Chandra's First Decade of Discovery

Session 7: Galaxy Clusters - Cosmology

Studies of Dark Energy with Chandra

Alexey Vikhlinin, SAO

I will review Chandra's contribution to studies of Dark Energy. Observable effects of Dark Energy fall into two broad classes, its effect on the expansion rate as a function of time, and on the rate of growth of cosmic structures; Chandra has detected and measured both through observations of galaxy clusters. Combination with other cosmological datasets leads to 5% constraints on the Dark Energy equation of state, and limits possible deviations of gravity on large scales from General Relativity.

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Chandra and SZA Observations of Clusters of Galaxies at z>1

Thomas Culverhouse, University of Chicago
Stefano Andreon (OAB Milano), Esra Bulbul (UA Huntsville), Max Bonamente (UA Huntsville), Marshall Joy (NASA Marshall Space Flight Center), John Carlstrom (University of Chicago), Nicole Hasler (UA Huntsville), David Hawkins (Caltech Owens Valley Radio Observatory), Ryan Hennessy (University of Chicago), James Lamb (Caltech Owens Valley Radio Observatory), Erik Leitch (University of Chicago), Daniel Marrone (University of Chicago), Ben Maughan (University of Bristol), Amber Miller (Columbia University), Tony Mroczkowski (University of Penn), Stephen Muchovej (Caltech), Clem Pryke (University of Chicago), Matthew Sharp (University of Chicago), Adam Stanford (UC Davis), David Woody (Caltech Owens Valley Radio Observatory)

I will present Chandra X-ray and Sunyaev-Zeldovich Array (SZA) observations of a sample of galaxy clusters at high redshift (z>1). This regime remains relatively unexplored and yet holds the potential to tightly constrain cosmological models, provided the properties of the cluster population can be well calibrated. X-ray and Sunyaev-Zeldovich effect (SZE) measurements offer powerful and complementary probes of the hot gas in galaxy clusters; X-ray observations with Chandra allow detailed imaging and spectroscopy, while the SZE enables study of the gas out to larger radii on account of the weaker dependence of signal on gas density. Given the redshift independence of the SZE signal, the SZE is ideal for observing distant clusters. Using data from the SZA, a radio interferometer designed to image the SZE in galaxy clusters, constraints will be presented on the integrated Compton-y parameter, a measure of the total thermal energy in clusters. These new SZA measurements have produced high significance images of the SZE in several z>1 systems, including a cluster at z=1.39, the most distant system for which an SZE has been observed. Mass measurements calculated from Chandra observations, in conjunction with the SZA data, are used to compare the properties of our high redshift sample to scaling relations derived at lower redshift, to test for evidence of evolution.

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Cosmology Independent Measurement of the Gas Mass Fraction Using Chandra X-ray and Sunyaev-Zel'dovich Effect Measurements of High Redshift Clusters

Nicole Hasler, UA Huntsville
Esra Bulbul (UA Huntsville), Max Bonamente (UA Huntsville), Marshall Joy (NASA Marshall Space Flight Center), John Carlstrom (University of Chicago), Thomas Culverhouse (University of Chicago), David Hawkins (Caltech Owens Valley Radio Observatory), Ryan Hennessy (University of Chicago), James Lamb (Caltech Owens Valley Radio Observatory), Erik Leitch (University of Chicago), Daniel Marrone (University of Chicago), Amber Miller (Columbia University), Tony Mroczkowski (University of Penn), Stephen Muchovej (Caltech), Clem Pryke (University of Chicago), Matthew Sharp (University of Chicago), David Woody (Caltech Owens Valley Radio Observatory)

We present a joint Chandra and Sunyaev Zel'dovich Array (SZA) analysis method to determine the gas mass fraction independent of cosmology and demonstrate on Abell 2204. The advantage of using X-ray and Sunyaev Zel'dovich Effect observations is that it allows us to directly determine the angular diameter distance. We use a generalized form of the Navarro-Frenk-White (NFW) dark matter distribution together with a polytropic model for the hot plasma density, to determine an analytical solution for the density and temperature profiles. We then use these models to obtain the cluster mass of Abell 2204 using a Monte Carlo Markov Chain technique, and produce good fits at large radii. This is the first steps towards a measurement of the gas mass fraction as a function of redshift that can be used for the Allen et. al. (2008) method to constrain dark energy.

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Constraints on Cosmology and X-ray Scaling Relations from the Growth of Massive Galaxy Clusters

Adam Mantz, Stanford/SLAC
Steve Allen(1), David Rapetti(1), Harald Ebeling(2), Alex Drlica-Wagner(1); (1) Stanford/SLAC, (2) University of Hawaii

I will present simultaneous constraints on galaxy cluster X-ray scaling relations and cosmology obtained from observations of the growth of massive clusters. The data set consists of 238 flux-selected clusters at redshifts z ≤ 0.5 drawn from the ROSAT All-Sky Survey, and incorporates extensive Chandra follow-up observations. Our results on the scaling relations are consistent with excess heating of the intracluster medium; however, this heating appears to be limited to the central regions of clusters. The evolution of the scaling relations is consistent with the predictions of simple gravitational collapse models, indicating that the effects of excess heating on cluster properties do not evolve significantly within redshift 0.5. Clusters with cooling cores make up a significant fraction of our sample at all redshifts, consistent with most previous observations and with recent simulations. For spatially flat, constant-w cosmological models, the cluster data yield &Omegam = 0.23 ± 0.04, σ8 = 0.82 ± 0.05, and w = -1.01 ± 0.20, including conservative allowances for systematic uncertainties. Our results are consistent and competitive with a variety of independent cosmological data. In evolving-w models, marginalizing over transition redshifts in the range 0.05-1, the combination of the growth of structure data with the cosmic microwave background, supernovae, cluster gas mass fractions and baryon acoustic oscillations constrains the dark energy equation of state at late and early times to be respectively w0 = -0.88 ± 0.21 and wet = -1.05 +0.20-0.36. While our results on dark energy from the growth of structure alone are statistically limited at present, constraints from the combination with other cosmological data could be tightened by incorporating gravitational lensing observations and/or improved simulations of baryonic physics in clusters.

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Weighing the giants: X-ray and weak lensing studies measurements of the most massive clusters

Anja von der Linden, KIPAC/Stanford
Doug Applegate (KIPAC), Pat Kelly (KIPAC), Mark Allen (KIPAC), Steve Allen (KIPAC), Harald Ebeling (U Hawaii), Adam Mantz (KIPAC)

Chandra is a key instrument to understand the physics and evolution of galaxy clusters. But the combination with other high-quality, multi-wavelength observations is arguably even more powerful. We are conducting a multi-wavelength follow-up survey of ~30 of the most massive clusters known at z=0.3-0.6, selected from the MAssive Clusters Survey (MACS). Our follow-up data consists of Chandra X-ray imaging, deep multi-color imaging from SuprimeCam and HST imaging. The weak lensing mass measurements derived from the optical imaging will be a vital ingredient to determine the non-thermal pressure component in clusters, and thus to calibrate them as cosmological probes. At the same time, the multi-wavelength data allows us to study intriguing clusters in more detail, e.g. to study the physics of merging clusters. I will present our first results, and highlight some of the most intriguing clusters, such as the cousin of the Bullet Cluster, MACSJ0025.4-1222.

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