The extended X-ray emission around HDF 130 at z = 1.99: An inverse Compton ghost of a giant radio source in the Chandra Deep Field-North

Abstract

One of the six extended X-ray sources found in the Chandra Deep Field-North is centred on Hubble Deep Field (HDF) 130, which has recently been shown to be a massive galaxy at z=1.99 with a compact radio nucleus. The X-ray source has a roughly double-lobed structure with each lobe about 41-arcsec long, or 345 kpc at the redshift of HDF 130. We have analysed the 2 Ms X-ray image and spectrum of the source and find that it is well fit by a power-law continuum of photon index 2.65 and has a 2-10 keV luminosity of 5.4 × 1043 erg s-1 (if at z = 1.99). Any further extended emission within a radius of 60 arcsec has a luminosity less than half this value, which is contrary to what is expected from a cluster of galaxies. The source is best explained as an inverse Compton ghost of a giant radio source, which is no longer being powered, and for which Compton losses have downgraded the energetic electrons, γ > 104, required for high-frequency radio emission. The lower energy electrons, γ ~ 1000, produce X-rays by inverse Compton scattering on the cosmic microwave background. Depending on the magnetic field strength, some low-frequency radio emission may remain. Further inverse Compton ghosts may exist in the Chandra Deep Fields and beyond. © 2009 The Authors. Journal compilation © 2009 RAS.