J. R. Bond

Excursion set mass functions for hierarchical Gaussian fluctuations

Most schemes for determining the mass function of virialized objects from the statistics of the initial density perturbation field suffer from the «cloud-in-cloud» problem of miscounting the number of low-mass clumps, many of which would have been subsumed into larger objects. We propose a solution based on the theory of the excursion sets of F(r, R f ), the four-dimensional initial density perturbation field smoothed with a continuous hierarchy of filters of radii Rf. We identify the mass fraction of matter in virialized objects with mass greater than M with the fraction of space in which the initial density contrast lies above a critical overdensity when smoothed on some filter of radius greater than or equal to R f (M).

The Santa Barbara Cluster Comparison Project: A Comparison of Cosmological Hydrodynamics Solutions

We have simulated the formation of an X-ray cluster in a cold dark matter universe using 12 different codes. The codes span the range of numerical techniques and implementations currently in use, including smoothed particle hydrodynamics (SPH) and grid methods with fixed, deformable, or multilevel meshes. The goal of this comparison is to assess the reliability of cosmological gasdynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be nonradiative. We compare images of the cluster at different epochs, global properties such as mass, temperature and X-ray luminosity, and radial profiles of various dynamical and thermodynamical quantities. On the whole, the agreement among the various simulations is gratifying, although a number of discrepancies exist. Agreement is best for properties of the dark matter and worst for the total X-ray luminosity. Even in this case, simulations that adequately resolve the core radius of the gas distribution predict total X-ray luminosities that agree to within a factor of 2. Other quantities are reproduced to much higher accuracy. For example, the temperature and gas mass fraction within the virial radius agree to within about 10%, and the ratio of specific dark matter kinetic to gas thermal energies agree to within about 5%. Various factors, including differences in the internal timing of the simulations, contribute to the spread in calculated cluster properties. Based on the overall consistency of results, we discuss a number of general properties of the cluster we have modeled.

Cosmology from MAXIMA-1, BOOMERANG, and COBE DMR Cosmic Microwave Background Observations

Recent results from BOOMERANG-98 and MAXIMA-1, taken together with COBE DMR, provide consistent and high signal-to-noise measurements of the cosmic microwave background power spectrum at spherical harmonic multipole bands over 2<l less similar to 800. Analysis of the combined data yields 68% (95%) confidence limits on the total density, Omega(tot) approximately 1.11+/-0.07 (+0.13)(-0.12), the baryon density, Omega(b)h(2) approximately 0.032(+0.005)(-0.004) (+0.009)(-0.008), and the scalar spectral tilt, n(s) approximately 1.01(+0.09)(-0.07) (+0.17)(-0.14). These data are consistent with inflationary initial conditions for structure formation. Taken together with other cosmological observations, they imply the existence of both nonbaryonic dark matter and dark energy in the Universe.

The Anisotropy of the microwave background to l = 3500: Mosaic observations with the Cosmic Background Imager

We report measurements of anisotropy in the cosmic microwave background radiation over the multipole range l 200 3500 with the Cosmic Background Imager based on deep observations of three fields. These results confirm the drop in power with increasing l first reported in earlier measurements with this instrument and extend the observations of this decline in power out to l 2000. The decline in power is consistent with the predicted damping of primary anisotropies. At larger multipoles, l 1⁄4 2000 3500, the power is 3.1 greater than standard models for intrinsic microwave background anisotropy in this multipole range and 3.5 greater than zero. This excess power is not consistent with expected levels of residual radio source contamination but, for 8e1, is consistent with predicted levels of a secondary Sunyaev-Zeldovich anisotropy. Further observations are necessary to confirm the level of this excess and, if confirmed, determine its origin. Subject headings: cosmic microwave background — cosmology: observations

Multiple peaks in the angular power spectrum of the cosmic microwave background: Significance and consequences for cosmology

