Laura Elizabeth Grego

Determining the Cosmic Distance Scale from Interferometric Measurements of the Sunyaev-Zeldovich Effect

We determine the distances to 18 galaxy clusters with redshifts ranging from z ~ 0.14 to 0.78 from a maximum likelihood joint analysis of 30 GHz interferometric Sunyaev-Zeldovich effect (SZE) and X-ray observations. We model the intracluster medium (ICM) using a spherical isothermal β model. We quantify the statistical and systematic uncertainties inherent to these direct distance measurements, and we determine constraints on the Hubble parameter for three different cosmologies. These distances imply a Hubble constant of 60 km s-1 Mpc-1 for an ΩM = 0.3, ΩΛ = 0.7 cosmology, where the uncertainties correspond to statistical followed by systematic at 68% confidence. With a sample of 18 clusters, systematic uncertainties clearly dominate. The systematics are observationally approachable and will be addressed in the coming years through the current generation of X-ray satellites (Chandra and XMM-Newton) and radio observatories (Owens Valley Radio Observatory, Berkeley-Illinois-Maryland Association, and Very Large Array). Analysis of high-redshift clusters detected in future SZE and X-ray surveys will allow a determination of the geometry of the universe from SZE-determined distances.

Galaxy Cluster Gas Mass Fractions from Sunyaev-Zeldovich Effect Measurements: Constraints on ΩM

Using sensitive centimeter-wave receivers mounted on the Owens Valley Radio Observatory and Berkeley-Illinois-Maryland-Association millimeter arrays, we have obtained interferometric measurements of the Sunyaev-Zeldovich (SZ) effect toward massive galaxy clusters. We use the SZ data to determine the pressure distribution of the cluster gas and, in combination with published X-ray temperatures, to infer the gas mass and total gravitational mass of 18 clusters. The gas mass fraction, fg, is calculated for each cluster and is extrapolated to the fiducial radius r500 using the results of numerical simulations. The mean fg within r500 is 0.081 h (statistical uncertainty at 68% confidence level, assuming ΩM = 0.3, ΩΛ = 0.7). We discuss possible sources of systematic errors in the mean fg measurement. We derive an upper limit for ΩM from this sample under the assumption that the mass composition of clusters within r500 reflects the universal mass composition: ΩMh ≤ ΩB/fg. The gas mass fractions depend on cosmology through the angular diameter distance and the r500 correction factors. For a flat universe (ΩΛ ≡ 1 - ΩM) and h = 0.7, we find the measured gas mass fractions are consistent with ΩM < 0.40, at 68% confidence. Including estimates of the baryons contained in galaxies and the baryons which failed to become bound during the cluster formation process, we find ΩM ~ 0.25.

Evolution of the Cluster X-Ray Scaling Relations since z > 0.4

We derive correlations between X-ray temperature, luminosity, and gas mass for a sample of 22 distant, z>0.4, galaxy clusters observed with Chandra. We detect evolution in all three correlations between z>0.4 and the present epoch. In particular, in the Omega=0.3, Lambda=0.7 cosmology, the luminosity corresponding to a fixed temperature scales approximately as (1+z)**(1.5+-0.3); the gas mass for a fixed luminosity scales as (1+z)**(-1.8+-0.4); and the gas mass for a fixed temperature scales as (1+z)**(-0.5+-0.4) (all uncertainties are 90% confidence). We briefly discuss the implication of these results for cluster evolution models.

Sunyaev-Zeldovich Effect-derived Distances to the High-Redshift Clusters MS 0451.6–0305 and Cl 0016+16

We determine the distances to the z approximately equals 0.55 galaxy clusters MS 0451.6 - 0305 and Cl 0016 + 16 from a maximum-likelihood joint fit to interferometric Sunyaev-Zeldovich effect (SZE) and X-ray observations. We model the intracluster medium (ICM) using a spherical isothermal beta model. We quantify the statistical and systematic uncertainties inherent to these direct distance measurements, and we determine constraints on the Hubble parameter for three different cosmologies. For an Omega(sub M) = 0.3, Omega(sub lambda) = 0.7 cosmology, these distances imply a Hubble constant of 63(sup +12) (sub -9) (sup + 21) (sub -21) km/s Mp/c, where the uncertainties correspond to statistical followed by systematic at 68% confidence. The best-fit H(sub 0) is 57 km/s Mp/c for an open (Omega(sub M) = 0.3) universe and 52 km/s Mp/c for a flat (Omega(sub M) = 1) universe.

Chandra X-Ray Detection of the Radio Hot Spots of 3C 295

An observation of the radio galaxy 3C 295 during the calibration phase of the Chandra X-Ray Observatory reveals X-ray emission from the core of the galaxy, from each of the two prominent radio hot spots, and from the previously known cluster gas. We discuss the possible emission processes for the hot spots and argue that a synchrotron self-Compton (SSC) model is preferred for most or all of the observed X-ray emission. SSC models with near-equipartition fields thus explain the X-ray emission from the hot spots in the two highest surface brightness FR II radio galaxies, Cygnus A and 3C 295. This lends weight to the assumption of equipartition and suggests that relativistic protons do not dominate the particle energy density.

