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Register a new userConstraining cosmological parameters using Sunyaev-Zeldovich cluster surveys
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We discuss how future cluster surveys can constrain cosmological parameters with particular reference to the properties of the dark energy component responsible for the observed acceleration of the universe by probing the evolution of the surface density of clusters as a function of redshift. We explain how the abundance of clusters selected using their Sunyaev-Zeldovich effect can be computed as a function of the observed flux and redshift taking into account observational effects due to a finite beam-size. By constructing an idealized set of simulated observations for a fiducial model, we forecast the likely constraints that might be possible for a variety of proposed surveys which are assumed to be flux limited. We find that Sunyaev-Zeldovich cluster surveys can provide vital complementary information to those expected from surveys for supernovae. We analyse the impact of statistical and systematic uncertainties and find that they only slightly limit our ability to constrain the equation of state of the dark energy component.
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We discuss the prospects of constraining the properties of a dark energy component, with particular reference to a time varying equation of state, using future cluster surveys selected by their Sunyaev-Zeldovich effect. We compute the number of clusters expected for a given set of cosmological parameters and propogate the errors expected from a variety of surveys. In the short term they will constrain dark energy in conjunction with future observations of type Ia supernovae, but may in time do so in their own right.
Sunyaev Zeldovich cluster surveys can be used to constrain cosmological parameters. Extracting clusters from the primary anisotropies and the unresolved background from very faint clusters is simple when the telescope beam size is small (1 arcmin), but could be difficult if the beam is larger (8 arcmin). By reference to examples, we show that this is possible by carefully designing the depth of the survey.
We consider the optimum depth of a cluster survey selected using the Sunyaev-Zeldovich effect. By using simple models for the evolution of the cluster mass function and detailed modeling for a variety of observational techniques, we show that the optimum survey yield is achieved when the average size of the clusters selected is close to the size of the telescope beam. For a total power measurement, we compute the optimum noise threshold per beam as a function of the beam size and then discuss how our results can be used in more general situations. As a by-product we gain some insight into what is the most advantageous instrumental set-up. In the case of beam switching observations one is not severely limited if one manages to set the noise threshold close to the point which corresponds to the optimum yield. By defining a particular reference configuration, we show how our results can be applied to interferometer observations. Considering a variety of alternative scenarios, we discuss how robust our conclusions are to modifications in the cluster model and cosmological parameters. The precise optimum is particularly sensitive to the amplitude of fluctuations and the profile of the gas in the cluster.
Sensitive surveys of the Cosmic Microwave Background will detect thousands of galaxy clusters via the Sunyaev-Zeldovich (SZ) effect. Two SZ observables, the central or maximum and integrated Comptonization parameters y_max and Y, relate in a simple way to the total cluster mass, which allow the construction of mass functions (MFs) that can be used to estimate cosmological parameters such as Omega_M, sigma_8, and the dark energy parameter w. However, clusters form from the mergers of smaller structures, events that can disrupt the equilibrium of intracluster gas upon which SZ-M relations rely. From a set of N-body/hydrodynamical simulations of binary cluster mergers, we calculate the evolution of Y and y_max over the course of merger events and find that both parameters are transiently boosted, primarily during the first core passage. We then use a semi-analytic technique developed by Randall et al. (2002) to estimate the effect of merger boosts on the distribution functions YF and yF of Y and y_max, respectively, via cluster merger histories determined from extended Press-Schechter (PS) merger trees. We find that boosts do not induce an overall systematic effect on YFs, and the values of Omega_M, sigma_8, and w were returned to within 2% of values expected from the nonboosted YFs. The boosted yFs are significantly biased, however, causing Omega_M to be underestimated by 15-45%, sigma_8 to be overestimated by 10-25%, and w to be pushed to more negative values by 25-45%. We confirm that the integrated SZ effect, Y, is far more robust to mergers than y_max, as previously reported by Motl et al. (2005) and similarly found for the X-ray equivalent Y_X, and we conclude that Y is the superior choice for constraining cosmological parameters.
We review recent results of Sunyaev-Zeldovich effect (SZE) observations toward galaxy clusters. Using cm-wave receivers mounted on the OVRO and BIMA mm-wave arrays we have obtained high signal to noise images of the effect for more than 20 clusters. We present current estimates of the Hubble constant and cosmological parameters and discuss the potential of conducting statistical studies with large SZE cluster samples.
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