Star formation triggered by HII regions in our Galaxy: First results for
  N49 from the Herschel infrared survey of the Galactic plane
  It has been shown that by means of different physical mechanisms the
expansion of HII regions can trigger the formation of new stars of all masses.
This process may be important to the formation of massive stars but has never
been quantified in the Galaxy. We use Herschel-PACS and -SPIRE images from the
Herschel Infrared survey of the Galactic plane, Hi-GAL, to perform this study.
We combine the Spitzer-GLIMPSE and -MIPSGAL, radio-continuum and sub-millimeter
surveys such as ATLASGAL with Hi-GAL to study Young Stellar Objects (YSOs)
observed towards Galactic HII regions. We select a representative HII region,
N49, located in the field centered on l=30 degr observed as part of the Hi-GAL
Science Demonstration Phase, to demonstrate the importance Hi-GAL will have to
this field of research. Hi-GAL PACS and SPIRE images reveal a new population of
embedded young stars, coincident with bright ATLASGAL condensations. The Hi-GAL
images also allow us, for the first time, to constrain the physical properties
of the newly formed stars by means of fits to their spectral energy
distribution. Massive young stellar objects are observed at the borders of the
N49 region and represent second generation massive stars whose formation has
been triggered by the expansion of the ionized region. Hi-GAL enables us to
detect a population of young stars at different evolutionary stages, cold
condensations only being detected in the SPIRE wavelength range. The far IR
coverage of Hi-GAL strongly constrains the physical properties of the YSOs. The
large and unbiased spatial coverage of this survey offers us a unique
opportunity to lead, for the first time, a global study of star formation
triggered by HII regions in our Galaxy.
