Great Plains Cosmology Workshop

October 26-27, 2001

University of Kansas, Lawrence KS

9:30-10:00 Sergei Kopeikin (MU)
Cosmological perturbations: a new gauge-invariant approach
10:00-10:30 Adrian Melott (KU)
Discreteness and Collision Error: the N-body Skeleton in the Closet
10:30-11:00 Jim Fry (UFL)
The Nonlinear Kinetic Sunayev-Zel'dovich Effect
11:00-11:30 Chris Miller (CMU)
Nonparametric Function Estimation and Cosmological Applications
11:30-12:00 Patrick M Motl (MU)
A New Picture of Galaxy Cluster Cooling Cores: Formation via Hierarchical Mergers
12:00-1:30 Lunch
1:30-2:00 Sergei Shandarin (KU)
Gaussianity of the CMB Maps
2:00-2:30 Pia Mukherjee (KSU)
Galactic Foregrounds in Microwave Data
2:30-3:00 Hume Feldman (KU)
Optimal Moments for the Analysis of Peculiar Velocity Surveys
3:00-3:30 Coffee
3:30-4:00 Will Chambers (KU)
Cosmological Clues from Rich Galaxy Cluster Shape Parameters
4:00-4:30 Roman Juszkiewicz (CAMK & KU)
Evidence for low $\Omega_m$ from relative motions of galaxy pairs: Mark III vs. SFI data.
4:30-5:00 Nurur Rahman (KU)
The Cluster Mass Function to Constrain Cosmological Models


Patrick M Motl

A New Picture of Galaxy Cluster Cooling Cores: Formation via Hierarchical Mergers

New state of the art large-scale structure simulations have suggested a novel scenario for the formation of cooling cores in rich clusters. We find that cores of cool gas, material that would be identified as a classical cooling flow based upon its X-Ray luminosity excess and temperature profile, are built from the accretion of discrete, stable subclusters. Any ``cooling flow'' present is overwhelmed by the velocity field within the cluster. Thus, the inclusion of consistent initial cosmological conditions for the cluster within its surrounding environment is crucial when attempting to address the evolution of cooling cores in rich galaxy clusters. This new model for the hierarchical assembly of cooling cores naturally explains the high frequency of these cores in rich galaxy clusters despite the fact that a majority of rich clusters also show evidence of substructure which is believed to arise from recent merger activity. Also, complex filamentary structures of cool gas in our simulations appear similar to those seen in recent Chandra observations. Our simulations were computed with a coupled N-body, Eulerian AMR hydrodynamics cosmology code that properly treats the effects of radiative cooling by the gas. We employ seven levels of refinement to attain a peak resolution of 15.6 $\mathrm{h}^{-1}$ kpc within a volume 256 $\mathrm{h}^{-1}$ Mpc on a side and assume a standard $\Lambda$CDM cosmology.


Chris Miller

Nonparametric Function Estimation and Cosmological Applications

We present a new statistical technique to nonparametrically estimate an underelying function from noisy data. The method was developed by Beran (2000) and is named REACT for: Risk Estimation, Adaption, and Coordinate Transformation. There are significant advantages for using this technique: (1) The nonparametric fit is optimized to the data and errors in hand by minimizing the variance and the statistical bias; (2) REACT returns a confidence "radius" which allows one to place valid confidence intervals around any interesting quantity for the underlying function. This is not possible with stantard $\chi^2$ techniques or Bayesian methods; (3) REACT can be generalized to work with correlated errors. We apply the REACT technique to the CMB temperature power spectrum. We also discuss the many areas of research where nonparametric techiques can be uesful.


Sergei Kopeikin

Cosmological perturbations: a new gauge-invariant approach

A new gauge-invariant approach for describing cosmological perturbations is developed. It is based on a physically motivated splitting of the stress-energy tensor of the perturbation into two parts - the bare perturbation and the complementary perturbation associated with stresses in the background gravitational field induced by the introduction of the bare perturbation. The complementary perturbation of the stress-energy tensor is explicitly singled out and taken to the left side of the perturbed Einstein equations so that the bare stress-energy tensor is the sole source for the perturbation of the metric tensor and both sides of these equations are gauge invariant with respect to infinitesimal coordinate transformations. For simplicity we analyze the perturbations of the spatially-flat Friedmann-Lemaitre-Robertson-Walker dust model. A cosmological gauge can be chosen such that the equations for the perturbations of the metric tensor are completely decoupled for the $h_{00}$, $h_{0i}$, and $h_{ij}$ metric components and explicitly solvable in terms of retarded integrals.


