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