Implementing Feedback in Simulations of Galaxy Formation: A Survey of Methods

By R. Thacker, Hugh M. P. Couchman. 2000

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We present a detailed description, and examine the performance of, a number of different approaches to modeling feedback in simulations of galaxy formation. Gasdynamic forces are evaluated using smoothed particle hydrodynamics (SPH). Star formation and supernova feedback are included using a three-parameter model which determines the star formation rate (SFR) normalization, feedback energy, and lifetime of feedback regions. The star formation rate is calculated for all gas particles which fall within prescribed temperature, density, and convergent flow criteria, and for cosmological simulations we also include a self-gravity criterion for gas particles to prevent star formation at high redshifts. A Lagrangian Schmidt law is used to calculate the star formation rate from the SPH density. Conversion of gas to stars is performed when the star mass for a gas particle exceeds a certain limit, typically half that of the gas particle. Feedback is incorporated by returning a precalculated amount of energy to the ISM as thermal heating. We compare the effects of distributing this energy over the smoothing scale or depositing it on a single particle. Radiative losses are prevented from heated particles by adjusting the density used in radiative cooling so that the decay of energy occurs over a set half-life, or by turning off cooling completely and allowing feedback regions a brief period of adiabatic expansion. We test the models on the formation of galaxies from cosmological initial conditions and also on isolated disk galaxies. For isolated prototypes of the Milky Way and the dwarf galaxy NGC 6503 we find feedback has a significant effect, with some algorithms being capable of unbinding gas from the dark matter halo ("blow-away"). As expected feedback has a stronger effect on the dwarf galaxy, producing significant disk evaporation and also larger feedback "bubbles" for the same parameters. In the critical-density CDM cosmological simulations, evolved to a redshift z = 1, we find that, barring extreme models, feedback has little effect. Further, feedback only manages to produce a disk with a specific angular momentum value approximately twice that of the run with no feedback, the disk thus has an specific angular momentum value that is characteristic of observed elliptical galaxies. We argue that this is a result of the extreme central concentration of the dark halos in the standard CDM model and the pervasiveness of the core-halo angular momentum transport mechanism (even in light of feedback). A simulation with extremely violent feedback, relative to our fiducial models, leads to a disk that resembles the other simulations at z = 1 and has a specific angular momentum value that is more typical of observed disk galaxies. At later times, z = 0.5, a large amount of halo gas which does not suffer an angular momentum deficit is present; however, the cooling time is too long to accrete on to the disk. We further point out that the disks formed in hierarchical simulations are partially a numerical artifact produced by the minimum mass scale of the simulation acting as a highly efficient "support" mechanism. Disk formation is strongly affected by the treatment of dense regions in the SPH method. The problems inherent in the treatment of high-density regions in SPH, in concert with the difficulty of representing the hierarchical formation process, means that realistic simulations of galaxy formation require far higher particle resolution than currently used.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c8fe263dfd7399376673acb3a738cc138ec23d4a

