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Register a new userInfrared Emission from High-Redshift Galaxies in Cosmological SPH Simulations
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We compute the infrared (IR) emission from high-redshift galaxies in cosmological smoothed particle hydrodynamics simulations by coupling the output of the simulation with the population synthesis code `GRASIL by Silva et al. Based on the stellar mass, metallicity and formation time of each star particle, we estimate the full spectral energy distribution of each star particle from ultraviolet to IR, and compute the luminosity function of simulated galaxies in the Spitzer broadband filters for direct comparison with the available Spitzer observations.
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We investigate the structure of galaxies formed in a suite of high-resolution cosmological simulations. Consistent with observations of high-redshift galaxies, our simulated galaxies show irregular, prolate shapes with thick stellar disks, which are dominated by turbulent motions instead of rotation. Yet molecular gas and young stars are restricted to relatively thin disks. We examine the accuracy of applying the Toomre linear stability analysis to predict the location and amount of gas available for star formation. We find that the Toomre criterion still works for these irregular galaxies, after correcting for multiple gas and stellar components: the $Q$ parameter in $rm{H_2}$ rich regions is in the range $0.5-1$, remarkably close to unity. Due to the violent stellar feedback from supernovae and strong turbulent motions, young stars and molecular gas are not always spatially associated. Neither the $Q$ map nor the $rm{H_2}$ surface density map coincide with recent star formation exactly. We argue that the Toomre criterion is a better indicator of future star formation than a single $rm{H_2}$ surface density threshold because of the smaller dynamic range of $Q$. The depletion time of molecular gas is below 1~Gyr on kpc scale, but with large scatter. Centering the aperture on density peaks of gas/young stars systematically biases the depletion time to larger/smaller values and increases the scatter.
We present the McMaster Unbiased Galaxy Simulations (MUGS), the first 9 galaxies of an unbiased selection ranging in total mass from 5$times10^{11}$ M$_odot$ to 2$times10^{12}$ M$_odot$ simulated using n-body smoothed particle hydrodynamics (SPH) at high resolution. The simulations include a treatment of low temperature metal cooling, UV background radiation, star formation, and physically motivated stellar feedback. Mock images of the simulations show that the simulations lie within the observed range of relations such as that between color and magnitude and that between brightness and circular velocity (Tully-Fisher). The greatest discrepancy between the simulated galaxies and observed galaxies is the high concentration of material at the center of the galaxies as represented by the centrally peaked rotation curves and the high bulge-to-total ratios of the simulations determined both kinematically and photometrically. This central concentration represents the excess of low angular momentum material that long has plagued morphological studies of simulated galaxies and suggests that higher resolutions and a more accurate description of feedback will be required to simulate more realistic galaxies. Even with the excess central mass concentrations, the simulations suggest the important role merger history and halo spin play in the formation of disks.
We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we combine, implement, modify and test a vast majority of SPH improvement techniques in the latest instalment of the GADGET code. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity, which includes a high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and largely improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic disks to be colder, thinner and more extended and our results on galaxy clusters show entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard SPH, thus becoming the core of an efficient code for large cosmological simulations.
In order to investigate the structure and dynamics of the recently discovered massive (M_* > 10^11 M_sun) compact z~2 galaxies, cosmological hydrodynamical/N-body simulations of a proto-cluster region have been undertaken. At z=2, the highest resolution simulation contains ~5800 resolved galaxies, of which 509, 27 and 5 have M_* > 10^10 M_sun, > 10^11 M_sun and > 4x10^11 M_sun, respectively. Effective radii and characteristic stellar densities have been determined for all galaxies. At z=2, for the definitely well resolved mass range of M_* > 10^11 Msun, the mass-size relation is consistent with observational findings for the most compact z~2 galaxies. The very high velocity dispersion recently measured for a compact z~2 galaxy (~510 km/s; van Dokkum et al 2009) can be matched at about the 1-sigma level, although a somewhat larger mass than the estimated M_* ~ 2 x 10^11 M_sun is indicated. For the above mass range, the galaxies have an average axial ratio <b/a> = 0.64 +/- 0.02 with a dispersion of 0.1, an average rotation to 1D velocity dispersion ratio <v/sigma> = 0.46 +/- 0.06 with a dispersion of 0.3, and a maximum value of v/sigma ~ 1.1. Rotation and velocity anisotropy both contribute in flattening the compact galaxies. Some of the observed compact galaxies appear flatter than any of the simulated galaxies. Finally, it is found that the massive compact galaxies are strongly baryon dominated in their inner parts, with typical dark matter mass fractions of order only 20% inside of r=2R_eff.
I highlight three results from cosmological hydrodynamic simulations that yield a realistic red sequence of galaxies: 1) Major galaxy mergers are not responsible for shutting off star-formation and forming the red sequence. Starvation in hot halos is. 2) Massive galaxies grow substantially (about a factor of 2 in mass) after being quenched, primarily via minor (1:5) mergers. 3) Hot halo quenching naturally explains why galaxies are red when they either (a) are massive or (b) live in dense environments.
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