A Herschel and BIMA study of the sequential star formation near the 48A HII region

We present the results of Herschel HOBYS (Herschel imaging survey of OB Young Stellar objects) photometricmapping combined with Berkeley Illinois Maryland Association (BIMA) observations and additional archival data, and perform an in-depth study of the evolutionary phases of the star-forming clumps in W 48A and their surroundings. Age estimates for the compact sources were derived from bolometric luminosities and envelope masses, which were obtained from the dust continuum emission, and agree within an order of magnitude with age estimates from molecular line and radio data. The clumps in W 48A are linearly aligned by age (east-old to west-young): we find a ultra-compact (UC) HII region, a young stellar object (YSO) with class II methanol maser emission, a YSO with a massive outflow and finally the NH2D prestellar cores from Pillai et al. This remarkable positioning reflects the (star) formation history of the region. We find that it is unlikely that the star formation in the W48A molecular cloud was triggered by the UC HII region and discuss the Aquila supershell expansion as a major influence on the evolution of W48A. We conclude that the combination of Herschel continuum data with interferometric molecular line and radio continuum data is important to derive trustworthy age estimates and interpret the origin of large-scale structures through kinematic information. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.