1. Dark Matter Halos in the Standard Cosmological Model: Results from the Bolshoi Simulation A. A. Klypin, S. Trujillo-Gomez, J. Primack, ApJ, 740, 102 (2011). [Desc][abs, pdf , ps, other] A pdf of this article is also available on the HiPACC Server: pdf
   Comments: 28 pages, 22 figures, published in The Astrophysical Journal (ApJ)
   
   
2. Galaxies in ΛCDM with Halo Abundance Matching: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, Velocity Function, and Clustering S. Trujillo-Gomez, A. A. Klypin, J. Primack, A. Romanowsky, ApJ, 742, 16 (2011). [Desc][abs, pdf, ps, other]
   A pdf of this article is also available on the HiPACC Server: pdf
   Comments: 40 pages, 18 figures, published in ApJ
   
   
3. The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds Michael T. Busha , Philip J. Marshall, Risa H. Wechsler, Anatoly Klypin, Joel Primack, ApJ, 743, 40 (2011). [Desc][abs, pdf, ps, other]
   A pdf of this article is also available on the HiPACC Server: pdf
   Comments: 9 pages, replaced with version published in ApJ. Animations available at this http URL
   
   
4. Statistics of Satellite Galaxies Around Milky Way-Like Host Michael T. Busha, Risa H.Wechsler, Peter S. Behroozi, Brian F. Gerke, Anatoly A. Klypin, Joel R. Primack, ApJ, 743, 117 (2011).[Desc][abs, pdf, ps, other]
   A pdf of this article is also available on the HiPACC Server: pdf
   Comments: 14 pages. Replaced with version accepted to ApJ. Some animations available at this http URL


5. Halo concentrations in the standard LCDM cosmology Francisco Prada, Anatoly A. Klypin, Antonio J. Cuesta, Juan E. Betancort-Rijo, Joel Primack [Desc][abs, pdf, ps, other]
   Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)
   
   
6. The MultiDark Database: Release of the Bolshoi and MultiDark Cosmological Simulations Kristin Riebe, Adrian M. Partl, Harry Enke, Jaime Forero-Romero, Stefan Gottloeber, Anatoly Klypin, Gerard Lemson, Francisco Prada, Joel R.
   Primack, Matthias Steinmetz, Victor Turchaninov [Desc][abs, pdf, other]
   Comments: 28 pages, 9 figures, submitted to New Astronomy
   
   
7. The Rockstar Phase-Space Temporal Halo Finder and the Velocity Offsets of Cluster Cores Peter S. Behroozi, Risa H. Wechsler, Hao-Yi Wu [Desc]
   Comments: 20 pages, 14 figures. Submitted to ApJ; revised to correct URL in abstract and include additional references


8. Gravitationally Consistent Halo Catalogs and Merger Trees for Precision Cosmology
   Peter S. Behroozi, Risa H. Wechsler, Hao-Yi Wu, Michael T. Busha, Anatoly Klypin, Joel Primack. [Desc]
   [abs, pdf, other]
   Comments: 15 pages, 12 figures. Submitted to ApJ; URL in abstract corrected

Descriptions

1. The Astrophysical Journal > Volume 740 > Number 2
   Dark Matter Halos in the Standard Cosmological Model: Results from the Bolshoi Simulation
   A. Klypin, S. Trujillo-Gomez, J. Primack
   [abs, pdf , ps, other]
   
   (Submitted on 19 Feb 2010 (v1), last revised 16 Aug 2011 (this version, v4))
   Lambda Cold Dark Matter (ΛCDM) is now the standard theory of structure formation in the universe. We present the first results from the new Bolshoi dissipationless cosmological ΛCDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was run in a volume 250 h –1 Mpc on a side using ~8 billion particles with mass and force resolution adequate to follow subhalos down to the completeness limit of V circ = 50 km s–1 maximum circular velocity. Using merger trees derived from analysis of 180 stored time steps we find the circular velocities of satellites before they fall into their host halos. Using excellent statistics of halos and subhalos (~10 million at every moment and ~50 million over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, the abundance of halos as a function of their circular velocity, and the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum value of about 4.0 and then rises for higher values of halo mass—a new result. We present approximations for the velocity and mass functions of distinct halos as a function of redshift. We find that while the Sheth-Tormen (ST) approximation for the mass function of halos found by spherical overdensity is quite accurate at low redshifts, the ST formula overpredicts the abundance of halos by nearly an order of magnitude by z = 10. We find that the number of subhalos scales with the circular velocity of the host halo as V 1/2 host, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function N(> V sub) scales as V –3 circ. Combining the results of Bolshoi and Via Lactea-II simulations, we find that inside the virial radius of halos with the number of satellites is N(> V sub) = (V sub/58 km s–1)–3 for satellite circular velocities in the range 4 km s–1 < V sub < 150 km s–1.
   
