INVITED TALKS
Klaus Dolag - MPA Garching
Clusters of galaxies are ideal cosmological probes. They are the largest collapsed objects in the Universe and so are very sensitive to the structure formation process. Therefore cosmological simulations are of high interest for the scientific community and harbor enormous potential for the interpretation of observational data. Such simulations are extremely challenging, as the structures in and around clusters span a very large dynamic range in scales. Furthermore, the complexity of the intra cluster medium revealed by multi-frequency observations demonstrates that a variety of physical processes are in action and must be included to produce accurate and realistic models. I will show how this can be achieved in numerical simulations of the formation of galaxy clusters in cosmological context.
Joop Schaye - Leiden Observatory
Simulating the formation of galaxies and the evolution of the intergalactic medium
The OverWhelmingly Large Simulations (OWLS) project aims to study the formation of galaxies and the evolution of the intergalactic medium using a large suite of cosmological gas-dynamical simulations. The simulations are repeated many times using different physical and numerical parameters. This strategy enables us to carefully check for numerical artifacts and to pinpoint relevant physical processes. I will present a selection of preliminary results from the OWLS project.
Kentaro Nagamine - University of Nevada
Galaxy Formation Simulations: successes and failures
Cosmological hydrodynamic simulations have played various important roles in checking the validity of cold dark matter (CDM) model. In this talk, I will review the past efforts to reproduce the properties of low- & high-redshift galaxies, such as the luminosity/mass functions, colors and metallicity, as well as the properties of damped Ly-a systems. I will discuss the successes and failures of Lambda CDM simulations with a focus on the role of feedback and star formation.
Tom Theuns - ICC-Durham
The interaction between galaxies and the intergalactic medium
The physics of how gas accretes into dark mater potential wells and gets converted into stars is complex. Feedback from stars and AGN regulates a complex multi-phase interstellar medium, in which magnetic fields, cosmic rays, the chemistry of molecule and dust formation, the large-scale density field in the galaxy, etc all play a role. Understanding all these effects in detail, and modelling them correctly is a huge computational challenge. I describe an extensive set of simulations that use a variety of sub-grid models to investigate the extent to which predictions from simulations are sensitive to details of the model.
Romeel Dave - Steward Observatory
Simulations of Galaxy Formation Including Outflows
I highlight key results from our recent simulations incorporating a heuristic but well-constrained model for galactic outflows. I show that a single outflow model matches a wide range of observations of chemical enrichment, including IGM metal absorbers, the galaxy mass-metallicity relation, and ICM metallicities. I describe important new insights into the physical processes governing galaxy evolution obtained from these simulations.
Andrea Ferrara - SISSA
Feedback processes at Cosmic Dawn: Numerical Views
The formation of the first stars is thought to occur in very low mass sub-galactic units within the first Gyr of the cosmic history. These metal-free (or virtually so) stars might have masses of more than one hundred times the Sun, and therefore are expected to end their life as pair-instability/core collapse supernovae. The energy and heavy element deposition by supernovae will affect the star formation rate within the first galaxies and the initial mass function of their stars, via a series of physical processes collectively known as "feedback". Numerical simulations can now implement the relevant physics to follow in detail these early phases of cosmic evolution. The results from the most recent studies will be presented.
Stefano Borgani - Dept. of Astronomy, University of Trieste
Feedback effects on the chemo- and thermo-dynamics of the ICM
I will present results from cosmological hydrodynamical simulations of galaxy clusters aimed at studying the thermal structure of the intra-cluster medium and its history of chemical enrichment. I will focus the presentation on the effect that feedback from supernovae and AGN has on the observational properties of the hot diffuse cluster baryons. The simulation results will be compared with the observational data in the X-ray band. This comparison will concentrate on the profiles of entropy, temperature and metallicity, as well as on scaling relations between X-ray observables. I will finally discuss the impact of these different feedback sources on the optical/near-IR properties of the cluster galaxy population.
Matteo Viel - INAF & INFN, Trieste
The high redshift intergalactic medium as a cosmological probe
I will review the role of the Lyman-alpha forest as a tracer of intergalactic structures in the high redshift universe. I will describe the hydrodynamical simulations used to interpret the high and low resolution quasar data sets available and the main physical ingredients that have been incorporated in the numerical codes to properly simulate the transmitted Lyman-alpha flux. I will discuss the results in terms of: cosmological parameters and sinergies with other large scale structure observables; coldness of cold dark matter particles and their effect on the intergalactic medium; non-gaussianities at high redshift; the intergalactic medium thermal state and its evolution with redshift.
Lucio Mayer - University of Zurich
Galaxy formation simulations in a CDM Universe
I will discuss the progress made by numerical simulations of galaxy formation over the last ten years, focusing on the formation of disk galaxies. I will show how several long standing issues have been largely overcome thanks to a combination of increased numerical resolution and better models for star formation and the energy balance of the interestellar medium. This suggests that even the remaining open problems, such as the origin of bulgeless galaxies, will likely find their solution as we improve further our modeling of astrophysical processes in the simulations. Therefore it would appear that the formation of disks with large angular momentum as the observed ones is not necessarily at odds with the way structure forms in the cold dark matter model, contrary to previous belief. Galaxy formation is probably a better laboratory for testing our knowledge of astrophysics rather than cosmology. Among the interesting new astrophysical aspects of galaxy formation shown by simulations, I will describe the role of clumpy gas accretion via thermal instability and smooth accretion via a cooling flow in a hot corona around galaxies, discussing the connection with observed high velocity clouds (HVCs) and extraplanar gas in the neary galaxies. These phenomena will be major testing ground for the upcoming Square Kilometer Array (SKA).
