A 100-kpc inverse Compton X-ray halo around 4C60.07 at z=3.79

TL;DR

This study reports the discovery of a large inverse Compton X-ray halo around a high-redshift radio galaxy, revealing insights into galaxy formation and the role of energetic processes at early cosmic times.

Contribution

It presents the first detailed analysis of a 100-kpc inverse Compton X-ray halo at z>3, linking it to galaxy formation and merger activity.

Findings

Extended X-ray emission with Lx~10^45 erg/s detected

X-ray halo morphology similar to radio and Ly-alpha emission

Presence of two nearby active galactic nuclei indicating mergers

Abstract

We analyse a 100-ks Chandra observation of the powerful radio galaxy, 4C60.07 at z=3.79. We identify extended X-ray emission with Lx~10^45 erg/s across a ~90-kpc region around the radio galaxy. The energetics of this X-ray halo and its morphological similarity to the radio emission from the galaxy suggest that it arises from inverse Compton (IC) scattering, by relativistic electrons in the radio jets, of Cosmic Microwave Background photons and potentially far-infrared photons from the dusty starbursts around this galaxy. The X-ray emission has a similar extent and morphology to the Ly-alpha halo around the galaxy, suggesting that it may be ionising this halo. Indeed we find that the GHz-radio and X-ray and Ly-alpha luminosities of the halo around 4C60.07 are identical to those of 4C41.17 (also at z=3.8) implying that these three components are linked by a single physical process. This is only the second example of highly-extended IC emission known at z>3, but it underlines the potential importance of IC emission in the formation of the most massive galaxies at high redshifts. In addition, we detect two X-ray luminous active galactic nuclei (AGN) within ~30kpc of the radio galaxy. These two companion AGN imply that the radio and starburst activity in the radio galaxy is triggered through multiple mergers of massive progenitors on a short timescale, ~100Myrs. These discoveries demonstrate the wealth of information which sensitive X-ray observations can yield into the formation of massive galaxies at high redshifts.