   
2. arXiv.org > astro-ph > arXiv:1005.1289
   LCDM Correctly Predicts Basic Statistics of Galaxies: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, and Velocity Function S. Trujillo-Gomez, A. Klypin, J. Primack, A. Romanowsky
   [abs, pdf, ps, other]
   
   It has long been regarded as difficult if not impossible for a cosmological model to account simultaneously for the galaxy luminosity, mass, and velocity distributions. Using a compilation of observational data along with high resolution large-scale cosmological simulation of dark matter, we find that the standard cosmological model fits - at least on average - all basic statistics of galaxies with circular velocities Vc>50km/s calculated at 10kpc radius. Besides an SDSS-based r-band luminosity function, our primary observational constraint is the luminosity-velocity relation that includes all types of galaxies from dwarf irregulars to giant ellipticals. The data present a clear monotonic luminosity-velocity relation for Vc=50-500km/s, with a bend below 80km/s and a bimodality between late- and early-type galaxies. We also use of the LCDM Bolshoi cosmological simulation. An abundance-matching technique is used to assign rank-ordered galaxy luminosities to the dark matter halos, a procedure which automatically fits the empirical luminosity function and provides a predicted luminosity-velocity relation that can be checked against observations. The resulting predictions for the luminosity-velocity relation are in good agreement with the available data on both early-type and late-type galaxies for the magnitude range Mr=-14 -22. We also compare our predictions for the cold baryon mass of galaxies as a function of circular velocity with the available observations, again finding good agreement except perhaps at the highest Vc. The predicted circular velocity function is in agreement with the galaxy velocity function for Vc=80-400km/s. However, in agreement with other recent results, we find that the dark matter halos with Vc <50km/s are much more abundant than observed galaxies.
   
   
3. arXiv.org > astro-ph > arXiv:1011.2203
   The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds
   Michael T. Busha (Stanford Univeristy/Univeristy of Zurich), Philip J. Marshall (Stanford University/University of Oxford), Risa H. Wechsler (Stanford University), Anatoly Klypin (New Mexico State University), Joel Primack (UCSC)
   [abs, pdf, ps, other]
   
   (Submitted on 9 Nov 2010 (v1), last revised 11 Nov 2010 (this version, v2))
   We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a LambdaCDM universe. A large, high resolution cosmological simulation of this universe provides a means to statistically sample the dynamical properties of bright satellite galaxies in a large population of dark matter halos. The observed properties of the MCs, including their circular velocity, distance from the center of the MW, and velocity within the MW halo, are used to evaluate the likelihood that a given halo would have each or all of these properties; the posterior PDF for any property of the MW system can thus be constructed. This method provides a constraint on the MW virial mass, 1.2(+0.7-0.4)e12 Msun (68% confidence), which is consistent with recent determinations that involve very different assumptions. In addition, we calculate the posterior PDF for the density profile of the MW and its satellite accretion history. Although typical satellites of 1e12 Msun halos are accreted over a wide range of epochs over the last 10 Gyr, we find a 72% probability that the Magellanic Clouds were accreted within the last Gyr, and a 50% probability that they were accreted together.


4. Statistics of Satellite Galaxies Around Milky Way-Like Host Michael T. Busha, Risa H.Wechsler, Peter S. Behroozi, Brian F. Gerke, Anatoly A. Klypin, Joel R. Primack
   [abs, pdf, ps, other]
   
   We calculate the probability that a Milky-Way-like halo in the standard cosmological model has the observed number of Magellanic Clouds (MCs). The statistics of the number of MCs in the LCDM model are in good agreement with observations of a large sample of SDSS galaxies. Under the sub-halo abundance matching assumption of a relationship with small scatter between galaxy r-band luminosities and halo internal velocities, vmax, we make detailed comparisons to similar measurements using SDSS DR7 data by Liu et al 2010. Models and observational data give very similar probabilities for having zero, one, and two MC-like satellites. In both cases, Milky Way-luminosity hosts have just a ~10% chance of hosting two satellites similar to the Magellanic Clouds. In addition, we present a prediction for the probability for a host galaxy to have N satellite galaxies as a function of the magnitudes of both the host and satellite. This probability and its scaling with host properties is significantly different from that of mass-selected objects because of scatter in the mass-luminosity relation and because of variations in the star formation efficiency with halo mass.
   
   
5. arXiv.org > astro-ph > arXiv:1104.5130
   Halo concentrations in the standard LCDM cosmology
   Francisco Prada, Anatoly A. Klypin, Antonio J. Cuesta, Juan E. Betancort-Rijo, Joel Primack
   [abs, pdf, ps, other]
   
   We study the concentration of dark matter halos and its evolution in N-body simulations of the standard LCDM cosmology. The results presented in this paper are based on 4 large N-body simulations with about 10 billion particles each: the Millennium-I and II, Bolshoi, and MultiDark simulations. The MultiDark (or BigBolshoi) simulation is introduced in this paper. This suite of simulations with high mass resolution over a large volume allows us to compute with unprecedented accuracy the concentration over a large range of scales (about six orders of magnitude in mass), which constitutes the state-of-the-art of our current knowledge on this basic property of dark matter halos in the LCDM cosmology. We find that there is consistency among the different simulation data sets. We confirm a novel feature for halo concentrations at high redshifts: a flattening and upturn with increasing mass. The concentration c(M,z) as a function of mass and the redshift and for different cosmological parameters shows a remarkably complex pattern. However, when expressed in terms of the linear rms fluctuation of the density field sigma(M,z), the halo concentration c(sigma) shows a nearly-universal simple U-shaped behaviour with a minimum at a well defined scale at sigma=0.71. Yet, some small dependences with redshift and cosmology still remain. At the high-mass end (sigma < 1) the median halo kinematic profiles show large signatures of infall and highly radial orbits. This c-sigma(M,z) relation can be accurately parametrized and provides an analytical model for the dependence of concentration on halo mass. When applied to galaxy clusters, our estimates of concentrations are substantially larger -- by a factor up to 1.5 -- than previous results from smaller simulations, and are in much better agreement with results of observations. (abridged)
   
