ATLASGAL – Kinematic distances and the dense gas mass distribution of the inner Galaxy

Abstract

Context. The formation of high mass stars and clusters occurs in giant molecular clouds. Objects in evolved stages of massive star formation such as protostars, hot molecular cores, and ultracompact HII regions have been studied in more detail than earlier, colder objects. Further progress thus requires the analysis of the time before massive protostellar objects can be probed by their infrared emission. With this in mind, the APEX Telescope Large Area Survey of the whole inner Galactic plane at 870 μm (ATLASGAL) has been carried out to provide a global view of cold dust and star formation at submillimetre wavelengths. Aims. We derive kinematic distances to a large sample of massive cold dust clumps from their measured line velocities. We estimate masses and sizes of ATLASGAL sources, for which the kinematic distance ambiguity is resolved. Methods. The ATLASGAL sample is divided into groups of sources, which are located close together, mostly within a radius of 2 pc, and have velocities in a similar range with a median velocity dispersion of ∼1 km s −1 . We use NH 3 , N 2 H + , and CS velocities to calculate near and far kinematic distances to those groups. Results. We obtain 296 groups of ATLASGAL sources in the first quadrant and 393 groups in the fourth quadrant, which are coherent in space and velocity. We analyse HI self-absorption and HI absorption to resolve the kinematic distance ambiguity to 689 complexes of submm clumps. They are associated with 12 CO emission probing large-scale structure and 13 CO (1-0) line as well as the 870 μm dust continuum on a smaller scale. We obtain a scale height of ∼28±2 pc and displacement below the Galactic midplane of ∼−7±1 pc. Within distances from 2 to 18 kpc ATLASGAL clumps have a broad range of gas masses with a median of 1050 M as well as a wide distribution of radii with a median of 0.4 pc. Their distribution in galactocentric radii is correlated with spiral arms. Conclusions. Using a statistically significant ATLASGAL sample we derive a power-law exponent of −2.2 ± 0.1 of the clump mass function. This is consistent with the slope derived for clusters and with that of the stellar initial mass function. Examining the power-law index for different galactocentric distances and various source samples shows that it is independent of environment and evolutionary phase. Fitting the mass-size relationship by a power law gives a slope of 1.76 ± 0.01 for cold sources such as IRDCs and warm clumps associated with HII regions.

Characterizing the properties of cluster precursors in the MALT90 survey

“…located at a far kinematic distance of 10 kpc (Whitaker et al, submitted). Wienen et al (2015) located this clump at its near kinematic distance of ∼4 kpc. If we locate this clumps at this distance, then, it would have a mass of 6.6 ± 0.8 × 10 3 M , a density of 3.9 ± 0.3 × 10 4 cm −3 , and a dust bolometric luminosity of 4.9±0.9 × 10 3 L .…”

“…This average velocity was denominated as consensus velocity of the clump (see Rathborne et al 2016). Near and far kinematic distance disambiguation was determined using the H I absorption/emission (e.g., Kolpak et al 2003;Green & McClure-Griffiths 2011;Wienen et al 2015). No distances were obtained for clumps within the galactic longitude range 350 • < l < 15 • .…”

ALMA survey of massive cluster progenitors from ATLASGAL

“…A combination of turbulence, magnetic field, and radiative feedback could increase the necessary mass scale for (18) a turbulent line width of ∆v obs > ∼ 6 km s −1 at the surface of cores, which is a factor of two higher than the average ∆v obs at the clump scale (Wienen et al 2015). The magnetic critical mass at the average clump density corresponds to M mag < 400 M at the typically observed magnetic field values of 1 mG towards massive clumps (e.g.…”

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

“…To resolve these kinematic distance ambiguities, we have used the Hi self-absorption method (HiSA; e.g. Jackson et al 2002;Roman-Duval et al 2009;Wienen et al 2015). This works on the premise that the cold Hi associated with a source at the near distance will produce a dip in the warmer Hi emission, which arises from warm gas located throughout the Galactic mid-plane, at the same velocity as the source (see Fig.…”

“…). However, for 35 clumps, the multiple components have similar intensities; for these we have either searched the literature for a velocity determined using other high-density tracers, such as NH 3 (1,1) or N 2 H + (1-0) (Jackson et al 2013;Urquhart et al 2014b;Wienen et al 2015), or compared the integrated 13 CO(2 -1) maps of the different velocity components with the ATLASGAL dust emission maps, choosing the velocity component that peaks at the position of the dust emission and where the best correlation between spatial distribution of gas and dust is found (see Fig. 17 for an example of this method).…”