The Impact of Galaxy Cluster Mergers on Cosmological Parameter Estimation from Surveys of the SunyaevZel'dovich Effect
Abstract
Sensitive surveys of the cosmic microwave background will detect thousands of galaxy clusters via the SunyaevZel'dovich (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 allows the construction of mass functions (MFs) that can be used to estimate cosmological parameters such as Ω_{M}, σ_{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 on which SZ M relations rely. From a set of Nbody/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 semianalytic technique developed by Randall et al. 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 PressSchechter (PS) merger trees. We find that boosts do not induce an overall systematic effect on YFs, and the values of Ω_{M}, σ_{8}, and w were returned to within 2% of values expected from the nonboosted YFs. The boosted yFs are significantly biased, however, causing Ω_{M} to be underestimated by 15%45%, σ_{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. and similarly found for the Xray equivalent Y_{X}, and we conclude that Y is the superior choice for constraining cosmological parameters.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 2008
 DOI:
 10.1086/587790
 arXiv:
 arXiv:0802.3695
 Bibcode:
 2008ApJ...680...17W
 Keywords:

 cosmic microwave background;
 cosmological parameters;
 galaxies: clusters: general;
 hydrodynamics;
 intergalactic medium;
 largescale structure of universe;
 Astrophysics
 EPrint:
 16 pages, 6 figures, Accepted for publication in the Astrophysical Journal