The Sunyaev-Zeldovich Effect in Abell 370

We present interferometric measurements of the Sunyaev-Zeldovich (SZ) eUect toward the galaxy cluster Abell 370. These measurements, which directly probe the pressure of the clusters gas, show the gas distribution to be strongly aspherical, as do the X-ray and gravitational lensing observations. We calculate the clusters gas mass fraction in two ways. We —rst compare the gas mass derived from the SZ measurements to the lensing-derived gravitational mass near the critical lensing radius. We also calculate the gas mass fraction from the SZ data by deprojecting the three-dimensional gas density distribution and deriving the total mass under the assumption that the gas is in hydrostatic equilibrium (HSE). We test the assumptions in the HSE method by comparing the total cluster mass implied by the two methods and —nd that they agree within the errors of the measurement. We discuss the possible system- atic errors in the gas mass fraction measurement and the constraints it places on the matter density parameter, ) M. Subject headings: cosmic microwave backgroundcosmology: observations ¨ galaxies: clusters: individual (Abell 370) ¨ techniques: interferometric

Limits on Arcminute-Scale Cosmic Microwave Background Anisotropy at 28.5 GHz

We have used the Berkeley-Illinois-Maryland-Association (BIMA) millimeter array outfitted with sensitive cm-wave receivers to search for Cosmic Microwave Background (CMB) anisotropies on arcminute scales. The interferometer was placed in a compact configuration which produces high brightness sensitivity, while providing discrimination against point sources. Operating at a frequency of 28.5 GHz, the FWHM primary beam of the instrument is 6.6 arcminutes. We have made sensitive images of seven fields, five of which where chosen specifically to have low IR dust contrast and be free of bright radio sources. Additional observations with the Owens Valley Radio Observatory (OVRO) millimeter array were used to assist in the location and removal of radio point sources. Applying a Bayesian analysis to the raw visibility data, we place limits on CMB anisotropy flat-band power Q_flat = 5.6 (+3.0, -5.6) uK and Q_flat < 14.1 uK at 68% and 95% confidence. The sensitivity of this experiment to flat band power peaks at a multipole of l = 5470, which corresponds to an angular scale of approximately 2 arcminutes The most likely value of Q_flat is similar to the level of the expected secondary anisotropies.

Investigation of Two Reported Arcminute-Scale Microwave Decrements at 28.5 GHz

Recently, Jones et al. (1997) used the Ryle telescope, operating at a frequency of 15 GHz, to detect a flux decrement in the direction of the quasar pair PC1643+461A,B. They interpreted this signal as the Sunyaev-Zel’dovich effect (SZE) produced by a distant cluster of galaxies. In the course of an effort to measure CMB anisotropies using the VLA at 8.4 GHz, Richards et al. (1997) detected a similar, but smaller, decrement which we refer to as VLA1312+4237. They also proposed that this signal might be explained as the SZE signal of a distant galaxy cluster. We report observations in the direction of these claimed sources with the Berkeley Illinois Maryland Association (BIMA) interferometer operating at 28.5 GHz. We find no evidence for SZE emission in the direction of either of the claimed sources. In the case of PC1643+4631, the BIMA data are inconsistent with the cluster emission model proposed by Jones et al. (1997) at greater than 99.99% confidence. Together with published x-ray and optical searches, these results make a compelling case against the existence of a massive cluster in the direction of PC1643+4631. Because of the different scales to which the VLA and BIMA instruments are sensitive, the BIMA observations are not as constraining for the VLA1312+4237 source. The BIMA data are inconsistent with the cluster model proposed by Richards et al. (1997) at ∼ 80% confidence. Subject headings: cosmology: observation — cosmic microwave background — galaxies: clusters — techniques: interferometric Department of Physics, University of California, Berkeley, CA 94720 Department of Astronomy, University of Chicago, Chicago IL 60637 Harvard-Smithsonian Center for Astrophysics, Mail Stop 83, 60 Gardeen St., Cambridge MA 02138 Space Science Laboratory, SD50, NASA Marshall Space Flight Center, Huntsville AL 35812 Department of Physics, University of Alabama, Huntsville AL 35899The Ryle telescope has been used at a frequency of 15 GHz, to detect a flux decrement in the direction of the quasar pair PC 1643+4631A, B. This signal was interpreted as the Sunyaev-Zeldovich effect (SZE) produced by a distant cluster of galaxies. In the course of an effort to measure cosmic microwave background (CMB) anisotropies with a deep pointing of the VLA at 8.4 GHz, a second group detected a similar, but smaller, decrement. They also proposed that this signal might be explained as the SZE signal produced by a distant galaxy cluster. We report observations with the Berkeley-Illinois-Maryland Association (BIMA) interferometer operating at 28.5 GHz, in which we find no evidence for a SZE signal in the direction of either of the proposed clusters. In the case of the Ryle detection, the BIMA data are inconsistent with the SZE model proposed to explain the observed decrement at greater than 99.99% confidence. Together with published X-ray and optical searches, these results make a compelling case against the interpretation of the Ryle decrement as being due to the SZE in a massive cluster of galaxies. For the smaller VLA source, the BIMA observations are not as constraining. The BIMA data are inconsistent with the proposed SZE model at greater than 90% confidence.