Difference between revisions of "Compact Source catalogues"

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==Planck Catalogue of Compact Sources==
==Planck Catalogue of Compact Sources==
'''The Second Planck Catalogue of compact source will be available in the next release of the Planck 2015 results.'''
'''The Second Planck Catalogue of Compact Sources will be available in the next release of the Planck 2015 results.'''

Revision as of 21:46, 4 February 2015

Planck Catalogue of Compact Sources[edit]

The Second Planck Catalogue of Compact Sources will be available in the next release of the Planck 2015 results.

Planck Sunyaev-Zeldovich catalogue[edit]

The Planck SZ catalogue is a nearly full-sky list of SZ detections obtained from the Planck data. It is fully described in Planck-2013-XXIX[1], Planck-2015-A36[2]. The catalogue is derived from the HFI frequency channel maps after masking and filling the bright point sources (SNR >= 10) from the PCCS catalogues in those channels. Three detection pipelines were used to construct the catalogue, two implementations of the matched multi-filter (MMF) algorithm and PowellSnakes (PwS), a Bayesian algorithm. All three pipelines use a circularly symmetric pressure profile, the non-standard universal profile from [3], in the detection.

  • MMF1 and MMF3 are full-sky implementations of the MMF algorithm. The matched filter optimizes the cluster detection using a linear combination of maps, which requires an estimate of the statistics of the contamination. It uses spatial filtering to suppress both foregrounds and noise, making use of the prior knowledge of the cluster pressure profile and thermal SZ spectrum.
  • PwS differs from the MMF methods. It is a fast Bayesian multi-frequency detection algorithm designed to identify and characterize compact objects in a diffuse background. The detection process is based on a statistical model comparison test. Detections may be accepted or rejected based on a generalized likelihood ratio test or in full Bayesian mode. These two modes allow quantities measured by PwS to be consistently compared with those of the MMF algorithms.

A union catalogue is constructed from the detections by all three pipelines. A mask to remove Galactic dust, nearby galaxies and point sources (leaving 83.7% of the sky) is applied a posteriori to avoid detections in areas where foregrounds are likely to cause spurious detections.

Catalogue of Planck Galactic Cold Clumps[edit]

The catalogue of Planck Galactic Cold Clumps (PGCC) is a list of 13188 Galactic sources and 54 sources located in the Small and Large Magellanic Clouds, identified as cold sources in Planck data, as described in Planck-2015-A37[4]. The sources are extracted with the CoCoCoDeT algorithm (Montier, 2010), using Planck-HFI 857, 545, and 353 GHz maps and the 3 THz IRIS map (Miville 2005), an upgraded version of the IRAS data at 5 arcmin resolution. This is the first all-sky catalogue of Galactic cold sources obtained with homogeneous methods and data.

The CoCoCoDeT detection algorithm uses the 3 THz map as a spatial template of a warm background component. Local estimates of the average colour of the background are derived at 30 arcmin resolution around each pixel of the maps at 857, 545, and 353 GHz. Together these describe a local warm component that is subtracted, leaving 857, 545, and 353 GHz maps of the cold residual component map over the full sky. A point source detection algorithm is applied to these three maps. A detection requires S/N > 4 in pixels in all Planck bands and a minimum angular distance of 5 arcmin to other detections.

A 2D Gaussian fit provides an estimate of the position angle and FWHM size along the major and minor axes. The ellipse defined by the FWHM values is used in aperture photometry to derive the flux density estimates in all four bands. Based on the quality of the flux density estimates in all four bands, PGCC sources are divided into three categories of FLUX_QUALITY:

  • FLUX_QUALITY=1 : sources with flux density estimates at S/N > 1 in all bands ;
  • FLUX_QUALITY=2 : sources with flux density estimates at S/N > 1 only in 857, 545, and 353 GHz Planck bands, considered as very cold source candidates ;
  • FLUX_QUALITY=3 : sources without any reliable flux density estimates, listed as poor candidates.

We also raise a flag on the blending between sources which can be used to quantify the reliability of the aperture photometry processing.

To estimate possible contamination by extragalactic sources we (1) cross-correlated the positions with catalogues of extragalactic sources, (2) rejected detections with SED [in colour-colour plots] consistent with radio sources, and (3) rejected detections with clear association to extragalactic sources visible in DSS images. Compared to the original number of sources, these only resulted in a small number of rejections.

Distance estimates, combining seven different methods, have been obtained for 5574 sources with estimates ranging from hundreds of pc in local molecular clouds up to 10.5 kpc along the Galactic plane. The methods include cross-correlation with kinematic distances previously listed for infrared dark clouds (IRDCs), optical and near-infrared extinction using SDSS and 2MASS data, respectively, association with molecular clouds with known distances, and finally referencing parallel work done on a small sample of sources followed up with Herschel. Most PGCC sources appear to be located in the solar neighbourhood.

The derived physical properties of the PGCC sources are: temperature, column density, physical size, mass, density and luminosity. PGCC sources exhibit an average temperature of about 14K, and ranging from 5.8 to 20K. They span a large range of physical properties (such as column density, mass and density) covering a large varety of objects, from dense cold cores to large molecular clouds.

The validation of this catalogue has been performed with a Monte Carlo Quality Assessment analysis wich allowed us to quantify the statistical reliability of the flux densities and of the source position and geometry estimates. The position accuracy is better than 0.2' and 0.8' for 68% and 95% of the sources, respectively, while the ellipticity of the sources is recovered with an accuracy better than 10% at 1[math]\sigma[/math]. This kind of analysis is also very powerful to characterize the selection function of the CoCoCoDeT algorithm applied to Planck data. The completeness of the detection has been studied as a function of the temperature of the injected sources. It has been shown that sources with FLUX_QUALITY=2 are effectively sources with low temperatures and have a high completeness level for temperatures below 10K.

We computed the cross-correlation between the PGCC catalogue and the other internal Planck catalogues: PCCS2, PCCS2E, PSZ and PHz. The PGCC catalogue contains about 45% new sources, not simultaneously detected in the 857, 545, and 353 GHz bands of the PCCS2 and PCCS2E. A few sources (65) are also detected in the PSZ2 and PGCC catalogues, suggesting a dusty nature of these candidates. Finally there are only 15 sources in common between the PGCC and PHz (which is focused on extragalactic sources at high redshift), that require further analysis to elucidate.

The PGCC catalogue contains also 54 sources located in the Small and Large Magellanic Clouds (SMC and LMC), two nearby galaxies which are so close that we can identify individual clumps in them.



(Planck) High Frequency Instrument