2016MNRAS.457L.122H

We present high-resolution (0.3 arcsec) Atacama Large Millimeter Array (ALMA) 870 µm imaging of five z ≃ 1.5-4.5 X-ray detected AGN (with luminosities of L2-8keV > 10⁴² erg /s). These data provide a >=20 times improvement in spatial resolution over single-dish rest-frame far-infrared (FIR) measurements. The sub-millimetre emission is extended on scales of FWHM ≃ 0.2 arcsec-0.5 arcsec, corresponding to physical sizes of 1-3 kpc (median value of 1.8 kpc). These sizes are comparable to the majority of z=1-5 sub-millimetre galaxies (SMGs) with equivalent ALMA measurements. In combination with spectral energy distribution analyses, we attribute this rest-frame FIR emission to dust heated by star formation. The implied star-formation rate surface densities are ≃20-200 M☉ yr^–1 kpc^–2, which are consistent with SMGs of comparable FIR luminosities (i.e. LIR ≃ [1-5] x 10¹² L☉). Although limited by a small sample of AGN, which all have high-FIR luminosities, our study suggests that the kpc-scale spatial distribution and surface density of star formation in high-redshift star-forming galaxies is the same irrespective of the presence of X-ray detected AGN.