   
6. arXiv.org > astro-ph > arXiv:1109.0003
   The MultiDark Database: Release of the Bolshoi and MultiDark Cosmological Simulations Kristin Riebe, Adrian M. Partl, Harry Enke, Jaime Forero-Romero, Stefan Gottloeber, Anatoly Klypin, Gerard Lemson, Francisco Prada, Joel R.
   Primack, Matthias Steinmetz, Victor Turchaninov
   [abs, pdf, other]
   
   We present the online MultiDark Database – a Virtual Observatory-oriented, relational database for hosting various cosmological simulations. The data is accessible via an SQL (Structured Query Language) query interface, which also allows users to directly pose scientific questions, as shown in a number of examples in this paper. Further examples for the usage of the database are given in its extensive online documentation. The database is based on the same technol- ogy as the Millennium Database, a fact that will greatly facilitate the usage of both suites of cosmological simulations. The first release of the MultiDark Database hosts two 8.6 billion particle cosmological N-body simulations: the Bolshoi (250 h−1Mpc simulation box, 1 h−1kpc resolution) and MultiDark Run1 simulation (MDR1, or BigBolshoi, 1000h−1Mpc simulation box, 7h−1kpc resolution). The extraction methods for halos/subhalos from the raw simulation data, and how this data is structured in the database are explained in this paper. With the first data release, users get full access to halo/subhalo catalogs, various profiles of the halos at redshifts z = 0 − 15, and raw dark matter data for one time-step of the Bolshoi and four time-steps of the MultiDark simulation. Later releases will also include galaxy mock catalogs and additional merging trees for both simulations as well as new large volume simulations with high resolution. This project is further proof of the viability to store and present complex data using relational database technology. We encourage other simulators to publish their results in a similar manner.
   
   
   
7. arXiv.org > astro-ph > arXiv:1110.4372
   The Rockstar Phase-Space Temporal Halo Finder and the Velocity Offsets of Cluster Cores Peter S. Behroozi, Risa H. Wechsler, Hao-Yi Wu
   [abs, pdf, other]
   
   We present a new algorithm for identifying dark matter halos, substructure, and tidal features. The approach is based on adaptive hierarchical refinement of friends-of-friends groups in six phase-space dimensions and one time dimension, which allows for robust (grid-independent, shape-independent, and noise-resilient) tracking of substructure; as such, it is named Rockstar (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement). Our method is massively parallel (up to 10^5 CPUs) and runs on the largest current simulations (>10^10 particles) with high efficiency (10 CPU hours and 60 gigabytes of memory required per billion particles analyzed). A previous paper (Knebe et al 2011) has shown Rockstar to have class-leading recovery of halo properties; we expand on these comparisons with more tests and higher-resolution simulations. We show a significant improvement in substructure recovery as compared to several other halo finders and discuss the theoretical and practical limits of simulations in this regard. Finally, we present results which demonstrate conclusively that dark matter halo cores are not at rest relative to the halo bulk or satellite average velocities and have coherent velocity offsets across a wide range of halo masses and redshifts. For massive clusters, these offsets can be up to 400 km/s at z=0 and even higher at high redshifts. Our implementation is publicly available at this http URL .
   
   
8. Gravitationally Consistent Halo Catalogs and Merger Trees for Precision Cosmology
   Peter S. Behroozi, Risa H. Wechsler, Hao-Yi Wu, Michael T. Busha, Anatoly Klypin, Joel Primack.
   [abs, pdf, other]
   
   We present a new algorithm for generating merger trees and halo catalogs which explicitly ensures consistency of halo properties (mass, position, velocity, radius) across timesteps. Our algorithm has demonstrated the ability to improve both the completeness (through detecting and inserting otherwise missing halos) and purity (through detecting and removing spurious objects) of both merger trees and halo catalogs. In addition, our method is able to robustly measure the self-consistency of halo finders; it is the first to directly measure the uncertainties in halo positions, halo velocities, and the halo mass function for a given halo finder based on consistency between snapshots in cosmological simulations. We use this algorithm to generate merger trees for two large simulations (Bolshoi and Consuelo) and evaluate two halo finders (ROCKSTAR and BDM). We find that both the ROCKSTAR and BDM halo finders track halos extremely well; in both, the number of halos which do not have physically consistent progenitors is at the 1-2% level across all halo masses. Our code is publicly available at this http URL . Our trees and catalogs will made publicly available once the referee process is complete.