ≳3 radio galaxies below ≲1 mJy, IC/CMB alone cannot be responsible for a deficit in high-z, radio-loud active galactic nuclei (AGNs) if - as we argue - such AGNs typically have bright, compact hotspots.
Abstract Copyright:
© Published by Oxford University Press on behalf of The Royal Astronomical Society 2021.
Journal keyword(s):
radiation mechanisms: non-thermal - galaxies: active - galaxies: high-redshift - galaxies: jets - X-rays: galaxies
Simbad objects:
15
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2021MNRAS.505.1543H and select 'bookmark this link' or equivalent in the popup menu