On the possible correlation of Galactic very-high energy source locations and enhancements of the surface density in the Galactic plane

¹ Institut de Ciències de l’Espai (IEEC-CSIC), Campus UAB, Torre C5, 2a planta, 08193 Barcelona, Spain
e-mail: gpedalet@ieec.uab.es
² Institució Catalana de Recerca i Estudis Avançats (ICREA), 23, 08010 Barcelona, Spain

Received: 29 November 2013
Accepted: 10 March 2014

Abstract

Aims. The association of very-high energy sources with regions of the sky rich in dust and gas has been noticed in the study of individual very-high energy (VHE; E ≳ 100 GeV) sources. However, the statistical significance of this correlation for the whole population of TeV detections has not been assessed yet. Here, we present a study of the association of VHE sources in the central Galactic region with positions of enhanced material content.

Methods. We obtain estimates of the material content through two classical tracers: dust emission and intensity of the ¹²CO(1 → 0) line. We make use of the recently 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 sources detected by the High Energy Stereoscopic System (H.E.S.S.) array.

Results. We find hints of a positive correlation between positions of VHE sources and regions rich in molecular material, which reaches the 3.9σ level in the best of cases. The latter confidence is however decreased if variations in the selection criteria are considered, which lead us to conclude that a positive correlation cannot be firmly established yet. Forthcoming VHE facilities will be needed to firmly establish the correlation.