ENVIRONMENTAL DEPENDENCE OF THE KENNICUTT–SCHMIDT RELATION IN GALAXIES

By Nickolay Y. Gnedin, Andrey V. Kravtsov. 2010

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We present a detailed description of a phenomenological H2 formation model and local star formation prescription based on the density of molecular (rather than total) gas. Such an approach allows us to avoid the arbitrary density and temperature thresholds typically used in star formation recipes in galaxy formation simulations. We present results of the model based on realistic cosmological simulations of high-z galaxy formation for a grid of numerical models with varied dust-to-gas ratios and interstellar far-UV (FUV) fluxes. Our results show that both the atomic-to-molecular transition on small, tens-of-parsec scales and the Kennicutt–Schmidt (K-S) relation on large, kiloparsec scales are sensitive to the dust-to-gas ratio and the FUV flux. The atomic-to-molecular transition as a function of gas density or column density has a large scatter but is rather sharp and shifts to higher densities with decreasing dust-to-gas ratio and/or increasing FUV flux. Consequently, star formation is concentrated to higher gas surface density regions, resulting in steeper slope and lower amplitude of the K-S relation at a given ΣH, in less dusty and/or higher FUV flux environments. We parameterize the dependences observed in our simulations in convenient fitting formulae, which can be used to model the dependence of the K-S relation on the dust-to-gas ratio and FUV flux in semi-analytic models and in cosmological simulations that do not include radiative transfer and H2 formation. Finally, we show that ionized gas can contribute a significant fraction of the total gas surface density in environments typical for high-redshift galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1c3af780f45588f6678a55f463e845716ec8394d

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Citations in the corpus

The relation between metallicity, stellar mass and star formation in galaxies: an analysis of observational and model data (2011, background): “One possible solution to the problem is that accreted gas is ‘hungup’ in the atomic phase of the ISM for some time, before it is able to reach high enough densities to form the molecular clouds in which stars are formed (Gnedin, Tassis & Kravtsov 2009; Gnedin & Kravtsov 2011).”
Implementing molecular hydrogen in hydrodynamic simulations of galaxy formation (2012, background): “…cosmological simulations of galaxies to determine deviations from the K-S relation in low metallicity galaxies (Gnedin & Kravtsov 2010) and with different dust-to-gas ratios and far-UV fluxes (Gnedin & Kravtsov 2011) and to study sources of scatter in the K-S relation (Feldmann et al. 2011).”
TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, methodology): “Gnedin & Kravtsov (2011) demonstrated that the density at which molecular fraction reaches 50% can be approximated as n∗ ≈ 25(Z/Z )−1 cm−3, (22) which we adopt in all of our simulations as the threshold for star formation.”
Evolution of the atomic and molecular gas content of galaxies (2013, methodology): “…empirical relation between molecular fraction and gas midplane-pressure from Blitz & Rosolowsky (2006), and one based on numerical hydrodynamic simulations in which the molecular fraction is highly dependent on the cold gas metallicity as well as the local UV background (Gnedin & Kravtsov 2011).”
Star formation in semi-analytic galaxy formation models with multiphase gas (2015, methodology): “We implement the GK recipe as it is given in Gnedin & Kravtsov (2011), with no tunable parameters.”
The neutral hydrogen content of galaxies in cosmological hydrodynamic simulations (2013, background): “Indeed, several groups have developed theoretical models to investigate this transition, and particularly its dependence on metallicity (Krumholz, McKee, & Tumlinson 2008; Gnedin & Kravtsov 2011).”
The dust content of galaxies from z = 0 to z = 9 (2016, methodology): “To compute the H2 fraction of the cold gas we use an approach based on the work by Gnedin & Kravtsov (2011).”
ON THE INTERPLAY BETWEEN STAR FORMATION AND FEEDBACK IN GALAXY FORMATION SIMULATIONS (2014, background): “Recent work by Gnedin et al. (2009, see also Gnedin & Kravtsov 2010, 2011; Kuhlen et al. 2012; Christensen et al. 2014) demonstrated how a star formation model based on the local abundance of H2 could explain the observed steepening for Σgas < 100M pc−2 in the Kennicutt-Schmidt (KS) relation for z…”
xCOLD GASS: The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies (2017, methodology): “For the EAGLE simulation, Lagos et al. (2015) implement the recipes of Gnedin & Kravtsov (2011) and Krumholz (2013); both have a dependence on the radiation field and the amount of metals in the ISM, but the latter has an additional dependence on the atomic gas column density.”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, methodology): “Various recipes for H2-formation, either employing the metallicity-based fitting functions of Krumholz et al. (2009) and Gnedin & Kravtsov (2011), or alternatively the empirical pressure-based recipe from Blitz & Rosolowsky (2004), have been implemented in these SAMs.”
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.”
Dark matter cores all the way down (2015, background): “…and difficult to model, due to uncertainties in dissociating UV radiation; self-shielding and shielding of H2 by dust (Krumholz et al. 2009; Gnedin et al. 2009; Gnedin & Kravtsov 2011); uncertain dust-to-gas ratios (Fisher et al. 2014); and the physics of line overlap (Gnedin & Draine 2014).”
Is molecular gas necessary for star formation (2011, background): “Although H2 can be an important coolant of interstellar gas (Gnedin & Kravtsov 2011), it is effective only at temperatures of a few hundred Kelvin or higher.”
Molecular hydrogen abundances of galaxies in the EAGLE simulations (2015, methodology): “For example, the physical drivers of the relation between the surface density of SFR and H2 have been explored in Feldmann, Gnedin & Kravtsov (2011), Gnedin & Kravtsov (2011, hereafter GK11), and Glover & Clark (2012).”