The Hi-GAL compact source catalogue – I. The physical properties of the clumps in the inner Galaxy (−71$_{.}^{\circ}$0 < ℓ < 67$_{.}^{\circ}$0)

Abstract

Hi-GAL is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 µm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogs presented in Molinari et al. (2016a), covering the portion of Galactic plane −71.0 • < < 67.0 • . The band-merged catalogue contains 100922 sources with a regular SED, 24584 of which show a 70 µm counterpart and are thus considered proto-stellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterise different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in proto-stellar sources compared to prestellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to proto-stellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between "on-arm" and "inter-arm" positions.

The evolutionary status of protostellar clumps hosting class II methanol masers

“…The derivation of clump properties for the 6.7 GHz hosts from their FIR fluxes allows us to compare this sample against existing catalogues of high-mass star forming clumps. Within the 22,426 protostellar sources reported by Elia et al (2017), we select the 22,293 sources satisfying the same multi-wavelength (70 to 350 µm) visibility criteria as the maser sample, and restrict to the Galactic longitude and latitude range of the MMB survey. Additionally, we only consider the 25 per cent of the above sources with 'good' distances (i.e.…”

“…Subject to these constraints, 731 6.7 GHz methanol masers (72.5 per cent) are identified with infrared emission in all bands between 70 and 350 µm In addition to these sources, we also note that 22 masers (2.2 per cent) are identified with emission at wavelengths between 160, 250 and 350 µm but lack a detected 70 µm counterpart. Elia et al (2017) show that a deeper targeted extraction at 70 µm towards such sources is likely to reveal a counterpart or provide an upper limit on the flux from any warm component present. By visual inspection of the Hi-GAL maps, we confirm that these maser sources do all have a counterpart at 70 µm but are not recovered by CuTEx.…”

“…In this work, we carry out a multi-wavelength analysis using the CuTEx catalogues to derive the physical properties of massive clumps hosting methanol masers. Elia et al (2017) have derived the properties of the population of massive clumps visible with Hi-GAL and we use their results to provide a sample of objects against which to compare maser-hosting clumps.…”

“…Of the 627 sources falling within the MIPSGAL survey range, only 40.8 per cent of the sample (304 sources) were found to have an associated MIPS-GAL 24 µm point source. As for the 70 µm catalogues, Elia et al (2017) also performed a deeper targeted extraction in the MIPSGAL data towards their protostellar objects to recover faint sources to either identify missing counterparts, or provide an upper limit on the 24 µm flux.…”

“…For this work, the maser clump luminosity is strictly defined as the integral given by the tabulated Hi-GAL data between 70 and 500 µm, and so is a measure of the far-infrared luminosity. On the other hand, Elia et al (2017) calculate the bolometric luminosity of each source by including the flux at wavelengths outside the Hi-GAL wavelength range. For the sources in the protostellar sample with a counterpart detected in either the MIPSGAL, 22 µm WISE or 21 µm MSX (Egan et al 2003) data, the range of fluxes used to calculate source luminosity have been extended to have a lower limit of ∼20 µm.…”