Star Formation in the Central Molecular Zone of the Milky Way

Henshaw, Jonathan D.; Barnes, Ashley T.; Battersby, Cara; Ginsburg, Adam; Sormani, Mattia C.; Walker, Daniel

doi:10.48550/arxiv.2203.11223

Cited by 33 publications

(41 citation statements)

References 122 publications

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“…Weiß et al (2001) provided a multi-transition analysis of the molecular gas and showed the regions of most violent star formation are confined to the molecular lobes, and are arranged in a toroidal topology around the nucleus. Star-forming rings are also observed in the nearby starburst NGC 253 (Arnaboldi et al 1995;Leroy et al 2018), other local galaxies (see Buta & Crocker 1993;Böker et al 2008;Comerón et al 2010;Leroy et al 2021), and the Milky Way galaxy (see Henshaw et al 2022).…”

Section: Introductionmentioning

confidence: 87%

Galactic winds and bubbles from nuclear starburst rings

Nguyen¹,

Thompson²

2022

Preprint

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Galactic outflows from local starburst galaxies typically exhibit a layered geometry, with cool 10 4 K flow sheathing a hotter 10 7 K, cylindrically-collimated, X-ray emitting plasma. Here, we argue that winds driven by energy-injection in a ring-like geometry can produce this distinctive large-scale multi-phase morphology. The ring configuration is motivated by the observation that massive young star clusters are often distributed in a ring at the host galaxy's inner Lindblad resonance, where larger-scale spiral arm structure terminates. We present parameterized three-dimensional radiative hydrodynamical simulations that follow the emergence and dynamics of energy-driven hot winds from starburst rings. We show that the flow shocks on itself within the inner ring hole, maintaining high 10 7 K temperatures, whilst flows that emerge from the wind-driving ring unobstructed can undergo rapid bulk cooling down to 10 4 K, producing a fast hot bi-conical outflow enclosed by a sheath of cooler nearly co-moving material. The hot flow is collimated along the ring axis, even in the absence of pressure confinement from a galactic disk or magnetic fields. In the early stages of expansion, the emerging wind forms a bubble-like shape reminiscent of the Milky Way's eROSITA and Fermi bubbles. The bubble is preceded by a fast transient flow along the minor axis that can reach velocities usually associated with AGN-driven winds ( 3000 − 10000 km s −1 ), depending on the density of the surrounding medium. We discuss the physics of the ring configuration, the conditions for radiative bulk cooling, and the implications for future X-ray observations.

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Section: Introductionmentioning

confidence: 87%

Galactic winds and bubbles from nuclear starburst rings

Nguyen¹,

Thompson²

2022

Preprint

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“…Hatchfield et al (2021) find that simulated CMZ clouds have peaks in their average density at the point where they collide violently with inflowing material. However, it is unlikely that the collision observed in cloud 'd' is is driven by bar inflow, as cloud 'd' is not located near any proposed entry point to the CMZ (Henshaw et al 2022a). It is also extremely unlikely that cloud 'd' is a collision occurring downstream from an entry point, as the collision is currently ongoing.…”

Section: Source Of Converging Flowsmentioning

confidence: 99%

“…Bressert et al 2012;Ginsburg et al 2012;Urquhart et al 2013;Longmore et al 2013aLongmore et al , 2017, such clouds have remained elusive in the Milky Way. The most promising examples to date have generally been found in the 'Central Molecular Zone' (CMZ) -the inner few hundred pc of the Galaxy (Henshaw et al 2022a) (the Henshaw+22 reference has been added in this edit). In particular, a region of the CMZ known as the 'dust ridge' (Lis et al 1994), contains a collection of six massive (10 5 M ), compact (radius ∼1-3 pc), and largely quiescent clouds (excluding the Sagittarius B2 complex, one of the most active sites of high-mass star formation in the entire Milky Way, e.g.…”

