{
  "id": "2310.12205",
  "version": "v1",
  "published": "2023-10-18T18:00:02.000Z",
  "updated": "2023-10-18T18:00:02.000Z",
  "title": "Variations of Interstellar Gas-to-Dust Ratios at High Galactic Latitudes",
  "authors": [
    "J. Michael Shull",
    "Georgia V. Panopoulou"
  ],
  "comment": "37 pages, 7 tables, 8 figures, submitted to Astrophysical Journal",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "Interstellar dust at high Galactic latitudes can influence astronomical foreground subtraction, produce diffuse scattered light, and result in harder (de-reddened) ultraviolet spectra of quasars. In a sample of 94 quasars at high latitude and low extinction, we evaluate the interstellar \"gas-to-dust ratio\", $N_{\\rm H}/E(B-V)$, using hydrogen column densities (H I and H$_2$) and far-infrared estimates of dust reddening. In the Galactic plane, this ratio is $6.0\\pm0.2$ (in units of $10^{21}~{\\rm cm}^{-2}~{\\rm mag}^{-1}$). In a sub-sample of 51 quasars with measurements of both H I and H$_2$ and $0.01 \\leq E(B-V) \\lesssim 0.1$, we find mean ratios $10.3\\pm0.4$ (gas at all velocities) and $9.2\\pm0.3$ (low velocity only). Including H$_2$ increases $N_{\\rm H}$ by $\\sim10$%, even at high latitude. On average, recent Planck estimates of $E(B-V)$ in low reddening sight lines are 12% higher than those from Schlafly & Finkbeiner (2011), and $N_{\\rm HI}$ exhibits significant variations when measured at different radio telescopes. We also show that $E(B-V)$ is sensitive to far-infrared modeled dust temperature $T_d$ and emissivity index $\\beta$. Consequently, gas-to-dust ratios have large, asymmetric errors at low $E(B-V)$. The ratios are elevated in sight lines with high-velocity clouds, which contribute $N_{\\rm H}$ but little reddening. In Complex C, the ratio decreases by 40% when high velocity gas is excluded. Decreases in dust content are expected in low-metallicity gas above the Galactic plane, resulting from grain destruction in shocks, settling to the disk, and thermal sputtering in hot halo gas.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-10-18T18:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "high galactic latitudes",
      "interstellar gas-to-dust ratios",
      "variations",
      "high latitude",
      "galactic plane"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 37,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}