Pia Mukherjee

Galactic Foregrounds in Microwave Data:

A study of Galactic foregrounds in microwave data so far doesnt contradict the hypothesis that there are two dust-correlated components of emission present in CMB data, namely free-free emission and spinning dust emission. More needs to be known before we can reliably identify and separate these from CMB data.


Will Chambers

Cosmological Clues from Rich Galaxy Cluster Shape Parameters

Galaxy clusters are often elongated structures. This allows one to assign orientations and ellipticities. Important cosmological information can be inferred from these rather simple shape parameters. For example, they can be used to (1) support the gravitational instability hypothesis of large-scale structure formation (2) discriminate between low and high cosmological mass densities (3) infer the dynamical state of a cluster. I will discuss recent research done at the Univ. of Kansas in these areas.


Roman Juszkiewicz

Evidence for low $\Omega_m$ from relative motions of galaxy pairs: Mark III vs. SFI data.

The mean relative velocity of galaxy pairs, $v_{12}(r)$, can be used to estimate $\Omega_m$ from redshift-distance galaxy surveys. I will describe some preliminary results we obtained with Hume Feldman last week.


Adrian L. Melott

Discreteness and Collision Error: the N-body Skeleton in the Closet

Two-body scattering and other discreteness effects are unimportant in cosmological gravitational clustering in most scenarios, since the dark matter has a small particle mass. The collective field should determine evolution: Two-body scattering in simulations violates the Poisson-Vlasov equations. We test this in PM, P$^3$M, Tree, and NGPM codes, noting that a collisionless code will preserve the one-dimensional character of plane wave collapse. We find collisionality vanishing as the softening parameter approaches the mean interparticle separation. This calls into question nearly all results on small scales in cosmological clustering simulations. Solutions for the problem are suggested, involving greater computer power, PM-based nested grid codes, and a more conservative approach to resolution claims.


Hume Feldman

Optimal Moments for the Analysis of Peculiar Velocity Surveys

We present a new method for the analysis of peculiar velocity surveys which removes contributions to velocities from small scale, nonlinear velocity modes while retaining information about large scale motions. Our method utilizes Karhunen-Loève methods of data compression to construct a set of moments out of the velocities which are minimally sensitive to small scale power. The set of moments are then used in a likelihood analysis. We develop criteria for the selection of moments, as well as a statistic to quantify the overall sensitivity of a set of moments to small scale power. Although we discuss our method in the context of peculiar velocity surveys, it may also prove useful in other situations where data filtering is required.


Jim Fry

The Nonlinear Kinetic Sunyaev-Zel'dovich Effect

The kinetic Sunyaev-Zel'dovich effect (anisotropy in the cosmic microwave background induced by scattering off ionized matter in bulk motion) has significant contributions from nonlinearly evolved scales. I present general expressions for the fully nonlinear angular power and specific results evaluated in the halo model of nonlinear clustering.


Nurur Rahman

The Cluster Mass Function to Constrain Cosmological Models

Cluster abundance test puts stringent constraints on the models of the structure formation. This test can constrain cosmological parameters such as matter density ( $\Omega_0 = \Omega_b + \Omega_{cdm} +
\Omega_{hdm}$) in the Universe and the amplitude of the mass density fluctuations ($\sigma_8$). We present a comparison between two observational and three theoretical mass functions for eight cosmological best-fit models suggested by the data from recently the completed BOOMERANG-98, MAXIMA-1 cosmic microwave background (CMB) anisotropy experiments as well as peculiar velocities (PVs) and type Ia supernovae (SN) observations. We notice that models are in general show disagreement with the abundances of X-ray clusters at $\sim
10^{14.7} h^{-1}M_{\odot}$. On the hand, we notice that several models such as, the BOOM+MAX+COBE:I, Refined Concordance and $\Lambda$MDM are in a good agreement with the abundances of optical clusters. The P11 and especially Concordance models predict a slightly lower abundances than observed at $\sim 10^{14.6} h^{-1}M_{\odot}$. The BOOM+MAX+COBE:II and PV+CMB+SN models predict a slightly higher abundances than observed at $\sim 10^{14.9} h^{-1}M_{\odot}$. The nonflat MAXIMA-1 is in a fatal conflict with the observational cluster abundances and can be safely ruled out. Our analysis justifies the present notion of the low matter density ( $\Omega_0 \sim 0.40 $) Universe dominated by the some unknown dark energy density ( $\Omega_{\Lambda} \sim 0.60$).




Hume Feldman
Last modified: Sat Oct 27 15:45:32 MET DST 2001