Abstract
The association of very-high energy (VHE; E > 100GeV) sources with regions of the sky rich in dust and gas has been noticed in the study of individual VHE sources. However, the statistical significance of this correlation for the whole population of TeV detections has not been assessed yet. To trace the material content, we make use of the publicly released all-sky maps of astrophysical foregrounds of the Planck Collaboration, and of an extensive existing CO mapping of the Galactic sky. To test the correlation, we construct randomized samples of VHE source positions starting from the inner Galactic plane survey. A positive correlation cannot be firmly established yet. Additionally we explore the possibility that unidentified VHE sources are located in environment particularly rich in material content unaccounted by traditional tracers, including HI hyperfine transition at 21cm to trace atomic hydrogen in regions where the gas is diffuse. No additional gas component is found in the direction of unidentified VHE sources.
Highlights
Most of the very-high energy (VHE; E 100 GeV) galactic sources were discovered in the last decade through a scan of the Galactic plane region by the High Energy Stereoscopic System (H.E.S.S.)
We explore the possibility that unidentified VHE sources are located in environment rich in material content unaccounted by traditional tracers, including HI hyperfine transition at 21 cm to trace atomic hydrogen in regions where the gas is diffuse
The final proof of correlation is left for the future, when the forthcoming Cherenkov Telescope Array (CTA) observations will provide us with more sources (Dubus et al 2013)
Summary
Most of the very-high energy (VHE; E 100 GeV) galactic sources were discovered in the last decade through a scan of the Galactic plane region by the High Energy Stereoscopic System (H.E.S.S.). It would seem that the Galactic VHE sources are in regions of the sky where the surrounding is rich in molecular material, but no correlation is established up to date Such a relation would be expected in a scenario where the VHE emission has an hadronic origin: the accelerated cosmic rays (CRs, protons or heavier nuclei) interact with the surrounding material, leading to VHE emission through the decay of the produced π 0 (Ginzburg & Syrovatskii 1964). VHE emission has been predicted to be produced in regions of massive-star formation, where apart from being obvious sites prone to the appearance of SNRs and other accelerators, the strong winds of the hot OB stars in the clusters form acceleration regions at wind interaction zones These regions are rich in molecular material and dust and are expected to be bright regions for the tracers that we consider here. The work presented here is part of works published previously in Pedaletti et al ( 2014) and Pedaletti et al ( 2015)
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