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confidence: 99%

The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows

Williams,

Walker,

Longmore

et al. 2022

Preprint

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Young massive clusters (YMCs) are compact ( 1 pc), high-mass (>10 4 M ) stellar systems of significant scientific interest. Due to their rarity and rapid formation, we have very few examples of YMC progenitor gas clouds before star formation has begun. As a result, the initial conditions required for YMC formation are uncertain. We present high-resolution (0.13 , ∼1000 au) ALMA observations and Mopra single-dish data, showing that Galactic Centre dust ridge 'Cloud d' (G0.412+0.052, mass = 7.6 × 10 4 M , radius = 3.2 pc) has the potential to become an Arches-like YMC (10 4 M , r ∼ 1 pc), but is not yet forming stars. This would mean it is the youngest known pre-star forming massive cluster and therefore could be an ideal laboratory for studying the initial conditions of YMC formation. We find 96 sources in the dust continuum, with masses 3 M and radii of ∼10 3 au. The source masses and separations are more consistent with thermal rather than turbulent fragmentation. It is not possible to unambiguously determine the dynamical state of most of the sources, as the uncertainty on virial parameter estimates is large. We find evidence for large-scale (∼1 pc) converging gas flows, which could cause the cloud to grow rapidly, gaining 10 4 M within 10 5 yr. The highest density gas is found at the convergent point of the large-scale flows. We expect this cloud to form many high-mass stars, but find no high-mass starless cores. If the sources represent the initial conditions for star formation, the resulting IMF will be bottom-heavy.

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“…2 We normalize the IMF so that 0.15 so that m ∼ 0.5), and a Ṁ * ∼ 0.1 (e.g. Henshaw et al 2022 and references therein) we obtain Ėkin,winds ∼ 10 40 erg/s for the entire volume of the CMZ to which the star formation estimate refers. Converting this to a per-volume estimate is not trivial.…”

Section: Energy Deposition By Stellar Winds In the Cmzmentioning

confidence: 99%

“…Converting this to a per-volume estimate is not trivial. First, the star formation is not uniformly distributed over the CMZ volume, as is clear from Henshaw et al (2022), who compare different estimates of Ṁ * in the CMZ using different tracers and studying different volumes: as can be seen in their Table 1, there is no strong correlation between the volume of the CMZ studied and the derived value of Ṁ * , which is to be expected if the star formation, massive stars, and molecular clouds are all spatially correlated and only cover a small fraction of the CMZ volume. If we assume that most of this star formation takes place in the same region of the central CMZ covered by the clouds studied in Kauffmann et al (2017a) (radius of ∼ 100 pc, height of ∼ ±5 pc from the Galactic plane), then we obtain Ėkin,winds ∼ 4 × 10 34 erg s −1 pc −3 (corresponding to a population of about 1500 O and B stars of all evolutionary stages within the CMZ).…”

Section: Energy Deposition By Stellar Winds In the Cmzmentioning

confidence: 99%

Dancing with the stars: Stirring up extraordinary turbulence in Galactic center clouds

Tassis,

Pavlidou

2022

Preprint

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Context. Molecular clouds in the central molecular zone (CMZ) have been observed to feature turbulent line widths that are significantly higher, and scale with cloud size more steeply, than in the rest of the Milky Way. In the same Galactic region, the stellar density is also much higher than in the rest of the Milky Way, and the vertical stellar velocity dispersion is large, meaning that even young stars are likely to cross the entire vertical extent of the CMZ within their lifetimes. Aims. We investigate whether interactions of CMZ molecular clouds with crossing stars can account for the extraordinary properties of observed turbulence in this part of the Galaxy. Methods. We calculated the rate of energy deposition by stars crossing CMZ clouds due to (a) stellar winds and (b) dynamical friction, and compared it to the rate of turbulence decay. We calculated the predicted scaling of turbulence line width with cloud size in each case.Results. We find that energy deposition by stellar winds of crossing massive stars can account for both the level and the scaling of CMZ cloud turbulence with cloud size. We also find that the mechanism stops being effective at a Galactocentric distance comparable to the CMZ extent. On the other hand, we find that dynamical friction by crossing stars does not constitute a significant driver of turbulence for CMZ clouds.

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Star Formation in the Central Molecular Zone of the Milky Way

Cited by 33 publications

References 122 publications

Galactic winds and bubbles from nuclear starburst rings

Galactic winds and bubbles from nuclear starburst rings

The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows

Dancing with the stars: Stirring up extraordinary turbulence in Galactic center clouds

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