Observational study reveals large-scale interstellar dust temperature gradients across the Milky Way, indicating diffuse atomic clouds dominate far-infrared emission.
Key Points
Characterize the large-scale physical properties of interstellar dust, including temperature, emissivity, and dust-to-gas mass ratios across different gas phases of the Galactic plane.
Analyzed COBE Diffuse Infrared Background Experiment (DIRBE) 140 and 240 μm emission data across the Galactic plane (|b| < 10°).
Combined infrared data with radio surveys tracing molecular (H2), neutral atomic (H I), and extended low-density ionized (H II) interstellar gas phases.
Cold dust (17 to 22 K) associated with diffuse H I clouds accounts for 60% to 75% of Galactic far-infrared luminosity, molecular gas accounts for 15% to 30% (at ~19 K), and extended ionized gas contributes <10% (at ~29 K).
Dust temperatures exhibit significant longitudinal and latitudinal gradients that decrease with increasing Galactocentric distance, differing from IRAS measurements due to transiently heated small dust grains.
The gas-to-dust mass ratio along the line of sight reverses its inward Galactic decrease within 2° of the Galactic center, increasing by a factor of approximately 2 to 3.