The project and its background

Observational astronomy has dramatically evolved over the last few decades as a result of the opening up of new observing windows in the electromagnetic spectrum and the development of efficient and large area detectors. Ground-based and space-borne all-sky surveys have provided an essential astrometric and photometric reference frame and the first true maps of the entire sky.

This ever-increasing wealth of multi-wavelength data has fundamentally changed the way astronomers now tackle scientific problems. The previous paradigm, typically focusing on a single wavelength range, has now evolved towards a systematic fully multi-wavelength approach. In fact, our understanding of the physics of stars and galaxies now essentially rests on the modelling of their electromagnetic spectra over the widest range of frequencies, spanning radio to the highest energy gamma-rays.

Despite the paramount scientific importance of large-scale multi-wavelength observational studies, obstacles still remain for their efficient utilisation by a large majority of astronomers.

The high-energy window to the Universe has strongly benefited from the recent availability of the European Space Agency (ESA) XMM-Newton space observatory. This large X-ray telescope routinely observes the sky with an image quality approaching that of ground-based optical telescopes, generating one of the key ESA astrophysical databases, the XMM-Newton X-ray catalogue, now extending to a half million entries.

New tools will be developed for cross-correlation with extensive archival resources, producing well-characterised multi-wavelength data in the form of spectral energy distributions for large sets of objects. We plan to create high reliability source crossidentifications extracted from the best archival astronomical catalogues so as to cover the widest range in wavelength. These cross-matches will then be used to build fully calibrated spectral energy distributions (SEDs). Most importantly, we will validate the quality of these products by using them in the framework of a small number of pilot projects tackling forefront astrophysical topics, providing the route for further enhancement.

ARCHES will considerably increase the usability and research potential of the XMM-Newton X-ray catalogue, enhancing it with key multi-wavelength resources and distributing these results to the international community.