Simultaneous Falsification Of Λcdm And Quintessence With Massive, Distant Clusters

Preprint typeset in JHEP style - HYPER VERSION

Testing cosmological models using relative mass-redshift abundance of SZ clusters
Arman Shafieloo

arXiv:1109.4483v1 [astro-ph.CO] 21 Sep 2011

Institute for the Early Universe, Ewha Womans University Seoul, 120-750, South Korea E-mail: arman@ewha.ac.kr

George F. Smoot
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA andInstitute for the Early Universe, Ewha Womans University Seoul, 120-750, South Korea and Paris Centre for Cosmological Physics, Universite Paris Diderot, France E-mail: gfsmoot@lbl.gov

Abstract: Recent detection of high-redshift, massive clusters through SunyaevZel’dovich observations has opened up a new way to test cosmological models. It is known that detection of a single supermassive cluster ata very high redshift can rule out many cosmological models all together. However, since dealing with different observational biases makes it difficult to test the likeliness of the data assuming a cosmological model, most of the cluster data (except those with high mass-redshift) stays untouched in confronting cosmological models with cluster observations. We propose here that one can use therelative abundance of the clusters with different masses at different redshifts to test the likeliness of the data in the context of cosmological models. For this purpose we propose a simple parametric form for the efficiency of observing clusters at different mass-redshift and we test if the standard ΛCDM model can explain the observed abundance of the clusters using this efficiency parameterization. We arguethat one cannot expect an unusual and highly parametric form of the efficiency function to fit the observed data assuming a theoretical model. Using many realizations of Monte Carlo simulations we show that the standard spatially flat ΛCDM model is barely consistent with the SPT cluster data using a simple and plausible two-dimensional efficiency function for detection of the clusters. More clusterdata are needed to make any strong conclusion. Keywords: SZ Clusters, Cosmological model selection.

Contents
1. Introduction 2. Data and Theoretical Expectations 3. Detection Efficiency 4. Likelihood Analysis and simulations 5. Results 6. Conclusion 1 3 5 8 12 15

1. Introduction
A key task of modern cosmology is to determine the actual model of the universe and its parameters. There have beenmany efforts in last two decades using various observations to distinguish between cosmological models and put constraints on some of the key cosmological quantities like matter density, curvature and dark energy. Cosmic microwave background (CMB), supernovae type Ia, large scale structure of the universe and distribution of the galaxies and weak/strong gravitational lensing have been so far themain sources of information for cosmologists to probe and study the universe. However, with higher quality data, advancements in computational analysis, and more sophisticated statistical techniques, we can look for more observational sources from our surrounding universe to study the cosmos. Recent developments in CMB observations provides us with high angular resolution, large area mapping, whichcan be used to detect massive clusters up to very high redshifts through the Sunyaev-Zel’dovich (SZ) effect [1]. Clusters can be a strong discriminator against or among cosmological models. It takes time for the universe to become a host for massive clusters of galaxies so the time (redshift) that clusters appear in the universe is important. The predicted distribution of the mass of clusters withredshift is related to the assumed theoretical model and also the initial conditions for the primordial fluctuations. Hence observations of massive clusters at different redshifts can be used to test different cosmological models. For instance, detection of a single supermassive cluster above a

–1–

certain redshift can simply rule out those cosmological models that do not and cannot predict...