Institute of Astronomy

Second Catalogue of Planck compact sources released

Published on 09/07/2015 

Figure caption: Map of selection of compact sources from the Second Planck Catalogue of Compact Sources. Credit: ESA and the Planck Collaboration

ESA's Planck mission is the source for a new catalogue, eagerly awaited by the scientific community, and available online from today. The Second Planck Catalogue of Compact Sources uses data from the entire mission to identify tens of thousands of compact sources, as well as providing polarisation data for several hundred of them. The new catalogue surpasses its predecessors not only in the quantity of sources but also in the quality of data. It will be an asset to astronomers working in a wide range of fields.

ESA's Planck telescope set out to measure tiny fluctuations in the Cosmic Microwave Background (CMB) – the thermal footprint left by the Big Bang. To achieve this, it continuously scanned the sky between 2009 and 2013, detecting the CMB as well as the foreground emissions arising from cosmic structures lying between the CMB and ourselves. The study of these foreground structures, which had to be carefully mapped and characterised in order to be separated from the CMB, has resulted in a valuable by-product: an extensive catalogue of tens of thousands of individual compact sources, released today. These sources appear to Planck as bright point-like spots superposed on wide expanses of more diffuse emission and consist mainly of galaxies located at great distances from the Milky Way, though compact objects within our Galaxy also appear in the catalogue.

 

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.

"There are a number of ways in which the data in this catalogue surpass those of its predecessors in more than just quantity," explains Marcos López-Caniego from ESA, responsible for the LFI portion of the survey. "For example, for the LFI channels, which cover the frequency range 30 to 70 GHz, averaging data over eight surveys has dramatically increased the sensitivity."

"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.

See the full ESA press release here

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Page last updated: 9 July 2015 at 16:16