Properties and evolution of dual and offset AGN in the ASTRID simulation at z 2

We examine the dual [both black hole (BH) active] and offset (one BH active and in distinct galaxies) active galactic nucleus (AGN) population (comprising similar to 2000 pairs at 0.5 kpc less than or similar to Delta r < 30 kpc) at z = 2 similar to 3 in the ASTRID simulation covering (360 cMpc)(3). The dual (offset) AGN make up 3.0(0.5) per cent of all AGN at z = 2. The dual fraction is roughly constant while the offset fraction increases by a factor of 10 from z = 4 similar to 2. Compared with the full AGN population, duals are characterized by low M-BH/M-* ratios, high specific star formation rates (sSFR) of similar to 1 Gyr(-1), and high Eddington ratios (similar to 0.05, double that of single AGN). Dual AGNs are formed in major galaxy mergers (typically involving M-halo < 10(13) M-circle dot), with simular-mass BHs. At small separations (when host galaxies are in the late phase of the merger), duals become 2 similar to 8 times brighter (albeit more obscured) than at larger separations. 80 per cent of the bright, close duals would merge within similar to 500 Myr. Notably, the initially less-massive BHs in duals frequently become the brighter AGN during galaxy mergers. In offset AGN, the active BH is typically greater than or similar to 10 times more massive than its non-active counterpart and than most BHs in duals. Offsets are predominantly formed in minor galaxy mergers with the active BH residing in the centre of massive haloes (M-halo similar to 10(13-14) M-circle dot). In these deep potentials, gas stripping is common and the secondary quickly deactivates. The stripping also leads to inefficient orbital decay amongst offsets, which stall at Delta r similar to 5 kpc for a few hundred Myrs.