A cosmic dance at z~3: Detecting the host galaxies of the dual AGN system LBQS0302-0019 and Jil with HAWK-I+GRAAL

Abstract

We recently discovered that the luminous radio-quiet QSO LBQS0302-0019 at z=3.286 is likely accompanied by an obscured AGN at 20kpc projected distance, which we dubbed Jil. It represents the tightest candidate obscured/unobscured dual AGN system at z>3. To verify the dual AGN scenario we obtained deep \(K_s\) band (rest-frame \(V\) band) imaging with the VLT/HAWK-I+GRAAL instrument at 0.4" resolution during science verification in January 2018. Indeed, we detect the individual host galaxies of the QSO and Jil with estimated stellar masses of \(\log(M_\star/M_{\odot})=11.4\pm0.5\) and \(\log(M_\star/M_{\odot})=10.9\pm0.5\), respectively. Near-IR spectra obtained with VLT-KMOS reveal a clear [OIII] \(\lambda\)5007 line detection at the location of Jil which does not contribute significantly to the \(K_s\) band flux. Both observations therefore corroborate the dual AGN scenario. A comparison to Illustris cosmological simulations suggests a parent halo mass of \(\log(M_\mathrm{halo}/M_{\odot})=13.2\pm0.5\) for this interacting galaxy system, corresponding to a very massive dark matter halo at that epoch.