What controls star formation in the central 500 pc of the Galaxy

By J. Kruijssen, S. Longmore, Bruce G. Elmegreen, N. Murray, J. Bally, L. Testi, R. C. K. J. E. Garching, E. Garching, L. Liverpool, I. T. R. Center and 4 more. 2013

200 citations recorded by the source corpus.

The star formation rate (SFR) in the Central Molecular Zone (CMZ, i.e. the central 500 pc) of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation th eories. In this paper, we quantify which physical mechanisms could be responsible. On scales larger than the disc scale height, the low SFR is found to be consistent with episodic star formation due to secular instabilities or possibly variations of the gas inflow along the Galact ic bar. The CMZ is marginally Toomre-stable when including gas and stars, but highly Toomre-stable when only accounting for the gas, indicating a low condensation rate of self-grav itating clouds. On small scales, we find that the SFR in the CMZ may be caused by an elevated critica l density for star formation due to the high turbulent pressure. The existence of a universal density threshold for star formation is ruled out. The HI‐H2 phase transition of hydrogen, the tidal field, a possible underproduction of massive stars due to a bottom-heavy initial mass function, magnetic fields, and cosmic ray or radiation pressure feedback also cannot individually explain the low SFR. We propose a self-consistent cycle of star formation in the CMZ, in which the effects of several different processes combine to inhibit star formation . The rate-limiting factor is the slow evolution of the gas towards collapse ‐ once star formation is initiated it proceeds at a normal rate. The ubiquity of star formation inhibitors suggests th at a lowered central SFR should be a common phenomenon in other galaxies. We discuss the implications for galactic-scale star formation and supermassive black hole growth, and relate our results to the star formation conditions in other extreme environments.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/5214439504ab8b73d62a6978cf27ac12c7586231

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In Astronomy and Astrophysics

1. Mark R. Krumholz
2. D. Kruijssen
3. J. Kruijssen
4. A. Leroy
5. A. Bolatto
6. S. Longmore
7. T. Pillai
8. P. Hopkins

Citations in the corpus

• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline (2014, methodology): “…a rate below galactic star formation relations (Longmore et al. 2013a),which is likely due to the fact that much of the gas is not self-gravitating (Kruijssen et al. 2014), star formation does proceed at a normal (rapid) rate in the self-gravitating clouds where most of the star formation occurs.”
• Molecular gas kinematics within the central 250 pc of the Milky Way (2016, background): “Gas column and volume densities can be ∼ 2 orders of magnitude greater (Longmore et al. 2013a; Kruijssen et al. 2014; Rathborne et al. 2014b), velocity dispersions measured for a given physical size are larger (e.g. Bally et al. 1988; Shetty et al. 2012), and although there exists a significant…”
• Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies (2015, background): “…rate at young cluster ages (named th ‘cruel cradle effect’ byKruijssen et al. 2011; also seeElmegreen & Hunter 2010) is of key importance during the early phase of GC evolution within the host galaxy disc, particularly in high-pressure environments (e.g.Elmegreen 2010; Kruijssen et al. 2014).”
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, background): “The Galactic CMZ has attracted a great deal of attention recently because it has a much higher ratio of dense gas mass to star formation tracers than the rest of the galaxy (Longmore et al. 2013b, 2012, 2013a; Kruijssen et al. 2014; Yusef-Zadeh et al. 2009; Immer et al. 2012).”
• An uncertainty principle for star formation - I. Why galactic star formation relations break down below a certain spatial scale (2014, methodology): “In a follow-up paper (Kruijssen et al. 2014, hereafter K14), we apply the uncertainty principle to observational dta.”
• Star formation rates and efficiencies in the Galactic Centre (2017, background): “Kruijssen et al. (2014) have suggested that the majority of gas within the CMZ is not bound by self-gravity, rather it is bound by the potential produced from the embedded bulge stars.”
• A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, background): “Even including the central molecular zone, the central few kpc of the Galaxy contain ∼10 per cent of its star formation or ISM mass (e.g. Kruijssen et al. 2014).”
• Cloud-scale Molecular Gas Properties in 15 Nearby Galaxies (2018, background): “This suggests that in these environments, external gravitational potential is at least as important as cloud self-gravity in regulating cloud dynamics (Heyer et al. 2009; Field et al. 2011; Kruijssen et al. 2014).”