ASTROPHYSICS

The outcome of a large set of cosmological, hydro-dynamical simulations from the project Magneticum now became made available to the general community through operating a cosmological simulation web portal. Users are able to access data products extracted from the simulations via a user-friendly web interface, browsing through visualizations of cosmological structures while guided by meta data queries helping to select galaxy clusters and galaxy groups of interest. Several services are available for the users: (I) ClusterInspect; (II) SimCut (raw data access); (III) Smac (2D maps); (IV) Phox (virtual X-ray observations, taking the specifications of various, existing and future X-ray telescopes into account.

Introduction

Within modern cosmology, the Big Bang marks the beginning of the universe and the creation of matter, space and time about 13.8 billion years ago. Since then, the visible structures of the cosmos have developed: billions of galaxies which bind gas, dust, stars and planets with gravity and host supermassive black holes in their centres. But how could these visible structures have formed from the Universe’s initial conditions?

To answer this question, theoretical astrophysicists carry out large, cosmological simulations. They transform our knowledge about the physical processes which drive the formation of our universe into models and simulate the resulting evolution of our universe across a large range of spacial scales and over billions of years. To be comparable to ongoing and future cosmological surveys, such theoretical models have to cover very large volumes, especially to host the rarest, most massive galaxy clusters expected to be the lighthouses of structure formation detectable already at early times (e.g. at high redshifts).

While the Universe makes its transition from dark matter dominated to dark energy dominated (i.e. accelerated expansion), the objects which form within it make their transition from young, dynamically active and star formation driven systems to more relaxed and equilibrated systems observed at late time (e.g. low redshifts). Especially here, theoretical models in form of complex, hydrodynamical cosmological simulations are needed to disentangle the internal evolution of clusters of galaxies with respect to the evolution of the cosmological background. Such simulations will be essential to interpret the outstanding discoveries expected from upcoming surveys.

To make the outcome of such large cosmological hydrodynamics simulations available to a broad scientific community, LRZ in cooperation with experts from C²PAP (the Excellence Cluster Universe's datacentre) has now opened access to the Cosmological Web Portal [1], which now has already more than 150 registered users (see figure 1 for a usage statistics). In a first step, two of the largest simulation sets form the Magneticum Pathfinder Project [2] where made public.

Challenges of the Web Portal

The Web portal is based on a multi-layer structure, see [3,4] for more details. Between those layers, data and processes flow over the web portal with its web interface, several databases, the backend within the job control layer, the compute cluster (where the analysis tools are actually executed) and the storage system (where the raw simulation data are stored). The need for a separation between the web interface and the backend arises from both the necessity of users to run personalized jobs on raw data, managed by a job scheduler of the compute cluster and the protection of the data from unauthorized access.

As compute layer, currently the C²PAP compute cluster, operated by the Excellence cluster Origin and Structure of the Universe [5] is used while for the HPC storage we make use of the new Data Science Storage service at LRZ. All other processes are virtualised using the LRZ machines. Almost all parts of the implementation is based on common packages and publicly available libraries, except the core of the backend, which is a customized component tailored for the data flows, job requests and specific needs of the used scientific data analysis software. All services are based on standard post-processing tools as used in scientific analysis of such simulations.

The Web Interface

The visual frontend allows to explore the cosmological structures within the simulation, based on panning through and zooming into high resolution, 256 megapixel size images which are available for numerous outputs of the different simulations. A special layer-spy option can be used to show a second, smaller, visualization within a lens which can be moved freely over the whole image and moving the layer spy over the visible objects reveals immediately and intuitively the connection between the different components.