Credit: ESA and the Planck Collaboration
ESA has released compact source catalogues from Planck in the past but in this instance the diverse and extensive catalogue includes data from the full Planck mission. The mission involved surveying the entire sky in nine different wavelengths spanning the far-infrared to radio, covering the spectral range 30 GHz to 857 GHz. The result is a catalogue with datasets from five surveys using the telescope's High Frequency Instrument (HFI) channels and a remarkable eight surveys using the Low Frequency Instrument (LFI) channels. This is a significant leap forward from the one and a half surveys used for the Early Release Compact Source Catalogue, released in 2011, and the 2.5 used in the 2013 catalogue that followed.
"Another major advance is in the better understanding of the contents of the catalogue," adds Diana Harrison from the Institute of Astronomy, University of Cambridge, UK, who was responsible for the HFI section of the catalogue. "One of the major complications at the wavelengths that Planck observes is to distinguish truly compact individual sources from variations in the diffuse emission which arises from gas and dust in our own Galaxy. In this catalogue there has been a totally new treatment of the reliability of the sources, especially in the HFI channels, which has resulted in much higher confidence in its contents."
The improvements to the reliability and sensitivity of the data are just part of the reason that this extensive database differs from those that came before. Planck has polarisation sensitive instruments in seven of the nine frequencies it observes in and this catalogue, unlike its predecessors, offers polarisation data for several hundred compact sources.
"For those sources that have been significantly detected in polarisation maps we have used the latest calibration of Planck data, and improved pipelines, to measure the polarised flux densities of the sources," explains Marcos. "In other words, we have measured and included the amount of polarised light we have collected radiating from these sources, which means that they can be studied in both total intensity and polarised light."
Catalogue use and applications
Researchers from across astronomy – including optical, infrared, radio, X-ray and gamma ray astronomers – will benefit from the catalogue, which can be used to build spectral energy distribution plots of individual objects or whole classes of objects. In other words, plotting the brightness of objects, over a range of frequencies, giving valuable clues to their properties. For others, a key benefit of the catalogue will be the ability to combine its full mission maps and single survey maps with the new tools in the Planck Legacy Archive to produce maps from specific periods of time. This will allow for long-term and short-term studies of how the objects vary over time.
Institute of Astronomy, University of Cambridge, UK
Tel: +44 1223 766 660
ESA European Space Astronomy Centre (ESAC), Madrid, Spainv
Tel: +34 91 813 1481
ESA Planck Project Scientist
Scientific Support Office
Directorate of Science and Robotic Exploration
ESA, The Netherlands
Tel: +31 71 565 5342