{
  "id": "2306.04041",
  "version": "v1",
  "published": "2023-06-06T22:13:55.000Z",
  "updated": "2023-06-06T22:13:55.000Z",
  "title": "Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Investigating the Nature of J0823+2418 at $z=1.81$: a Likely Lensed Quasar",
  "authors": [
    "Arran C. Gross",
    "Yu-Ching Chen",
    "Adi Foord",
    "Xin Liu",
    "Yue Shen",
    "Masamune Oguri",
    "Andy Goulding",
    "Hsiang-Chih Hwang",
    "Nadia Zakamska",
    "Yilun Ma",
    "Liam Nolan"
  ],
  "comment": "25 pages, 14 figures, submitted to ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Dual quasars at small physical separations are an important precursor phase of galaxy mergers, ultimately leading to the coalescence of the two supermassive black holes. Starting from a sample of dual/lensed quasar candidates discovered using astrometric jitter in Gaia data, we present a pilot case study of one of the most promising yet puzzling candidate dual quasars at cosmic noon (z$\\sim$1.8). Using multi-wavelength imaging and spectroscopy from X-ray to radio, we test whether the J0823+2418 system is two individual quasars in a bound pair at separation$\\sim$0.64'', or instead a single quasar being gravitationally lensed by a foreground galaxy. We find consistent flux ratios ($\\sim$1.25-1.45) between the two sources in optical, NIR, UV, and radio, and thus similar spectral energy distributions, suggesting a strong lensing scenario. However, differences in the radio spectral index, as well as changing X-ray fluxes, hint at either a dual quasar with otherwise nearly identical properties, or perhaps lensing-based time lag of $\\sim$3 days paired with intrinsic variability. We find with lens mass modeling that the relative NIR positions and magnitudes of the two quasars and a marginally detected central galaxy are consistent with strong lensing. Archival SDSS spectra likewise suggest a foreground absorber via Mg II absorption lines. We conclude that J0823+2418 is likely a lensed quasar, and therefore that the VODKA sample contains a population of these lensed systems (perhaps as high as 50%) as well as dual quasars.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-06-06T22:13:55.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "dual sub-kpc agn",
      "lensed quasar",
      "off-nucleus",
      "similar spectral energy distributions",
      "varstrometry"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 25,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}