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Description
The Planck mission, thanks to its large frequency range and all-sky coverage, has a unique potential for systematically detecting the brightest, and rarest, sub-millimeter sources on the sky, including distant objects in the high-redshift Universe traced by their dust emission. A novel method, based on a component-separation procedure using a combination of Planck and IRAS data, has been validated and characterized on numerous simulations, and applied to select the most luminous cold sub-millimeter sources with spectral energy distributions peaking between 353 and 857GHz at 5-arcminute resolution. A total of 2,151 Planck high-z source candidates (the PHZ list) have been detected in the cleanest 26% of the sky, with flux density at 545 GHz above 500 mJy. Embedded in the cosmic infrared background close to the confusion limit, these high-z candidates exhibit colder colors than their surroundings, consistent with redshifts z greater than 2, assuming a dust temperature of T<sub>xgal</sub> = 35 K and a spectral index of beta<sub>xgal</sub> = 1.5. Exhibiting extremely high luminosities, larger than 10<sup>14</sup> L<sub>sun</sub>, the PHZ objects may be made of multiple galaxies or clumps at high redshift, as suggested by a first statistical analysis based on a comparison with number count models. Furthermore, first follow-up observations obtained from optical to sub-millimeter wavelengths, which can be found in companion papers, have confirmed that this list consists of two distinct populations. A small fraction (around 3%) of the sources have been identified as strongly gravitationally lensed star-forming galaxies at redshift 2 to 4, while the vast majority of the PHZ sources appear as overdensities of dusty star-forming galaxies, having colors consistent with being at z > 2, and may be considered as proto-cluster candidates. The PHZ provides an original sample, which is complementary to the Planck Sunyaev-Zeldovich Catalog (PSZ2); by extending the population of virialized massive galaxy clusters detected below z < 1.5 through their SZ signal to a population of sources at z > 1.5, the PHZ may contain the progenitors of today's clusters. Hence the Planck list of high-redshift source candidates opens a new window on the study of the early stages of structure formation, particularly understanding the intensively star-forming phase at high-z. The compact source detection algorithm used herein requires positive detections simultaneously within a 5-arcminute radius in the 545-GHz excess map, and the 857-, 545-, and 353-GHz cleaned maps. It also requires a non-detection in the 100-GHz cleaned maps, which traces emission from synchrotron sources. A detection is then defined as a local maximum of the signal-to-noise ratio (S/N) above a given threshold in each map, with a spatial separation of at least 5 arcminutes being required between two local maxima. A threshold of S/N > 5 is adopted for detections in the 545-GHz excess map, while this is slightly relaxed to S/N > 3 for detections in the cleaned maps because the constraint imposed by the spatial consistency between detections in all three bands is expected to reinforce the robustness of a simultaneous detection. Concerning the 100-GHz band, the authors adopt a similar threshold by requiring the absence of any local maximum with S/N > 3 within a radius of 5 arcminutes. The HEASARC has changed the names of many of the parameters from those given in the original table. In such cases we have listed the original names in parentheses at the end of the parameter descriptions given below. This table was created by the HEASARC in May 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/596/A100">CDS Catalog J/A+A/596/A100</a> file phz.dat. This is a service provided by NASA HEASARC .
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