ISM properties in a localized field with the inversion technique. Results from l = 30◦ Hi-GAL field
R. Paladini, A. Noriega-Crespo, S. Molinari, P. Natoli, M. Compiegne, et al.
The Open Time Key project Hi-GAL (Herschel infrared Galactic Plane Survey) has mapped the inner Galaxy in the coordinates range |l| ≤ 60°, |b| ≤ 1°, and for wavelengths from 70 to 500 μm. Using both the PACS and SPIRE instruments, Hi-GAL has detected cold structures and thousands of star formation regions. The recent release of these high-resolution data also allows detailed investigations of the properties of the Interstellar Medium (ISM). In this talk, we present the results obtained from the study of the Galactic ISM in a 2×2 square degree region corresponding to one of the Hi-GAL Science Demonstration fields, centered on (l, b) = (30, 0). This field encompasses the tangent point to the Scutum-Crux spiral arm, and identifies a region, in Galactocentric radii, between 4.25 and 5.6 kpc. Using an inversion technique, we have isolated the dust emission which originates from this region. Combining the Hi-GAL data with the velocity information provided by gas tracers of hydrogen in the atomic (HI), molecular (H2) and ionized phase (H+), we have disentangled - at each wavelength - the dust emission associated to the gas in these different regimes. As well as to the Hi-GAL data, we have applied the inversion technique to the MIPSGAL 24 μm and GLIMPSE 8 μm. The synergy between the Hi-Gal far-infrared data and the mid- and near-infrared data from MIPSGAL/GLIMPSE, allow us to probe all known populations of dust grains, i.e. from the Big Grains (BGs) to the Very Small Grains (VSGs) and Polycyclic Aromatic Hydrocarbons (PAHs). We have used the DUSTEM model (Compiegne et al. 2011) to build and interpret the Spectral Energy Distributions (SEDs) for dust in the atomic, molecular and ionized gas phase. We found dust temperatures of, respectively, T(HI)=19.52±0.71 K, T(H2)=19.91±1.51 K and T(H+) =23.15±1.02 K, and an indication of PAH depletion for the ionized gas phase, as previously observed in other regions of our Galaxy and in the LMC.