Clouds, filaments, and protostars: TheHerschel Hi-GAL Milky Way

Abstract

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key program that will map the inner Galactic plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2 • × 2 • tiles approximately centered at l = 30 • and l = 59 • . The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around A V ∼ 1 is exceeded for the regions in the l = 59 • field; a A V value between 5 and 10 is found for the l = 30 • field, likely due to the relatively higher distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm −2 . Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.

Cloud Structure of Three Galactic Infrared Dark Star-forming Regions from Combining Ground- and Space-based Bolometric Observations

“…(Program ID is M11BEC30 for G11.11−0.12 and G28.34+0.06.) Ancillary data also includes level 2.5 and level 3 processed, archival Herschel 16 images, which were taken by the Herschel Infrared Galactic Plane (Hi-GAL) survey (Molinari et al 2010) at 70/160 μm using the PACS instrument (Poglitsch et al 2010) and at 250/350/500 μm using the SPIRE instrument (Griffin et al 2010). Observation IDs for G14.225−0.506 are 1342218997 and 1342219000, for G11.11−0.12 theyare 1342204952 and1342218965, and for G28.34+0.06 it is 1342218694.…”

High-mass Star Formation through Filamentary Collapse and Clump-fed Accretion in G22

“…Prevalent filaments detected in our Galaxy are wellestablished as some of the main sites for star formation (André et al 2010Molinari et al 2010a;Wang et al 2014Wang et al , 2015Wang et al , 2016. Specifically, hub-filament systems are frequently reported forming high-mass stars (e.g., Hennemann et al 2012;Liu et al 2012Liu et al , 2016Peretto et al 2013).…”

Absorption Filaments Toward the Massive Clump G0.253+0.016

“…Fitting the dust continuum spectral energy distribution to the Herschel 60, 160,250,350, and 500 μm data obtained from the Herschel Space Observatory Hi-GAL survey (Molinari et al 2011(Molinari et al , 2010a(Molinari et al , 2010b and 1100 μm from the Bolocam Galactic Plane Survey (Bally et al 2010) reveals a dust temperature of ∼20 K, H 2 column density of ∼3.3 × 10 23 cm −2 , and mass of ∼10 5 M (Longmore et al 2012(Longmore et al , 2013. Absorption in the near-and farinfrared and application of the virial theorem to spectral line data (Rathborne et al 2014b) give similar results for the mass and column density.…”