Candidate super star cluster progenitor gas clouds possibly triggered by close passage to Sgr A*

Abstract

Super star clusters are the end product of star formation under the most extreme conditions. As such, studying how their final stellar populations are assembled from their natal progenitor gas clouds can provide strong constraints on star formation theories. An obvious place to look for the initial conditions of such extreme stellar clusters are gas clouds of comparable mass and density, with no star formation activity. We present a method to identify such progenitor gas clouds and demonstrate the technique for the gas in the inner few hundred pc of our Galaxy. The method highlights three clouds in the region with similar global physical properties to the previously identified extreme cloud, G0.253+0.016, as potential young massive cluster (YMC) precursors. The fact that four potential YMC progenitor clouds have been identified in the inner 100 pc of the Galaxy, but no clouds with similar properties have been found in the whole first quadrant despite extensive observational efforts, has implications for cluster formation/destruction rates across the Galaxy. We put forward a scenario to explain how such dense gas clouds can arise in the Galactic centre environment, in which YMC formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time.

The Link Between Turbulence, Magnetic Fields, Filaments, and Star Formation in the Central Molecular Zone Cloud G0.253+0.016

“…Anisotropies of this level introduce <40% uncertainties in the 2D-to-3D reconstruction of the density dispersion. 20 Orbital dynamics might also introduce anisotropies (Longmore et al 2013b), but we have not quantified this effect here.…”

Star formation in the Gaia era

“…All these structures are part of a common time sequence of star formation in which GMCs are squeezed as they pass close to the supermassive black hole Sgr A*, inducing star formation within them (Longmore et al, 2013).…”

The Herschel view of the Galactic center

“…The star formation rate (SFR) in the CMZ has been estimated from counts of infrared sources, massive stars, radio free-free emission, masers, and Hii regions and is found to be between 0.02 and 0.1 M yr −1 (Morris & Serabyn 1996;Yusef-Zadeh, et al 2009;Longmore et al 2013a). Dividing the current mass (3 − 7 × 10 7 M ) of the CMZ by the SFR gives a dense-gas depletion time of order τ deplete = 3 × 10 8 to 5 × 10 9 years.…”

“…While 80% of the 1.3 cm NH 3 emission (a tracer of dense gas) in the Milky Way's Galactic plane is in the CMZ, less than 5% of the Milky Way's stars form there (Longmore et al 2013a). Kruijssen et al (2013) explored possible reasons for a depressed star formation rate per unit mass of dense gas.…”