Multiple Peaks in the Angular Power Spectrum of the Cosmic Microwave Background: Significance and Consequences for Cosmology arXiv:astro-ph/0105296 v1 17 May 2001 P. de Bernardis 1 , P.A.R. Ade 2 , J.J. Bock 3 , J.R. Bond 4 , J. Borrill 5 , A. Boscaleri 6 , K. Coble 7 , C.R. Contaldi 4 , B.P. Crill 8 , G. De Troia 1 , P. Farese 7 , K. Ganga 9 , M. Giacometti 1 , E. Hivon 9 , V.V. Hristov 8 , A. Iacoangeli 1 , A.H. Jaffe 10 , W.C. Jones 8 , A.E. Lange 8 , L. Martinis 11 , S. Masi 1 , P. Mason 8 , P.D. Mauskopf 12 , A. Melchiorri 13 , T. Montroy 7 , C.B. Netterfield 14 , E. Pascale 6 , F. Piacentini 1 , D. Pogosyan 4 , G. Polenta 1 , F. Pongetti 15 , S. Prunet 4 , G. Romeo 15 , J.E. Ruhl 7 , F. Scaramuzzi 11 Dipartimento di Fisica, Universita’ La Sapienza, Roma, Italy Queen Mary and Westfield College, London, UK Jet Propulsion Laboratory, Pasadena, CA, USA Canadian Institute for Theoretical Astrophysics, University of Toronto, Canada National Energy Research Scientific Computing Center, LBNL, Berkeley, CA, USA IROE-CNR, Firenze, Italy Dept. of Physics, Univ. of California, Santa Barbara, CA, USA California Institute of Technology, Pasadena, CA, USA IPAC, California Institute of Technology, Pasadena, CA, USA Department of Astronomy, Space Sciences Lab and Center for Particle Astrophysics, University of CA, Berkeley, CA 94720 USA ENEA, Frascati, Italy Dept. of Physics and Astronomy, Cardiff University, Cardiff CF24 3YB, Wales, UK Nuclear and Astrophysics Laboratory, University of Oxford, Keble Road, Oxford, OX 3RH, UK Depts. of Physics and Astronomy, University of Toronto, Canada Istituto Nazionale di Geofisica, Roma, Italy ABSTRACT Three peaks and two dips have been detected in the power spectrum of the cosmic microwave background from the BOOMERANG experiment, at ∼ 210, 540, 840 and ∼ 420, 750, respec- tively. Using model-independent analyses, we find that all five features are statistically significant and we measure their location and amplitude. These are consistent with the adiabatic inflation- ary model. We also calculate the mean and variance of the peak and dip locations and amplitudes in a large 7-dimensional parameter space of such models, which gives good agreement with the model-independent estimates, and forecast where the next few peaks and dips should be found if the basic paradigm is correct. We test the robustness of our results by comparing Bayesian marginalization techniques on this space with likelihood maximization techniques applied to a sec- ond 7-dimensional cosmological parameter space, using an independent computational pipeline, and find excellent agreement: Ω tot = 1.02 +0.06 vs. 1.04±0.05, Ω b h 2 = 0.022 −0.003 vs. 0.019 +0.005 , and n s = 0.96 −0.09 vs. 0.90±0.08. The deviation in primordial spectral index n s is a consequence of the strong correlation with the optical depth. Subject headings: Cosmic Microwave Background Anisotropy, Cosmology

Extended mosaic observations with the Cosmic Background Imager

Two years of microwave background observations with the Cosmic Background Imager (CBI) have been combined to give a sensitive, high-resolution angular power spectrum over the range 400 2000 power previously seen with the CBI is reduced. Under the assumption that any signal in excess of the primary anisotropy is due to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters, we use CBI, Arcminute Cosmology Bolometer Array Receiver, and Berkeley-Illinois-Maryland Association array data to place a constraint on the present-day rms mass fluctuation on 8 h-1 Mpc scales, σ8. We present the results of a cosmological parameter analysis on the l < 2000 primary anisotropy data that show significant improvements in the parameters as compared to WMAP alone, and we explore the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.

