Physical properties of high-mass clumps in different stages of evolution

Abstract

Context. The details of the process of massive star formation are still elusive. A complete characterization of the first stages of the process from an observational point of view is needed to constrain theories on the subject. In the past 20 years we have made a thorough investigation of colour-selected IRAS sources over the whole sky. The sources in the northern hemisphere were studied in detail and used to derive an evolutionary sequence based on their spectral energy distribution. Aims. To investigate the first stages of the process of high-mass star formation, we selected a sample of massive clumps previously observed with the Swedish-ESO Submillimetre Telescope at 1.2 mm and with the ATNF Australia Telescope Compact Array at 1.3 cm. We want to characterize the physical conditions in such sources, and test whether their properties depend on the evolutionary stage of the clump. Methods. With ATCA we observed the selected sources in the NH 3 (1, 1) and (2, 2) transitions and in the H 2 O(6 16 −5 23 ) maser line. Ammonia lines are a very good temperature probe that allow us to accurately determine the mass and the column, volume, and surface densities of the clumps. We also collected all data available to construct the spectral energy distribution of the individual clumps and to determine if star formation is already occurring through observations of its most common signposts, thus putting constraints on the evolutionary stage of the source. We fitted the spectral energy distribution between 1.2 mm and 70 µm with a modified black body to derive the dust temperature and independently determine the mass. Results. We find that the clumps are cold (T ∼ 10−30 K), massive (M ∼ 10 2 −10 3 M ), and dense (n(H 2 ) 10 5 cm −3 ) and that they have high column densities (N(H 2 ) ∼ 10 23 cm −2 ). All clumps appear to be potentially able to form high-mass stars. The most massive clumps appear to be gravitationally unstable, if the only sources of support against collapse are turbulence and thermal pressure, which possibly indicates that the magnetic field is important in stabilizing them. Conclusions. After investigating how the average properties depend on the evolutionary phase of the source, we find that the temperature and central density progressively increase with time. Sources likely hosting a ZAMS star show a steeper radial dependence of the volume density and tend to be more compact than starless clumps.

Magnetically regulated fragmentation of a massive, dense, and turbulent clump

“…We have simulated the gravitational collapse of I16061c1 through 3D numerical simulations following Commerçon et al (2011), adopting a mass, temperature, average density, and level of turbulence of the parent clump very similar to those measured (Beltrán et al 2006;Giannetti et al 2013). In particular, the Mach number setting the initial turbulence was derived from the line width of C 18 O (3−2) by Fontani et al (2012).…”

“…We adopted T d = 25 K, corresponding to the gas temperature derived by Giannetti et al (2013), assuming coupling between gas and dust (reasonable assumption at the high average density of the clump). The dust mass opacity coefficient was derived from the equation κ ν = κ ν 0 (ν/ν 0 ) β .…”

The almost ubiquitous association of 6.7-GHz methanol masers with dust★

“…L bol/mmb /M clump is therefore expected to increase as the embedded source evolves towards the main sequence. This model has been reasonably successful in tracing the evolution of massive protostars (e.g., Molinari et al 2008;Giannetti et al 2013;Urquhart et al 2014c).…”

High-Mass Star Formation Toward Southern Infrared Bubble S10

“…Apart from this, rest of the clumps do not reveal any signposts of active star formation. Following the discussion in Molinari et al (2008) and Giannetti et al (2013), these could be regarded as either being starless or with a deeply embedded ZAMS star. All clumps in our sample have luminosities, L > 10 3 L ⊙ and hence are likely to host ZAMS stars (Giannetti et al 2013).…”