Implementing molecular hydrogen in hydrodynamic simulations of galaxy formation

By C. Christensen, Thomas R. Quinn, Fabio Governato, Adrienne Stilp, S. Shen, James Wadsley. 2012

145 citations recorded by the source corpus.

Motivated by the observed connection between molecular hydrogen (H2) and star formation, we present a method for tracking the non-equilibrium abundance and cooling processes of H2 and H2-based star formation in smoothed particle hydrodynamic simulations. The local abundances of H2 are calculated by integrating over the hydrogen chemical network. This calculation includes the gas phase and dust grain formation of H2, shielding of H2 and photodissociation of H2 by Lyman–Werner radiation from nearby stellar populations. Because this model does not assume equilibrium abundances, it is particularly well suited for simulations that model low-metallicity environments, such as dwarf galaxies and the early Universe. We further introduce an explicit link between star formation and local H2 abundance. This link limits star formation to ‘star-forming regions’, represented by areas with abundant H2. We use simulations of isolated disc galaxies to verify that the transition from atomic to molecular hydrogen occurs at realistic densities and surface densities. Using these same isolated galaxies, we establish that gas particles of 104 M⊙ or less are necessary to follow the molecular gas in this implementation. With this implementation, we determine the effect of H2 on star formation in a cosmological simulation of a dwarf galaxy. This simulation is the first cosmological simulation with non-equilibrium H2 abundances to be integrated to a redshift of zero or to include efficient supernova feedback. We analyse the amount and distribution of star formation in the galaxy using simulated observations of the H i gas and in various optical bands. From these simulated observations, we find that our simulations are consistent with the observed Tully–Fisher, global Kennicutt–Schmidt and resolved Kennicutt–Schmidt relations. We find that the inclusion of shielding of both the atomic and molecular hydrogen and, to a lesser extent, the additional cooling from H2 at temperatures between 200 and 5000 K increases the amount of cold gas in the galaxies. The changes to the interstellar medium (ISM) result in an increased amount of cold, dense gas in the disc of the galaxy and the formation of a clumpier ISM. The explicit link between star formation and H2 and the clumpier ISM results in a bluer galaxy with a greater spatial distribution of star formation at a redshift of zero.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d4d123455ed36ced42bc341d17da52fd5774e4cd

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Citations in the corpus

Towards a more realistic population of bright spiral galaxies in cosmological simulations (2013, background): “Christensen et al. (2012) have shown that the implementation of a model for the formation of molecular hydrogen (see Gnedin et al. 2009) can amplify the effect of higher threshold densities.”
Theoretical Challenges in Galaxy Formation (2016, unknown): “…Kennicutt et al. 2007, Leroy et al. 2008, Wong & Blitz 2002) and use a constant time-scale in combination with the variable local H2 fraction (e.g. Christensen et al. 2012; Feldmann, Gnedin & Kravtsov 2012; Gnedin, Tassis & Kravtsov 2009; Kuhlen et al. 2012; Monaco et al. 2012; Pelupessy,…”
Star formation in semi-analytic galaxy formation models with multiphase gas (2015, methodology): “…in order to understand the complex physical processes involved, extremely high resolution is required in order to obtain reliable results (see e.g. Christensen et al. 2012), implying that it will be feasible to simulate only small numbers of galaxies with these techniques for the next few years.”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…or MHD simulation (Koyama & Inutsuka 2000; Bergin et al. 2004; Glover & Mac Low 2007a,b; Pelupessy & Papadopoulos 2009; Gnedin et al. 2009; Christensen et al. 2012; Mac Low & Glover 2012; Clark et al. 2012a; Inoue & Inutsuka 2012), which can be either one-dimensional or three-dimensional.”
Molecular hydrogen abundances of galaxies in the EAGLE simulations (2015, methodology): “…of the ISM and in individual galaxy simulations in which H2 formation has been implemented (e.g. Pelupessy, Papadopoulos & van der Werf 2006; Robertson & Kravtsov 2008; Gnedin, Tassis & Kravtsov 2009; Pelupessy & Papadopoulos 2009; Christensen et al. 2012; Glover & Clark 2012; Walch et al. 2015).”
Evolution of the atomic and molecular gas content of galaxies (2013, background): “…and cosmological numerical hydrodynamic simulations, tracking the multi-phase gas content and implementing H2-based star formation prescriptions (e.g. Pelupessy, Papadopoulos & van der Werf 2006; Robertson & Kravtsov 2008; Gnedin & Kravtsov 2011; Christensen et al. 2012; Kuhlen et al. 2012).”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, methodology): “…of molecular gas (Krumholz & Dekel 2012), but hydrodynamic simula- Models of Galaxy Formation 39 tions and SAMs incorporating H2 formation modeling suggest that this effect is not large enough to solve the problem at the observed mass scales (Christensen et al. 2012, Somerville et al. 2014).”
REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED ΛCDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES (2012, methodology): “…utilized is described in detail in Section 2 and has been analyzed in other papers showing that the galaxies follow the Kennicutt-Schmidt law (Christensen et al. 2012), have cored DM profiles similar to the observed ones (Oh et al. 2011; Governato et al. 2012) and realistic satellite…”
H$_2$ formation on interstellar dust grains: the viewpoints of theory, experiments, models and observations (2017, background): “Since molecular hydrogen also contributes to the cooling of the gas, it is perhaps expected that abundances of H2 should affect the star formation rate and the spatial distribution of star forming regions (Christensen et al., 2012).”
Physical Processes in the Interstellar Medium (2014, background): “In the case of H and H2, the simplicity of the chemistry makes this relatively straightforward, and a number of different implementations of H2 formation chemistry within large hydrodynamical simulations are now available (see e.g. Anninos et al. 1997; Glover and Mac Low 2007a; Dobbs et al. 2008; Gn”
The SILCC (SImulating the LifeCycle of molecular Clouds) project – I. Chemical evolution of the supernova-driven ISM (2014, background): “…(2015) chemistry of H2 within galactic-scale simulations of the ISM (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Dobbs, Burkert & Pringle 2011; Christensen et al. 2012), and more recently a couple of studies have also treated CO formation (Pettitt et al. 2014; Smith et al. 2014).”
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): “C O ] 2 2 Ju Kravtsov 2008; Gnedin et al. 2009; Christensen et al. 2012).”
CO-dark gas and molecular filaments in Milky Way-type galaxies (2014, background): “…performed large-scale dynamical simulations of the ISM that account for H2 formation (see e.g. Dobbs et al. 2008; Gnedin, Tassis & Kravtsov 2009; Christensen et al. 2012), but these models typically have insufficient resolution to allow one to study individual giant molecular clouds (GMCs) in…”
BARYONS MATTER: WHY LUMINOUS SATELLITE GALAXIES HAVE REDUCED CENTRAL MASSES (2012, background): “Self-shielding, combined with a low temperature cooling model, allows the already cool gas in the galaxy to cool even further, making the star formation even clumpier and the feedback therefore even more efficient (Christensen et al. 2012; Susa 2008, Christensen et al., in prep.).”