SBCS+Rationale

=Santa Barbara Cluster Standards Project: Rationale=

Large scale cluster surveys during the coming decade are expected to deliver unprecedented numbers of clusters. With that statistical power comes the opportunity for much more accurate determination of cosmological parameters. However, even analyses using current cluster samples are limited primarily by systematic rather than statistical uncertainties. Expressing relationships between cluster masses and the observable properties that can be used as mass proxies is a key modeling element that the recent KITP meeting "Galaxy Clusters: the Crossroads of Cosmology and Astrophysics" exposed as ripe for improvement.

As discussed at KITP, the community would greatly benefit from adhering to a common set of defining conventions for quantifying halo masses and the observational mass proxies of clusters. While some de facto standards exist (e.g., M_500c), so do many variants. Most importantly, there is no organizational mechanism, other than scattered treatments in the literature, that clearly defines the possible conventions and argues their values in absolute and relative terms. Having such a clearly defined set of standard cluster quantities will facilitate progress on three fronts: improved observational calibrations of the mass proxies, greater accuracy in cosmological simulations of clusters, and fitting of parametric models to the results of large-scale surveys (i.e. self-calibration).

Therefore, to prepare for the coming era of large cluster databases, we need to develop a data model for clusters that will encourage interoperability, both across wavelength regimes as well as between the worlds of observation and simulation. In order to build on the momentum generated at the KITP workshop, we are encouraging the cluster community to participate in a wiki discussion that will serve as a platform for developing a publication on cluster standards.

This wiki site will host standard conventions for defining halo masses and galaxy cluster mass proxies. Recognizing that standard conventions will be more widely adopted if they are collectively developed, we are recommending the following format for the discussion:


 * Anyone may propose a standard quantity.
 * A proposed standard quantity must include a suggestion for standard notation (e.g., M_200c for mass within a sphere of mean density 200 times the critical density) and an algorithmic description of how one would measure that quantity.
 * Below the description of each standard quantity is a discussion of its strengths and weaknesses, to which anyone can contribute.
 * Links to software that can be used to measure the standard quantity are welcomed and will be greatly appreciated by the community.

Once the wiki definitions have stabilized, we intend to publish them in a journal article, listing everyone who made a significant contribution as an author, unless you choose to opt out.