2017A&A...599A.139K

Context. Massive-star formation and the processes involved are still poorly understood. The ATLASGAL survey provides an ideal basis for detailed studies of large numbers of massive-star forming clumps covering the whole range of evolutionary stages. The ATLASGAL Top100 is a sample of clumps selected by their infrared and radio properties to be representative for the whole range of evolutionary stages.
Aims. The ATLASGAL Top100 sources are the focus of a number of detailed follow-up studies that will be presented in a series of papers. In the present work we use the dust continuum emission to constrain the physical properties of this sample and identify trends as a function of source evolution.
Methods. We determine flux densities from mid-infrared to submillimeter wavelength (8-870µm) images and use these values to fit their spectral energy distributions and determine their dust temperature and flux. Combining these with recent distances from the literature including maser parallax measurements we determine clump masses, luminosities and column densities.
Results. We define four distinct source classes from the available continuum data and arrange these into an evolutionary sequence. This begins with sources found to be dark at 70µm, followed by 24µm weak sources with an embedded 70µm source, continues through mid-infrared bright sources and ends with infrared bright sources associated with radio emission (i.e., HII regions). We find trends for increasing temperature, luminosity, and column density with the proposed evolution sequence, confirming that this sample is representative of different evolutionary stages of massive star formation. Our sources span temperatures from approximately 11 to 41K, with bolometric luminosities in the range 57L_☉-3.8x10⁶L_☉. The highest masses reach 4.3x10⁴M_☉ and peak column densities up to 1.1x10²⁴cm^–1, and therefore have the potential to form the most massive O-type stars. We show that at least 93 sources (85%) of this sample have the ability to form massive stars and that most are gravitationally unstable and hence likely to be collapsing.
Conclusions. The highest column density ATLASGAL sources cover the whole range of evolutionary stages from the youngest to the most evolved high-mass-star forming clumps. Study of these clumps provides a unique starting point for more in-depth research on massive-star formation in four distinct evolutionary stages whose well defined physical parameters afford more detailed studies. As most of the sample is closer than 5 kpc, these sources are also ideal for follow-up observations with high spatial resolution.