A meeting at <i>z</i> ∼ 3: Young massive galaxies and an AGN within 30 kpc of the luminous QSO LBQS 0302–0019

Context. Contrary to expectations from scenarios of black hole growth driven by galaxy interactions and mergers, dual active galactic nuclei (AGN) with kiloparsec separations are rarely observed very difficult identify, in particular at high redshifts (i.e. z &gt; 2). Aims. Focussing on the recently discovered AGN system LBQS 0302−0019 = 3.29, we seek identify further group members its environment understand their formation history through deep high-angular-resolution imaging. Methods. We present Hubble Space Telescope (HST) Wide-field Camera 3 near-infrared imaging 0302−0019. In combination ground-based VLT/HAWK-I imaging, infer accurate sizes, colours, ages, stellar masses companion galaxies. Results. clearly detect four objects close that also have faint signatures images. constrain light-weighted ages for two most prominent companions, Jil1 Jil2, t ⋆ 252 −109 +222 Myr log( M /[ ⊙ ]) 11.2 −0.1 +0.3 19 −14 +74 9.4 −0.4 +0.9 , respectively. The HST data show obscured AGN, previously identified strong nebular He II emission, is associated young massive Jil2. Because stars starburst cannot be solely responsible strengthen our initial conclusion Jil2 has been hosting an AGN. Conclusions. If had accompanied sustained growth, may contributed -ionising flux create large Ly α proximity zone around Hence, duration current luminous episode overestimated.