Variations of Interstellar Gas-to-dust Ratios at High Galactic Latitudes
Artikel i vetenskaplig tidskrift, 2024

Interstellar dust at high Galactic latitudes can influence astronomical foreground subtraction, produce diffuse scattered light, and soften the UV spectra of quasars. In a sample of 94 sight lines toward quasars at high latitude and low extinction, we evaluate the interstellar “gas-to-dust ratio” N H/E(B − V), using hydrogen column densities (H i and H2) and far-IR (FIR) estimates of dust reddening. In the Galactic plane, this ratio is 6.0 ± 0.2 (in units of 1021 cm−2 mag−1). On average, recent Planck estimates of E(B − V) in low-reddening sight lines are 12% higher than those from Schlafly & Finkbeiner, and N H I exhibits significant variations when measured at different radio telescopes. In a sample of 51 quasars with measurements of both H i and H2 and 0.01 ≤ E(B − V) ≲ 0.1, we find mean ratios 10.3 ± 0.4 (gas at all velocities) and 9.2 ± 0.3 (low-velocity only) using Planck E(B − V) data. High-latitude H2 fractions are generally small (2%-3% on average), although nine of 39 sight lines at ∣b∣ ≥ 40° have f H2 of 1%-17%. Because FIR-inferred E(B − V) is sensitive to modeled dust temperature T d and emissivity index β, 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 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.

Författare

J. Michael Shull

University of Colorado at Boulder

Georgia Virginia Panopoulou

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 961 2 204

Ämneskategorier

Astronomi, astrofysik och kosmologi

DOI

10.3847/1538-4357/ad0f20

Mer information

Senast uppdaterat

2024-02-09