Observation of TeV gamma ray extended sources with ARGO-YBJ

More than 80% of TeV galactic gamma ray sources are spatially extended and many of them are still unidentified. The extended emission could be the result of cosmic ray interactions with the ambient medium which provides the target to produce TeV gamma rays. The sensitivity of ground based gamma ray detectors decreases for extended sources; shower detectors, due to their large field of view, are less affected with respect to Cherenkov telescopes. The ARGO-YBJ experiment (Yangbajing Cosmic Ray Laboratory, Tibet, China, 4300 m of altitude) is an air shower detector devoted to gamma ray astronomy at energies above a few hundred GeV, with an integrated sensitivity ranging from 0.24 to ~ 1 Crab units, depending on the source declination. In this paper the observation of galactic extended sources with ARGO-YBJ during 5 years is reviewed.