Modelling CO formation in the turbulent interstellar medium

By S. Glover, Christoph Federrath, M. Mac Low, Ralf Klessen. 2009

274 citations recorded by the source corpus.

We present results from high-resolution three-dimensional simulations of turbulent interstellar gas that self-consistently follow its coupled thermal, chemical and dynamical evolution, with a particular focus on the formation and destruction of H 2 and CO. We quantify the formation time-scales for H 2 and CO in physical conditions corresponding to those found in nearby giant molecular clouds, and show that both species form rapidly, with chemical time-scales that are comparable to the dynamical time-scale of the gas. We also investigate the spatial distributions of H 2 and CO, and how they relate to the underlying gas distribution. We show that H 2 is a good tracer of the gas distribution, but that the relationship between CO abundance and gas density is more complex. The CO abundance is not well-correlated with either the gas number density n or the visual extinction Av : both have a large influence on the CO abundance, but the inhomogeneous nature of the density field produced by the turbulence means that n and A v are only poorly correlated. There is a large scatter in A v , and hence CO abundance, for gas with any particular density, and similarly a large scatter in density and CO abundance for gas with any particular visual extinction. This will have important consequences for the interpretation of the CO emission observed from real molecular clouds. Finally, we also examine the temperature structure of the simulated gas. We show that the molecular gas is not isothermal. Most of it has a temperature in the range of 10-20 K, but there is also a significant fraction of warmer gas, located in low-extinction regions where photoelectric heating remains effective.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/11d2480c61914ea5a55b04c296117bb2ad87ac50

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Citations in the corpus

On the universality of interstellar filaments: theory meets simulations and observations (2015, background): “…(4) strictly speaking only applies to isothermal turbulence, while Smith et al. (2014) include a complex heating and cooling balance in their simulations, which only produces a nearly isothermal gas over a limited range of densities with a spatially varying sound speed (Glover et al. 2010).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Simulations of turbulent gas with molecule formation also suggest that I(CO) can be a very poor tracer of AV (Glover et al. 2010).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, methodology): “This is a reasonable approximation for dense, molecular gas of solar metallicity, over a wide range of densities (Wolfire et al. 1995; Omukai et al. 2005; Pavlovski et al. 2006; Glover & Mac Low 2007a,b; Glover et al. 2010; Hill et al. 2011; Hennemann et al. 2012).”
The SILCC (SImulating the LifeCycle of molecular Clouds) project - II. Dynamical evolution of the supernova-driven ISM and the launching of outflows (2015, methodology): “The thermal evolution of the gas is modelled using the detailed atomic and molecular cooling function described in Glover et al. (2010), Glover & Clark (2012) and Walch et al. (2015).”
A general model for the CO–H2 conversion factor in galaxies with applications to the star formation law (2011, methodology): “Glover et al. (2010) and Glover & Mac Low (2011) developed magnetohydrodynamic models of GMC evolution with timedependent chemistry to follow the formation and destruction of both H2 and CO.”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “Thus the CO abundance is generally always in equilibrium, though that equilibrium value may change as the H2 abundance does (Glover et al. 2010; Glover & Mac Low 2011; Glover & Clark 2012c).”
Phantom: A Smoothed Particle Hydrodynamics and Magnetohydrodynamics Code for Astrophysics (2017, methodology): “The cooling function in Phantom is based on a set of Fortran modules written by Glover & Mac Low (2007), updated further by Glover et al. (2010).”
Is molecular gas necessary for star formation (2011, background): “…chemistry (described in more detail below), as well as radiative heating and cooling from a number of atomic and molecular species (Glover & Jappsen 2007; Glover et al. 2010; Glover & Clark 2011), and an approximate treatment of the attenuation of the Galactic interstellar radiation field (ISRF).”
The density variance–Mach number relation in supersonic turbulence – I. Isothermal, magnetized gas (2012, methodology): “These variances are related by (e.g. Federrath et al. 2008b; Price et al. 2011) σ 2s = ln [ 1 + σ 2ρ/ρ0 ] .”
CO-dark gas and molecular filaments in Milky Way-type galaxies (2014, background): “On the other hand, small-scale models have for some time been able to model both H2 and CO formation in the turbulent ISM (see e.g. Glover et al. 2010; Glover & Clark 2012a), but have not had the dynamical range necessary to model cloud formation self-consistently, or have started from highly…”
LOW CO LUMINOSITIES IN DWARF GALAXIES (2012, background): “Numerical simulations even suggest that the ratios may never be constant inside a cloud because chemical equilibrium is not reached during most or all of a cloud’s lifetime (Glover et al. 2010; Glover & Mac Low 2011; Shetty et al. 2011a,b; Feldmann & Gnedin 2011).”
THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS). I. A CLOUD-SCALE/MULTI-WAVELENGTH VIEW OF THE INTERSTELLAR MEDIUM IN A GRAND-DESIGN SPIRAL GALAXY (2013, unknown): “Recently, Glover et al. (2010) modeled the CO formation.”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, background): “…an isothermal equation of state, which is a reasonable approximation for dense, molecular gas of solar metallicity, over a wide range of densities (Wolfire et al. 1995; Omukai et al. 2005; Pavlovski et al. 2006; Glover & Mac Low 2007a,b; Glover et al. 2010; Hill et al. 2011; Hennemann et al. 2012).”
The CO-H2 Conversion Factor in Disc Galaxies and Mergers (2011, methodology): “Building on the seminal work of Maloney & Black (1988) and more recent simulations of Glover et al. (2010); Glover & MacLow (2011) and Shetty et al. (2011a,b), we present the first models investigating the CO-H2 conversion factor in hydrodynamic simulations of isolated disc galaxies and disc galaxy…”
On the relationship between molecular hydrogen and carbon monoxide abundances in molecular clouds (2010, background): “In a previous paper (Glover et al. 2010, hereafter Paper I), we presented the first results from a project that aims to combine detailed chemical modelling with three-dimensional magnetohydrodynamical turbulence simulations in order to self-consistently model both the chemistry and the turbulent…”
Dusty Star Forming Galaxies at High Redshift (2014, methodology): “In the regime of large gas surface density,which ismore pertinent to the galaxies at hand, Feldmann et al. (2012a) coupled the GMC models of Glover et al. (2010) to a cosmological zoom simulation of an individual galaxy at z ∼ 2.”
The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae (2016, background): “The rate equations for H2 and CO include the effect of dust shielding and molecular (self-) shielding (Glover et al. 2010).”
Why are most molecular clouds not gravitationally bound (2011, methodology): “…et al. (2009) suggest that the masses of their clouds are underestimated by a factor of 2 due to non-LTE effects and CO abundance variations (see also calculations by Glover et al. (2010) and Shetty et al. (2010)) within a cloud, so we have doubled their cloud masses to produce the panel in Fig.”