The first hi-gal observations of the outer galaxy: A look at star formation in the third galactic quadrant in the longitude range 216.°5 ≲ ℓ ≲ 225.°5

We present the first Herschel PACS and SPIRE photometric observations in a portion of the outer Galaxy (216.°5 ≲ ℓ ≲ 225.°5 and -2° ≲ b ≲ 0°) as a part of the Hi-GAL survey. The maps between 70 and 500 μm, the derived column density and temperature maps, and the compact source catalog are presented. NANTEN CO(1-0) line observations are used to derive cloud kinematics and distances so that we can estimate distance-dependent physical parameters of the compact sources (cores and clumps) having a reliable spectral energy distribution that we separate into 255 proto-stellar and 688 starless sources. Both typologies are found in association with all the distance components observed in the field, up to 5.8 kpc, testifying to the presence of star formation beyond the Perseus arm at these longitudes. Selecting the starless gravitationally bound sources, we identify 590 pre-stellar candidates. Several sources of both proto- and pre-stellar nature are found to exceed the minimum requirement for being compatible with massive star formation based on the mass-radius relation. For the pre-stellar sources belonging to the Local arm (d ≲ 1.5 kpc) we study the mass function whose high-mass end shows a power law N(log M)M -1.0 ± 0.2. Finally, we use a luminosity versus mass diagram to infer the evolutionary status of the sources, finding that most of the proto-stellar sources are in the early accretion phase (with some cases compatible with a Class I stage), while for pre-stellar sources, in general, accretion has not yet started. © 2013. The American Astronomical Society. All rights reserved.