Marcus Brueggen - Jacobs University Bremen
Simulation of the AGN-ICM interaction
I will review recent work on the interaction between active galactic nuclei (AGN) and the intracluster medium (ICM). Feedback by hot, underdense bubbles powered by AGN play a key role in structure formation. The simulation of this interaction is not trivial. While pure-hydro simulations indicate that AGN bubbles are disrupted into resolution-dependent pockets of underdense gas, proper modeling of subgrid turbulence indicates that this a poor approximation to a turbulent cascade that continues far beyond the resolution limit. Instead, Rayleigh-Taylor instabilities act to effectively mix the heated region with its surroundings, while at the same time preserving it as a coherent structure, consistent with observations. Properly capturing the evolution of such bubbles has important implications for many ICM properties. In particular, it significantly changes the impact of AGN-driven clouds on the mixing of metals into the ICM as well as in determining the entropy profiles in cool-core clusters such as the Perseus Cluster.
Benedetta Ciardi - MPA Garching
Simulations of reionization
With the advent in the near future of radio telescopes as LOFAR, a new window on the high- redshift universe will be opened. In particular, it will be possible, for the first time, to observe the 21cm signal from the diffuse Intergalactic Medium (IGM) prior to its reionization and thus probe the "dark ages". In this talk I will present results of simulations of IGM reionization and discuss its observability.
Greg Bryan - Columbia University
Simulating the Circumgalactic Medium
We use numerical simulations to probe the warm-hot gas halo that is predicted to surround normal disk galaxies, suggesting the term "Circumgalactic Medium" for such gas. We focus on gas accretion and outflows using high-resolution cosmological simulations. The output of these simulations is used to predict a variety of observational signatures including X-ray emission and UV absorption/emission lines, demonstrating that Lya, OVI, and CIV spectral lines (among others) will be important diagnostics of the strength of feedback in such galaxies.
Andreas Burkert - (LMU München)
The cosmological angular momentum problem and the formation of galactic disks
Within the cosmological cold dark matter scenario, galactic disks form when gas falls into dark matter halos, dissipates its kinetic and potential energy and settles into the equatorial plane.
The specific angular momentum distribution of the gas determines the size and surface density distribution of the resulting disk galaxies and therefore is of fundamental importance in order to understand how spiral galaxies form and evolve.
It is generally believed that the gas initially has a specific angular momentum distribution that is similar to the angular momentum distribution of the dark matter component, which can been determined with high precision through high-resolution cold dark matter simulations.
This predicted distribution is however not in agreement with the observed structure of galactic disks. First of all, galactic disks, forming in this way should have strongly centrally peaked surface density distributions that are not observed.
In addition, the gas during its infall looses a substantial amount of angular momentum by dynamical friction, leading to disk galaxies with scale lengths that are up to one order of magnitude smaller than observed.
In my talk I will discuss the various aspects of the cosmological angular momentum problem of galaxy formation and summarize possible solutions.
John Wise - NASA - Goddard
Starting reionization with the first stars
The first stars are thought to be extremely luminous and reside in dark matter halos with masses of approximately a million solar masses.
I will present results from radiation hydrodynamics simulations that follow the formation of tens of metal-free stars and their impact on high-redshift galaxy formation and reionization. HII regions created by the first stars are a few kiloparsecs in radius, which then overlap with each other and constitute a volume filling fraction of about a quarter at redshift 15. Our simulations also include pair-instability supernovae and the ensuing chemical enrichment of the IGM and subsequent star formation. We find that the first galaxies are enriched up to 1/1000th of solar metallicity, which is sufficient to transition to lower-mass star formation.
Andrey Kravtsov - Univ. of Chicago
Modeling molecular gas and star formation in high-resolution cosmological simulations
I will describe the newly developed algorithm for modeling formation of molecular hydrogen in cosmological simulations of galaxy formation. The algorithm accounts for H2 formation on dust and self-shielding processes and is tuned to correctly reproduced the trends with metallicity observed in the Milky Way and the Magellanic Clouds.
I will then discuss the model of star formation that is tied to molecular hydrogen density rather than to the total gas density (as is usually done in simulations) and discuss potential differences in the evolution of galaxies between these prescriptions.
Oleg Gnedin - University of Michigan
Modeling Star Formation in Dark Matter Halos
I will discuss analytical and numerical approaches to modeling star formation in galactic halos, with an emphasis on disk galaxies and dwarf galaxies. Important phenomenological constraints on the models can be obtained from matching the observed distributions of stellar masses and kinematics. I will also describe the current status of the "missing satellites problem" and the latest models that help explain detailed star formation histories of dwarf galaxies in the Local Group.
Renyue Cen - Princeton University
Simulations of Galaxy Formation and Cosmological Reionization
I will present some results from three types of cosmological simulations that we recently performed: 1) large-scale cosmological simulations of reionization with detailed 3-d radiative transfer and hydrodynamics, 2) ultra-high resolution radiative transfer hydrodynamic simulations of star formation and ionizing photon propagation, 3) large-scale cosmological galaxy formation simulations.