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 $\log (M_{\star }/M_{\odot })=11.4\pm 0.5$ and $\log (M_{\star }/M_{\odot })=10.9\pm 0.5$, respectively. Near-IR spectra obtained with VLT-KMOS reveal a clear [OIII] $\hat{I}»$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 $\log (M_{\mathrm{halo}}/M_{\odot })=13.2\pm 0.5$ for this interacting galaxy system, corresponding to a very massive dark matter halo at that epoch.

4 pages, 4 figures, accepted for publication in A&A letters