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
Rygl, K. L. J.; Schneider, N.; Benedettini, M.; Elia, D.; Pezzuto, S.; Schisano, E.; Fukui, Y.; Onishi, T.; Polychroni, D.; Molinari, S.; Veneziani, M.; Olmi, L.; Maruccia, Y.; Pestalozzi, M.; di Giorgio, A. M.; Yamamoto, H.; Hayakawa, T.; Ikhenaode, D.; Piazzo, L.; Mizuno, A.
Italy, Japan, United States, Puerto Rico, France, Greece
Abstract
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)vpropM -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.