Volume 547, November 2012
|Number of page(s)||14|
|Section||Cosmology (including clusters of galaxies)|
|Published online||30 October 2012|
The strongest gravitational lenses
II. Is the large Einstein radius of MACS J0717.5+3745 in conflict with ΛCDM?
1 Dipartimento di AstronomiaUniversità di Bologna, via Ranzani 1, 40127 Bologna, Italy
2 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
4 Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
Received: 3 July 2012
Accepted: 7 August 2012
Context. With the amount and quality of galaxy cluster data increasing, the question arises whether or not the standard cosmological model can be questioned on the basis of a single observed extreme galaxy cluster. Usually, the word extreme refers directly to cluster mass, which is not a direct observable and thus subject to substantial uncertainty. Hence, it is desirable to extend studies of extreme clusters to direct observables, such as the Einstein radius.
Aims. We aim to evaluate the occurrence probability of the large observed Einstein radius of MACS J0717.5+3745 within the standard ΛCDM cosmology. In particular, we want to model the distribution function of the single largest Einstein radius in a given cosmological volume and to study which underlying assumptions and effects have the strongest impact on the results.
Methods. We obtain this distribution by a Monte Carlo approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the distribution, we fit the results with the general extreme value (GEV) distribution which we use for the subsequent analysis.
Results. We find that the distribution of the maximum Einstein radius is particularly sensitive to the precise choice of the halo mass function, lens triaxiality, the inner slope of the halo density profile and the mass-concentration relation. Using the distributions so obtained, we study the occurrence probability of the large Einstein radius of MACS J0717.5+3745, finding that this system is not in tension with ΛCDM. We also find that the GEV distribution can be used to fit very accurately the sampled distributions and that all of them can be described by a (type-II) Fréchet distribution.
Conclusions. With a multitude of effects that strongly influence the distribution of the single largest Einstein radius, it is more than doubtful that the standard ΛCDM cosmology can be ruled out on the basis of a single observation. If, despite the large uncertainties in the underlying assumptions, one wanted to do so, a much larger Einstein radius (≳100″) than that of MACS J0717.5+3745 would have to be observed.
Key words: gravitational lensing: strong / methods: statistical / galaxies: clusters: general / cosmology: miscellaneous / galaxies: clusters: individual: MACS J0717.5+3745
© ESO, 2012
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.