MODELING MOLECULAR HYDROGEN AND STAR FORMATION IN COSMOLOGICAL SIMULATIONS

By Nickolay Y. Gnedin, K. Tassis, Andrey V. Kravtsov. 2008

203 citations recorded by the source corpus.

We describe a phenomenological model for molecular hydrogen formation suited for applications in galaxy formation simulations, which includes nonequilibrium formation of H2 on dust and approximate treatment of both its self-shielding and shielding by dust from the dissociating UV radiation. The model is applicable in simulations in which individual star-forming regions—the giant molecular complexes—can be identified (resolution of tens of parsecs) and their mean internal density estimated reliably, even if internal structure is not resolved. In agreement with previous studies, calculations based on our model show that the transition from atomic to fully molecular phase depends primarily on the metallicity, which we assume is directly related to the dust abundance, and clumpiness of the interstellar medium. The clumpiness simply boosts the formation rate of molecular hydrogen, while dust serves both as a catalyst of H2 formation and as an additional shielding from dissociating UV radiation. The upshot is that it is difficult to form fully shielded giant molecular clouds while gas metallicity is low. However, once the gas is enriched to Z ∼ 0.01–0.1 Z☉, the subsequent star formation and enrichment can proceed at a much faster rate. This may keep star formation efficiency in the low-mass, low-metallicity progenitors of galaxies very low for a certain period of time with the effect similar to a strong “feedback” mechanism. The effect may help explain the steep increase of the mass-to-light ratio toward smaller masses observed in the local galaxy population. We apply the model and star formation recipes based on the local amount of molecular gas to an output from a cosmological simulation of galaxy formation and show that resulting global correlations between star formation and gas, and H2 surface densities are in good agreement with observations.

Subfields: Astronomy and Astrophysics, Instrumentation, Organic Chemistry

View Paper: https://www.semanticscholar.org/paper/29d42054ff9505e95d19891f26f95a2aae71b0bc

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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.”
Cold gas properties of the Herschel Reference Survey - II. Molecular and total gas scaling relations (2014, background): “The simulations of Gnedin et al. (2009) indicate that e molecular phase depends primarily on metallicity, as is indeed observed in the HRS galaxies.”
The CO-H2 Conversion Factor in Disc Galaxies and Mergers (2011, background): “2006; Dobbs et al. 2008; Robertson & Kravtsov 2008; Pelupessy & Papadopoulos 2009; Gnedin et al. 2009; Gnedin & Kravtsov 2010).”
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).”
Implementing molecular hydrogen in hydrodynamic simulations of galaxy formation (2012, methodology): “In the only fully self-consistent implementation so far, Gnedin et al. (2009) implemented a model for the local nonequilibrium H2 abundances in their Adaptive Mesh Refinement (AMR) simulations.”
Photodissociation of H2 in protogalaxies: modelling self‐shielding in three‐dimensional simulations (2011, methodology): “…Wise & Abel 2007, 2008a,b; Greif et al. 2010), relied upon estimating NH2 from local properties of the gas (Bromm & Loeb 2003; Johnson et al. 2008; Gnedin et al. 2009; Shang et al. 2010; Johnson et al. 2011), or sacrificed angular resolution, finding the exact column density in a small number of…”
KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY (2012, background): “Possibilities included the inefficient formation of molecular hydrogen in metal-poor galaxies (e.g., Robertson&Kravtsov 2008; Gnedin et al. 2009; Krumholz & Dekel 2012), or an increase in the mass outflow rate per unit star formation with redshift.”
Physical Processes in the Interstellar Medium (2014, methodology): “…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 & Mac Low, 2007a; Dobbs et al., 2008; Gnedin et al., 2009; Christensen et al., 2012).”
FORMING REALISTIC LATE-TYPE SPIRALS IN A ΛCDM UNIVERSE: THE ERIS SIMULATION (2011, background): “The density threshold should depend on metallicity and therefore on redshift (Gnedin et al. 2009), which may affect the structure of the ISM and SN feedback differently in progenitors at different epochs.”
Numerical simulations of the dark universe: State of the art and the next decade (2012, background): “• Suppressing star formation in low mass and low metallicity systems by using H2-regulated star formation prescriptions rather than (or in conjunction with) SN feedback [336, 347];”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, methodology): “Some zoom simulations now include a simplified phenomenological treatment of chemical networks and H2 dust- and self-shielding (Christensen et al. 2012, Gnedin et al. 2009).”
REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED ΛCDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES (2012, background): “…and SN Feedback In a significant improvement, this new set of simulations include metal line cooling (Shen et al. 2010) and a dust dependent description of H2 creation and destruction by Lyman-Werner radiation and shielding of HI and H2 (Gnedin et al. 2009; Christensen et al. 2012, hereafter CH12).”
CO-dark gas and molecular filaments in Milky Way-type galaxies (2014, methodology): “Gnedin et al. (2009) presented a galactic scale model of molecular hydrogen formation in which these observations were used to calibrate a clumping factor, used to account for small-scale, unresolved density fluctuations, and tuned to ensure that the model matched observations.”
Galaxy formation theory (2010, background): “Numerous hydrodynamical simulation codes now contain implementations of chemical enrichment (Scannapiecoet al. 2005; Kobayashi et al. 2007; Pontzen et al. 2008; Gnedin et al. 2009).”
A COMPARISON OF METHODS FOR DETERMINING THE MOLECULAR CONTENT OF MODEL GALAXIES (2010, background): “…et al. 2009; Fu et al. 2010; Dutton et al. 2010), and simulations (Pelupessy et al. 2006; Robertson & Kravtsov 2008; Pelupessy & Papadopoulos 2009; Gnedin et al. 2009; Gnedin & Kravtsov 2010a,b) have all begun to incorporate models for the H i to H2 transition into their recipes for star…”
LOW CO LUMINOSITIES IN DWARF GALAXIES (2012, background): “This is pointed out by Gnedin et al. (2009), Gnedin & Kravtsov (2011), and Feldmann et al. (2011); they show that the gas densities containing H2 vary strongly with metallicity and radiation field, and thus free-fall times of clouds containing H2 are not constant.”