Molecular Hydrogen Regulated Star Formation in Cosmological Smoothed Particle Hydrodynamics Simulations

Abstract

Some observations have shown that star formation (SF) correlates tightly with the presence of molecular hydrogen (H 2 ); therefore, it is important to investigate its implication on galaxy formation in a cosmological context. In the present work, we implement a sub-grid model (hereafter H 2 -SF model) that tracks the H 2 mass fraction within our cosmological smoothed particle hydrodynamics code GADGET-3 by using an equilibrium analytic model of Krumholz et al. This model allows us to regulate the SF in our simulation by the local abundance of H 2 rather than the total cold gas density, which naturally introduces the dependence of SF on metallicity. We investigate the implications of the H 2 -SF model on galaxy population properties, such as the stellar-to-halo mass ratio (SHMR), baryon fraction, cosmic star formation rate density (SFRD), galaxy specific SFR, galaxy stellar mass functions (GSMF), and Kennicutt-Schmidt (KS) relationship. The advantage of our work over the previous ones is having a large sample of simulated galaxies in a cosmological volume from high redshift to z = 0. We find that low-mass halos with M DM < 10 10.5 M are less efficient in producing stars in the H 2 -SF model at z 6, which brings the simulations into better agreement with the observational estimates of the SHMR and GSMF at the low-mass end. This is particularly evident by a reduction in the number of low-mass galaxies at M 10 8 M in the GSMF. The overall SFRD is also reduced at high z in the H 2 run, which results in slightly higher SFRD at low redshift due to more abundant gas available for SF at later times. This new H 2 model is able to reproduce the empirical KS relationship at z = 0 naturally, without the need for setting its normalization by hand, and overall it seems to have more advantages than the previous pressure-based SF model.

The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties

“…Star formation in the simulations is governed by the SFR-versus-H 2 model of Krumholz et al (2009) rather than in terms of the total density in cold gas. The implementation of this in the GADGET-3 code is as described in Thompson et al (2014) and is similar to the implementation of the same recipe by Kuhlen et al (2013) in the Enzo code. As a result of the lower gas density in molecular hydrogen H 2 in fainter, lower-mass galaxies, the LFs predicted by Jaacks et al (2013) show a turn-over at approximately −15.4±0.6 mag.…”

GOLDRUSH. II. Clustering of galaxies at z ∼ 4–6 revealed with the half-million dropouts over the 100 deg2 area corresponding to 1 Gpc3

“…The solid curves show relations of Equation (23) Behroozi et al 2013b). The dashed, dotted, dot-dashed, and solid lines denote the predictions from theoretical studies of Thompson et al (2014), Okamoto et al (2014), Somerville et al (2015), and Illustris, respectively. The red and blue dashed lines correspond to the Fiducial and H 2 models in Thompson et al (2014).…”

SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [C ii]–SFR RELATIONSHIP OF MASSIVEz= 2 MAIN SEQUENCE GALAXIES

“…This model allows us to regulate star formation by the local abundance of H 2 rather than the total gas density, which confines star formation to the densest peaks of the ISM. Further implementation details can be found in Thompson et al (2014). Galactic outflows are implemented using the hybrid energy/ momentum-driven wind (ezw) model fully described in Davé et al (2013), Ford et al (2015.…”