{
  "id": "2008.01890",
  "version": "v1",
  "published": "2020-08-05T00:36:40.000Z",
  "updated": "2020-08-05T00:36:40.000Z",
  "title": "Merger rate density of Population III binary black holes below, above, and in the pair-instability mass gap",
  "authors": [
    "Ataru Tanikawa",
    "Hajime Susa",
    "Takashi Yoshida",
    "Alessandro A. Trani",
    "Tomoya Kinugawa"
  ],
  "comment": "37 pages, 33 figures, submitted to AAS journals",
  "categories": [
    "astro-ph.HE",
    "astro-ph.SR"
  ],
  "abstract": "We present the merger rate density of Population (Pop.) III binary black holes (BHs) by means of a widely-used binary population synthesis code {\\tt BSE} with extensions to very massive and extreme metal-poor stars. We consider not only low-mass BHs (lBHs: $5-50M_\\odot$) but also high-mass BHs (hBHs: $130-200M_\\odot$), where lBHs and hBHs are below and above the pair-instability mass gap ($50-130 M_\\odot$), respectively. Pop.~III BH-BHs can be categorized into three subpopulations: BH-BHs without hBHs (hBH0s: $m_{\\rm tot} \\lesssim 100M_\\odot$), with one hBH (hBH1s: $m_{\\rm tot} \\sim 140-260M_\\odot$), and with two hBHs (hBH2s: $m_{\\rm tot} \\sim 270-400M_\\odot$), where $m_{\\rm tot}$ is the total mass of a BH-BH. Their merger rate densities at the current universe are $\\sim 0.1$ yr$^{-1}$ Gpc$^{-3}$ for hBH0s, and $\\sim 0.01$ yr$^{-1}$ Gpc$^{-3}$ for the sum of hBH1s and hBH2s, using pessimistic Pop.~III star formation model. These rates are modestly insensitive to initial conditions and single star models. The hBH1 and hBH2 mergers can dominate BH-BHs with hBHs discovered in near future. They have low effective spins $\\lesssim 0.2$ in the current universe. The number ratio of the hBH2s to the hBH1s is high, $\\gtrsim 0.1$. We also find BHs in the mass gap (up to $\\sim 85 M_\\odot$) merge. These merger rates can be reduced to nearly zero if Pop.~III binaries are always wide ($\\gtrsim 100R_\\odot$), and if Pop.~III stars always enter into chemically homogeneous evolution. The presence of close Pop.~III binaries ($\\sim 10R_\\odot$) are crucial for avoiding the worst scenario.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-08-05T00:36:40.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "merger rate density",
      "binary black holes",
      "pair-instability mass gap",
      "binary population synthesis code"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 37,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}