Star Formation at Very Low Metallicity. I. Chemistry and Cooling at Low Densities

By S. Glover, A. Jappsen. 2007

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We present a simplified chemical and thermal model designed to allow computationally efficient study of the thermal evolution of metal-poor gas within large numerical simulations. Our main simplification is the neglect of the molecular chemistry of the heavy elements. The only molecular chemistry retained within the model is the formation and destruction of molecular hydrogen. Despite this major simplification, the model allows for accurate treatment of the thermal evolution of the gas within a large volume of parameter space. It is valid for temperatures 50 < T < 10,000 K and metallicities 0 < Z < 0.1 Z☉. In gas with a metallicity Z = 0.1 Z☉, and in the absence of an incident ultraviolet radiation field, it is valid for hydrogen number densities nH ≲ 500/tchar cm-3, where tchar is the size in megayears of the characteristic physical timescale of interest in the problem. If Z ≪ 0.1 Z☉, or if a strong ultraviolet radiation field is present, then the model remains accurate up to significantly higher densities. We also discuss some possible applications of this model.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/01b696d46ecad8ab6c5088c1db684043fd9f1333

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Citations in the corpus

The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical–dynamical model of the thermosphere (2012, methodology): “We included651 this cooling mechanism in the C4 model by using the rate coefficient from652 Glover and Jappsen (2007) that includes a temperature-dependent correction653 to the rate coefficient given by Black (1981).”
Formation and evolution of primordial protostellar systems (2012, background): “The evolved species consist of H, H+, H−, H+2 , H2, He, He +, He++, D, D+, HD and free electrons (Glover & Jappsen 2007; Clark et al. 2011a).”
Hyper-Eddington accretion flows on to massive black holes (2015, background): “For the outer-region simulation, we assume optically thin cooling rates of H atoms (Lyα, ΛH = Λ thin Lyα), He atoms (1 1S state) and He+ ions, and freefree transitions (Glover & Jappsen 2007).”
Physical Processes in the Interstellar Medium (2014, methodology): “Compilations of excitation rate data are given in Hollenbach & McKee (1989), Glover & Jappsen (2007) and Maio et al. (2007), as well as in the LAMDA database (Schöier et al., 2005).”
Modelling CO formation in the turbulent interstellar medium (2009, methodology): “To do this, we largely follow the same prescription as in Glover & Jappsen (2007).”
Molecular hydrogen abundances of galaxies in the EAGLE simulations (2015, background): “However, we note that in parallel to our simple approach, the development of detailed chemistry networks and their application to individual galaxies is under way (e.g. Glover & Jappsen 2007; Richings, Schaye & Oppenheimer 2014a,b).”
LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “This gas has primordial composition, i.e. basically consists of hydrogen and helium, and cools mostly via H2 line emission (e.g. Anninos et al. 1997; Glover 2005; Glover & Jappsen 2007).”
MODELING MOLECULAR HYDROGEN AND STAR FORMATION IN COSMOLOGICAL SIMULATIONS (2008, background): “The latter reactions are comprehensively summarized elsewhere (Shapiro & Kang 1987; Abel et al. 1997; Galli & Palla 1998; Glover & Jappsen 2007; Glover & Abel 2008) and are not important for our purposes; we keep them in the equations to ensure that our model also works in the metal-free regime.”
Is molecular gas necessary for star formation (2011, background): “…of gas-phase 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…”
Resolving the Formation of Protogalaxies. III. Feedback from the First Stars (2007, methodology): “For gas with temperatures below 104 K, we calculate the additional cooling from carbon, oxygen, and silicon using the rates and reactions from Glover & Jappsen (2007).”
Uncertainties in H2 and HD chemistry and cooling and their role in early structure formation (2008, background): “Further details of our treatment of these processes can be found in Glover & Jappsen (2007).”