{
  "id": "2301.07360",
  "version": "v1",
  "published": "2023-01-18T08:08:33.000Z",
  "updated": "2023-01-18T08:08:33.000Z",
  "title": "MAMMOTH-Subaru V. Effects of Cosmic Variance on Ly$α$ Luminosity Functions at $z=2.2-2.3$",
  "authors": [
    "Ke Ma",
    "Haibin Zhang",
    "Zheng Cai",
    "Yongming Liang",
    "Nobunari Kashikawa",
    "Mingyu Li",
    "Yunjing Wu",
    "Qiong Li",
    "Xiaohui Fan",
    "Sean D. Johnson",
    "Masami Ouchi"
  ],
  "comment": "14 pages, 7 figures",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-z Universe with a small volume, such uncertainties produce the field-to-field variance of galaxy number $\\sigma_{g}$ in observational astronomy. This uncertainty significantly affects the Luminosity Functions (LF) measurement of Lya Emitters (LAEs). For most previous Lya LF studies, $\\sigma_{g}$ is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for $z\\approx2.2$ Lya LFs. The LAE candidates are observed using narrowband and broadband of the Subaru/Hyper Suprime-Cam (HSC), with 8 independent fields, making the total survey area $\\simeq11.62$deg$^2$ and a comoving volume of $\\simeq8.71\\times10^6$Mpc$^3$. These eight fields are selected using the project of MAMMOTH. We report a best-fit Schechter function with parameters $\\alpha=-1.75$ (fixed), $L_{Ly\\alpha}^{*}=5.18_{-0.40}^{+0.43} \\times 10^{42}$erg s$^{-1}$ and $\\phi_{Lya}^{*}=4.87_{-0.55}^{+0.54}\\times10^{-4}$Mpc$^{-3}$ for the overall Lya LFs. After clipping out the regions that can bias the cosmic variance measurements, we calculate $\\sigma_{g}$, by sampling LAEs within multiple pointings assigned on the field image. We investigate the relation between $\\sigma_{g}$ and survey volume $V$, and fit a simple power law: $\\sigma_g=k\\times(\\frac{V_{\\rm eff}}{10^5 {\\rm Mpc}^3})^{\\beta}$. We find best-fit values of $-1.209_{-0.106}^{+0.106}$ for $\\beta$ and $0.986_{-0.100}^{+0.108}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs might be larger than that of general star-forming galaxies.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-01-18T08:08:33.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "luminosity functions",
      "galaxy number density properties",
      "mammoth-subaru",
      "best-fit schechter function",
      "total survey area"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}