D. Paradis, R. Paladini, A. Noriega-Crespo, C. Mény, F. Piacentini, M. A. Thompson, D. J. Marshall, M. Veneziani, J. -P. Bernard, S. Molinari
Past and recent observations have revealed unexpected variations of the
FIR-mm dust emissivity. In the Herschel spectral range, those are often
referenced to as a 500 {\mu}m emission excess. Several dust emission models
have been developed to interpret astrophysical data in the FIR-mm domain.
However, these are commonly not able to fully reconcile theoretical predictions
with observations. On the contrary, the recently revised Two Level System (TLS)
model seems to provide a promising way to interpret the existing data. The
newly available Herschel Hi-GAL data which covers most of the inner Milky-Way
offers a unique opportunity to investigate possible variations in the dust
emission properties both with wavelength and the environment. By combining the
IRIS 100 {\mu}m with the Hi-GAL 160, 250, 350 and 500 {\mu}m data, we model the
dust emission spectra in each pixel of the Hi-GAL maps, using both the TLS
model and, for comparison, a single modified black-body fit. The effect of
temperature mixing along the line of sight is investigated. We find a slight
decrease in the dust temperature with distance from the Galactic center. We
also report the detection of a significant 500 {\mu}m emissivity excess in the
peripheral regions of the plane (35\circ<|l|<70\circ) of about 13-15% of the
emissivity, that can reach up to 20% in some HII regions . The spatial
distribution of the best-fit values for the two main parameters of the TLS
model, i.e. the charge correlation length, lc, used to characterize the
disordered charge distribution (DCD) part of the model, and the amplitude A of
the TLS processes, with respect to the DCD effect, are shown. They highlight
the plausible existence of an overall gradient with distance to the Galactic
center. Comparison with previous findings in the solar neighborhood shows that
the local value of the excess is less than expected from the Galactic gradient
observed here.
View original:
http://arxiv.org/abs/1111.1852
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