Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the Galactic plane
Jul 25, 201313 pages
Published in:
- Astron.Astrophys. 564 (2014) A45
- Published: Apr 4, 2014
e-Print:
- 1307.6815 [astro-ph.GA]
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Abstract: (EDP Sciences)
We use Planck HFI data combined with ancillary radio data to study theemissivity index of the interstellar dust emission in the frequency range 100-353GHz, or3-0.8mm, in the Galactic plane. We analyse the region l = 20deg.-44deg. and |b| where thefree-free emission can be estimated from radio recombination line data. We fit the spectraat each sky pixel with a modified blackbody model and two opacity spectral indices,beta_mm and beta_FIR, below andabove 353GHz, respectively. We find that beta_mm is smaller than beta_FIR, and wedetect a correlation between this low frequency power-law index and the dust optical depthat 353GHz, tau_353. The opacity spectral indexbeta_mm increases from about 1.54 in the morediffuse regions of the Galactic disk, |b| = 3deg.-4deg. and tau_353 ~ 5 x 10^-5, to about1.66 in the densest regions with an optical depth of more than one order of magnitudehigher. We associate this correlation with an evolution of the dust emissivity related tothe fraction of molecular gas along the line of sight. This translates intobeta_mm ~ 1.54 for a medium that ismostly atomic and beta_mm ~ 1.66 when the medium isdominated by molecular gas. We find that both the two-level system model and magneticdipole emission by ferromagnetic particles can explain the results. These results improveour understanding of the physics of interstellar dust and lead towards a complete model ofthe dust spectrum of the Milky Way from far-infrared to millimetre wavelengths.Note:
- 13 pages, 12 figures; accepted for publication in Astronomy and Astrophysics
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