Cosmic confusion: degeneracies among cosmological parameters derived from measurements of microwave background anisotropies

ABSTRA C T In the near future, observations of the cosmic microwave background (CMB) anisotropies will provide accurate determinations of many fundamental cosmological parameters. In this paper, we analyse degeneracies among cosmological parameters to illustrate some of the limitations inherent in CMB parameter estimation. For simplicity, throughout our analysis we assume a cold dark matter universe with power-law adiabatic scalar and tensor fluctuation spectra. We show that most of the variance in cosmological parameter estimates is contributed by a small number (two or three) of principal components. An exact likelihood analysis shows that the usual Fisher matrix approach can significantly overestimate the errors on cosmological parameters. We show that small correlated errors in estimates of the CMB power spectrum at levels well below the cosmic variance limits (caused, for example, by Galactic foregrounds or scanning errors) can lead to significant biases in cosmological parameters. Estimates of cosmological parameters can be improved very significantly by applying theoretical restrictions to the tensor component, and external constraints derived from more conventional astronomical observations such as measurements of the Hubble constant, Type 1a supernovae distances and observations of galaxy clustering and peculiar velocities.

A Measurement of the CMB EE Spectrum from the 2003 Flight of BOOMERANG

We report measurements of the CMB polarization power spectra from the 2003 January Antarctic flight of BOOMERANG. The primary results come from 6 days of observation of a patch covering 0.22% of the sky centered near R.A. = 825, decl. = -45

A measurement of the angular power spectrum of the CMB temperature anisotropy from the 2003 flight of Boomerang

We report on observations of the cosmic microwave background (CMB) obtained during the 2003 January flight of BOOMERANG. These results are derived from 195 hr of observation with four 145 GHz polarization-sensitive bolometer (PSB) pairs, identical in design to the four 143 GHz Planck High Frequency Instrument (HFI) polarized pixels. The data include 75 hr of observations distributed over 1.84% of the sky with an additional 120 hr concentrated on the central portion of the field, which represents 0.22% of the full sky. From these data we derive an estimate of the angular power spectrum of temperature fluctuations of the CMB in 24 bands over the multipole range 50 ≤ l ≤ 1500. A series of features, consistent with those expected from acoustic oscillations in the primordial photon-baryon fluid, are clearly evident in the power spectrum, as is the exponential damping of power on scales smaller than the photon mean free path at the epoch of last scattering (l ≳ 900). As a consistency check, the collaboration has performed two fully independent analyses of the time-ordered data, which are found to be in excellent agreement.

Cosmological Parameters from Cosmic Background Imager Observations and Comparisons with BOOMERANG, DASI, and MAXIMA

We report on the cosmological parameters derived from observations with the Cosmic Background Imager (CBI), covering 40 deg2 and the multipole range 300 l 3500. The angular scales probed by the CBI correspond to structures that cover the mass range from 1014 to 1017 M?, and the observations reveal, for the first time, the seeds that gave rise to clusters of galaxies. These unique, high-resolution observations also show damping in the power spectrum to l ~ 2000, which we interpret as being due to the finite width of the photon-baryon decoupling region and the viscosity operating at decoupling. Because the observations extend to much higher l, the CBI results provide information complementary to that probed by the BOOMERANG, DASI, MAXIMA, and VSA experiments. When the CBI observations are used in combination with those from COBE-DMR, we find evidence for a flat universe, ?tot = 1.00 (1 ?), a power-law index of primordial fluctuations, ns = 1.08, and densities in cold dark matter, ?cdmh2 = 0.16, and baryons, ?bh2 = 0.023. With the addition of large-scale structure priors the ?cdmh2 value is sharpened to 0.10, and we find ?? = 0.67. In the l < 1000 overlap region with the BOOMERANG, DASI, MAXIMA, and VSA experiments, the agreement between these four experiments is excellent, and we construct optimal power spectra in the CBI bands that demonstrate this agreement. We derive cosmological parameters for the combined cosmic microwave background (CMB) experiments and show that these parameter determinations are stable as we progress from the weak priors using only CMB observations and very broad restrictions on cosmic parameters, through the addition of information from large-scale structure surveys, Hubble parameter determinations, and Type Ia supernova results. The combination of these with CMB observations gives a vacuum energy estimate of ?? = 0.70, a Hubble parameter of h = 0.69 ? 0.04, and a cosmological age of 13.7 ? 0.2 Gyr. As the observations are pushed to higher multipoles, no anomalies relative to standard models appear, and extremely good consistency is found between the cosmological parameters derived for the CBI observations over the range 610 < l < 2000 and observations at lower l.