Saturday, 17 November 2012
First Light for the Millennium Run Observatory
In analogy to the moment when newly constructed astronomical observatories receive their “first light”, the Millennium Run Observatory (MRObs) has produced its first images of the simulated universe. These virtual observations allow theorists and observers to analyse the purely theoretical data in exactly the same way as they would purely observational data. Building on the success of the Millennium Run Database, the simulated observations are now being made available to the wider astronomical community for further study. The MRObs browser - a new online tool - allows users to explore the simulated images and interact with the underlying physical universe as stored in the database. The team expects that the advantages offered by this approach will lead to a richer collaboration between theoretical and observational astronomers.
Cosmological simulations aim to capture our current understanding of galaxy evolution, aid in the interpretation of complex astronomical observations, and make detailed predictions for future experiments. Simulations and observations, however, are often compared in a somewhat indirect way: physical quantities are estimated from the observational data and compared to the models. An important complication with this approach is that observations typically give a highly distorted view of the universe, making the process of extracting physical information a challenge.
Many problems in astrophysics could therefore benefit from doing it the other way round: the entire observing process is applied to the simulations, so that the models can be viewed fully from an observer’s perspective. A small team composed of current and former members of the Max Planck Institute for Astrophysics has now developed the Millennium Run Observatory (MRObs), a theoretical, virtual observatory that uses virtual telescopes to ‘observe’ semi-analytic galaxy distributions based on the MR dark matter simulations developed at MPA. The MRObs produces data that can be processed and analysed using standard observational software packages developed for real observations.
The MRObs extends the MR simulations by producing data products that most directly correspond to observations, namely synthetic images and extracted source catalogues. The data simulated with the MRObs so far includes portions of the Sloan Digital Sky Survey (SDSS), the Canada France Hawaii Telescope Legacy Survey (CFHT-LS), the Great Observatories Origins Deep Survey (GOODS), the GOODS WFC3 Early Release Science (ERS), the Hubble Ultra Deep Field (HUDF, see Figure 1), as well as the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The information provided covers light cone catalogues linked to structural properties of galaxies, pre-observation model images, mock telescope images and source catalogues that can all be traced back to the dark matter, semi-analytic galaxy and light cone catalogues already available in the MR database. This will aid theorists in testing analytical models against observations, aid observers in making detailed predictions for observations as well as better analyses of observational data, and allow the community to subject the models to new tests. For example, the MRObs can be used to visualize the appearance of galaxy clusters, to predict the structural properties of galaxies across the stellar mass versus star formation rate plane (see Figure 2), or to answer the question of how many galaxies could be detected at a redshift of about 10. The data can be explored interactively in the MRObs browser (Figure 3).
The development of the MRObs coincides with the celebration of the first 500 papers based on the MR simulations, proving that the MPA-led Millennium Run project is still as successful today as it was 7 years ago. Future expansions of the MRObs project are already underway, such as incorporating the more recent Millennium-Run II and Millennium XXL simulations to extend the dynamic range, implementing improved cosmological parameters and galaxy modelling techniques, and creating a wider range of virtual telescopes and simulated surveys that will aid theorists and observers alike.