{
  "id": "2208.04970",
  "version": "v1",
  "published": "2022-08-09T18:00:23.000Z",
  "updated": "2022-08-09T18:00:23.000Z",
  "title": "Properties and Evolution of Dual and Offset AGN in the ASTRID Simulation at $z \\sim 2$",
  "authors": [
    "Nianyi Chen",
    "Tiziana Di Matteo",
    "Yueying Ni",
    "Michael Tremmel",
    "Colin DeGraf",
    "Yue Shen",
    "A. Miguel Holgado",
    "Simeon Bird",
    "Rupert Croft",
    "Yu Feng"
  ],
  "comment": "17 Pages, 18 Figures; comments welcome!",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We examine the dual (both BHs active) and offset (one BH active) AGN population (comprising $\\sim$ 2000 pairs at $0.5\\,\\text{kpc}\\lesssim\\Delta r<30\\,\\text{kpc}$) at $z=2\\sim3$ in the ASTRID simulation covering (360 cMpc)${^3}$. The dual (offset) AGN make up $3.0(2.2)\\%$ of all AGN at $z=2$. The dual fraction is roughly constant while the offset fraction increases by a factor of ten from $z=4\\sim2$. Compared with the full AGN population, duals are characterized by a low $M_\\text{BH}/M_*$ ratio, a high specific star-formation rate (sSFR) of $\\sim 1\\,\\text{Gyr}^{-1}$, and a high Eddington ratio ($\\sim 0.05$, double that of single AGN). The dual AGN are formed in major galaxy mergers (typically involving $M_\\text{halo}<10^{13}\\,M_\\odot$), with BHs that have similar masses. At small separations (when their host galaxies are in the late phase of the merger) duals become $2\\sim8$ times brighter (albeit more obscured) than at larger separations. $80\\%$ of these bright, close duals merge in the simulation within $\\sim500\\,\\text{Myrs}$. Notably, the initially less-massive BH in duals frequently becomes the brighter AGN during the galaxy merger. In offset AGN, the active BH is typically $\\gtrsim 10$ 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 center of massive halos ($ M_\\text{ halo}\\sim 10^{13-14}\\,M_\\odot$). 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 $\\Delta r\\sim5\\,\\text{kpc}$ for a few hundred Myrs.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-08-09T18:00:23.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "offset agn",
      "astrid simulation",
      "properties",
      "high specific star-formation rate",
      "full agn population"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}