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Citations in the corpus

The history of star formation in a lcdm universe (2002, background): “…Yepes et al., 1997; Weinberg et al., 1997, 2002; Steinmetz & Müller, 1995; Blanton et al., 1999; Pearce et al., 1999, 2001; Thacker et al., 2000; Thacker & Couchman, 2000), progress has been comparatively slow with this approach, primarily because of the physical complexity of star formation…”
Feedback in simulations of disc-galaxy major mergers (2005, background): “In addition, several authors investigated a range of values for c⋆ (Bekki & Shioya 1998; Thacker & Couchman 2000) as we do in §5.2, or use a hybrid model where c⋆ can change with redshift or environment (Sommer-Larsen et al. 2003; Okamoto et al. 2005).”
Damped Lyman α systems in galaxy formation simulations (2008, background): “This has the well-known effect of causing the supernovae energy to be radiated away over much less than the dynamical timescale (Katz 1992; Thacker & Couchman 2000) and is thus the weakest conceivable mechanism.”
REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED ΛCDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES (2012, methodology): “Incremental improvements based on more realistic SN feedback (Thacker & Couchman 2000; Stinson et al. 2006) led to simulations that formed galaxies with extended disks (Governato et al. 2009; Brooks et al. 2011), but still substantially overproduced stars.”
The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, background): “…disc overcooling, clumping, fragmentation and angular momentum transport (Weil, Eke & Efstathiou 1998; Sommer-Larsen, Gelato & Vedel 1999; Thacker & Couchman 2000, 2001; Abadi et al. 2003; Sommer-Larsen, Götz & Portinari 2003; Governato et al. 2004, 2007; Robertson et al. 2004; Okamoto…”
A primer on hierarchical galaxy formation: the semi-analytical approach (2006, background): “Kay et al. (2002) present a useful review of the various prescriptions used in gas dynamical simulations to turn cold gas into stars (see also Thacker & Couchman 2000).”
On the relation between the Schmidt and Kennicutt-Schmidt star formation laws and its implications for numerical simulations (2007, background): “…& Mueller 1994; Mihos & Hernquist 1994; Katz, Weinberg, & Hernquist 1996; Gnedin 1996; Gerritsen & Icke 1997; Yepes et al. 1997; Springel 2000; Thacker & Couchman 2000; Kay et al. 2002; Kawata & Gibson 2003; Kravtsov 2003; Springel & Hernquist 2003; Sommer-Larsen, Götz, & Portinari 2003;…”
The structure of the interstellar medium of star‐forming galaxies (2011, background): “Thus far, however, many calculations that model stellar feedback explicitly have invoked only thermal heating via SNe (e.g. Thacker & Couchman 2000; Governato et al. 2007; Ceverino & Klypin 2009; Teyssier, Chapon & Bournaud 2010).”
Numerical simulations of the dark universe: State of the art and the next decade (2012, methodology): “At the limited resolution of current simulations, feedback is implemented using heuristic and often ad-hoc prescriptions (for a review, see [359]).”
Galaxy formation theory (2010, methodology): “…and so the treatment of the physics is often at the “subgrid” level, which essentially means that it is put in by hand using a semianalytic approach (Thacker and Couchman 2000; Kay et al. 2002; Marri and White 2003; White 2004; Stinson et al. 2006; Cox et al. 2006; Scannapieco et al. 2006a;…”
The effect of galaxy mass ratio on merger-driven starbursts (2007, background): “Unfortunately, there are often a range of acceptable free parameters which produce distinct star formation histories or remnant morphologies (see, e.g., Thacker & Couchman 2000; Kay et al. 2002; Springel et al. 2005b; Cox et al. 2006).”
Molecular Hydrogen and Global Star Formation Relations in Galaxies (2007, background): “…structure of the ISM that may develop through feedback from star formation (e.g., Yepes et al. 1997; Hultman & Pharasyn 1999; Springel 2000; Thacker & Couchman 2000; Springel & Hernquist 2003a; Stinson et al. 2006; Schaye & Dalla Vecchia 2008) may also serve to ameliorate numerical Jeans…”
Feedback and the fundamental line of low-luminosity low-surface-brightness/dwarf galaxies (2002, background): “…be transferred to the gas in either bulk kinetic energy or thermal energy, but it can also be kept in reservoirs of other forms such as turbulence, which would amplify the feedback effects on the gas (e.g. Efstathiou 2000; Springel 2000; Thacker & Couchman 2000, 2001; Springel & Hernquist 2003a,b).”
A model for cosmological simulations of galaxy formation physics: multi-epoch validation (2013, background): “…2008; Okamoto et al. 2010; Hopkins et al. 2012c) or suppression of radiative cooling after injection of thermal energy (e.g., Gerritsen & Icke 1997; Thacker & Couchman 2000; Kawata & Gibson 2003; Sommer-Larsen et al. 2003; Brook et al. 2004; Stinson et al. 2006; Piontek & Steinmetz 2011; Dalla…”
Gusty, gaseous flows of FIRE: Galactic winds in cosmological simulations with explicit stellar feedback (2015, methodology): “The second approach uses the socalled ‘blastwave’ model to account for the unresolved expansion phase of the SN remnant following the explosion (e.g. Thacker & Couchman 2000; Stinson et al. 2006, 2013; Governato et al. 2007; Guedes et al. 2011; Shen et al. 2014; Christensen et al. 2015).”
A Merger-driven Scenario for Cosmological Disk Galaxy Formation (2005, background): “…these discrepancies in a cosmological context have mainly relied on increasing the impact of feedback from star formation (Weil et al. 1998; Sommer-Larsen et al. 1999, 2003; Thacker & Couchman 2000, 2001; Abadi et al. 2003a; Governato et al. 2004; Robertson et al. 2004; Okamoto et al. 2005).”
The Emergence of the Thick Disk in a Cold Dark Matter Universe (2004, methodology): “This is similar to a model presented in Thacker & Couchman (2000) The semi-cosmological version of GCD+ used here is based upon the galaxy formation model of Katz & Gunn (1991).”
The birth of a galaxy – II. The role of radiation pressure (2012, background): “One approach is to neglect radiative cooling within the blastwave, allowing it to adiabatically expand (e.g. Thacker & Couchman 2000; Governato et al. 2007; Guedes et al. 2011).”