The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline

By J. Kruijssen, J. Dale, S. N. L. M. Garching, Excellence Cluster Universe Garching, Usm Munich, L. Liverpool. 2014

192 citations recorded by the source corpus.

We recently proposed that the star-forming potential of dense molecular clouds in the Central Molecular Zone (CMZ, i.e. the central few 100 pc) of the Milky Way is intimately linked to their orbital dynamics, potentially giving rise to an absolute-time sequence of star-forming clouds. In this paper, we present an orbital model for the gas stream(s) observed in the CMZ. The model is obtained by integrating orbits in the empirically constrained gravitational potential and represents a good fit (⁠χ2red=2.0⁠) to the observed position–velocity distribution of dense (n > several 103 cm-3) gas, reproducing all of its key properties. The orbit is also consistent with observational constraints not included in the fitting process, such as the 3D space velocities of Sgr B2 and the Arches and Quintuplet clusters. It differs from previous, parametric models in several respects: (1) the orbit is open rather than closed due to the extended mass distribution in the CMZ, (2) its orbital velocity (100–200 km s-1) is twice as high as in previous models, and (3) Sgr A* coincides with the focus of the (eccentric) orbit rather than being offset. Our orbital solution supports the recently proposed scenario in which the dust ridge between G0.253+0.016 (‘the Brick’) and Sgr B2 represents an absolute-time sequence of star-forming clouds, of which the condensation was triggered by the tidal compression during their most recent pericentre passage. We position the clouds on a common timeline and find that their pericentre passages occurred 0.30–0.74 Myr ago. Given their short free-fall times (tff ∼ 0.34 Myr), the quiescent cloud G0.253+0.016 and the vigorously star-forming complex Sgr B2 are separated by a single free-fall time of evolution, implying that star formation proceeds rapidly once collapse has been initiated. We provide the complete orbital solution, as well as several quantitative predictions of our model (e.g. proper motions and the positions of star formation ‘hotspots’). The paper is concluded with a discussion of the assumptions and possible caveats, as well as the position of the model in the Galactic context, highlighting its relation to large-scale gas accretion, the dynamics of the bar, the x2 orbital family, and the origin of the Arches and Quintuplet clusters.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/8c926d760a3333ae969472a966c48e337623a1c6

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Citations in the corpus

The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, background): “These velocities fall within the range of typical expansion velocities found in nearby HII regions in the Milky Way, LMC, NGC300, and M33 (6−30 km s−1, see e.g. Bertoldi & McKee 1990; Murray & Rahman 2010; Hygate et al. 2019a; Kruijssen et al. 2019; McLeod et al. 2019b,a) and in numerical simulation”
Star formation rates and efficiencies in the Galactic Centre (2017, methodology): “In the orbital model of Kruijssen et al. (2015), the ‘Brick’ and Sgr B2 are separated by a time along the orbit that is similar to the free-fall time of the ‘Brick’ (see Tables 4 and 5), and thus the comparison for these regions should be robust.”
Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, methodology): “Figure 14 shows the orbital fit from Kruijssen et al. (2015) and a position-velocity slice through the fitted temperature cube following that orbit.”
Molecular gas kinematics within the central 250 pc of the Milky Way (2016, methodology): “As such, our results go further than the notion of a “discontinuity” as described by Kruijssen et al. (2015) (see their Figure 2, bottom panel).”