EDP Sciences
Free access
Volume 550, February 2013
Article Number A133
Number of page(s) 19
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361/201220053
Published online 07 February 2013

Online material

Appendix A: Spectral classification; effect of intermediate sources and photometric noise

In this appendix, we investigate the fate and influence of the so-called “intermediate” sources as defined in Sect. 3.

thumbnail Fig.A.1

As in Fig. 8, the fraction of source type (dusty, red squares; synch, blue triangles) as a function of frequency. The difference is that we have now included the “intermediate” population (green diamonds). We can see that at most 13% of our classification as dusty or synchrotron can be affected by intermediate sources. Our number counts by type (above 80% completeness) are thus almost unaffected by these intermediate type sources.

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Figure A.1 shows the fraction of sources (like Fig. 8) by type (dusty, synchrotron, and now intermediate) as a function of frequency computed for sources above 80% completeness. The fraction is at most 13%, and is on average around 7%. The intermediate source population thus has no impact on our number counts by type.

We conclude that a genuine population of intermediate sources exist (i.e. having both a thermal dust emission component and a synchrotron component) but its contribution in number is less than typically 10% (Fig. A.1). Notice that a free-free emission can also play a role in the spectrum flattening around 100 GHz (Peel et al. 2011).

We notice, however, that this intermediate populations lies at the faint end of the flux distribution (i.e. they usually are among the faintest sources of our sample). To investigate further if the presence of intermediate sources is linked to the level of photometric noise, we performed the classification on our whole sample, thus including sources at fluxes below the 80% completeness limit. The results, shown in Fig. A.2, indicates that the higher the photometric noise the more sources are classified as intermediate.

When using the total sample (i.e. with sources fainter that the 80% completeness cut), the fraction of intermediate sources increases, but those sources are always at the faint end of the flux distribution: the effect of the photometric noise is thus mainly responsible for the uncertain classification. This emphasises that we should use highly-complete samples for such statistical analysis, in order not to be biased towards mis-classification.

thumbnail Fig.A.2

Like Fig. A.1, the fraction of source type (dusty, red squares; synchrotron, blue triangles; green diamonds, intermediate) as a function of frequency. The difference is that we have now included the whole catalogue, i.e. including sources affected by more photometric noise below the 80% completeness limit cut. The effect of increasing noise is to induce more sources to be classified as intermediate.

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Appendix B: Some peculiarities; individual sources or groups of sources

thumbnail Fig.C.1

Planck differential number counts (total, dusty and synchrotron) at 6 frequencies between 100 and 857 GHz, normalized to the Euclidean, for each zone (filled circles): deep (red), medium (green) and shallow (blue). Diamonds are from Planck HFI (Planck Collaboration 2011d), triangles from Herschel SPIRE (Oliver et al. 2010; Clements et al. 2010) and BLAST Bethermin et al. (2010b). The bump at 4 Jy at 545 GHz (and at 10 Jy at 857 GHz) in the medium zone is discussed in Sect. B.3.

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While the SEDs of some particular sources have been published in the Planck early papers Planck Collaboration (2011e–g), we review here some specific sources detected at low or high frequency, but with unexpected classifications.

B.1. Low-frequency dusty galaxies

There are seven low-frequency sources (three detected at 100 GHz and four at 143 GHz) that are classified as dusty galaxies. This kind of classification is not necessarily expected, unless we detect local galaxies showing both radio and infrared components. For this reason we check them individually.

  • 1)

    PLCKERC100 G062.69−14.07: there is no radio identificationin NVSS & GB6 or in NED, and no detection at LFI frequencies.This source is likely correctly classified as a dusty galaxy.

  • 2)

    PLCKERC100 G140.41−17.39: this source is found with NED to be NGC891. There is no LFI detection, but detections in NVSS/GB6. We might be seeing two spectral components (dusty and synchrotron) of this nearby galaxy.

  • 3)

    PLCKERC100 G141.42+40.57: this is NGC3034 (M82). As above we are sensitive to both components of this nearby and well-studied galaxy.

  • 4)

    PLCKERC143 G001.33−20.49: no LFI detection nor radio identification. this source is correctly classified as a dusty galaxy.

  • 5)

    PLCKERC143 G148.59+28.70: this source is likely a blazar with an almost flat spetrcum at high frequencies and detections in NVSS and GB6. This source is likely incorrectly classified as dusty, because of the small jump in flux at 545 GHz.

  • 6)

    PLCKERC143 G236.47−14.38: no LFI detection nor radio identification. This source is correctly classified as a dusty galaxy.

  • 7)

    PLCKERC143 G349.61−52.57: no LFI detection. At 0.2 to 20 GHz it is identified as a flat-spectrum source but its high-frequency spectrum shows a clear dusty behaviour. This source is correctly classified as a dusty galaxy, although a clear radio component is detected.

B.2. High frequency synchrotron galaxies

There are four sources classified at synchrotron sources at 857 GHz. We also check them individually.

  • 1)

    PLCKERC857 G206.80+35.82: this is a confirmed blazardetected with WMAP. This source is correctly classified assynchrotron-dominated.

  • 2)

    PLCKERC857 G237.75−48.48: this is a confirmed blazar detected with WMAP and ATCA. This source is correctly classified as synchrotron-dominated.

  • 3)

    PLCKERC857 G250.08−31.09: this is a confirmed blazar detected with WMAP and ATCA. This source is correctly classified as synchrotron-dominated.

  • 4)

    PLCKERC857 G148.24+52.44: this is NGC3408, quite faint for Planck at high frequencies (812mJy at 857 GHz and not detected at 545 GHz). This source, although in our sample defined in Sect. 2.3, was not used in the number counts because of the low completeness level at this flux density.

B.3. Bump at 4 Jy at 545 GHz in the medium zone

As discussed in Sect. 4 and shown in Fig. C.1, there is an excess of 545 GHz sources in the medium zone at 4 Jy, which is also seen at 857 GHz at 10 Jy and at 353 GHz at 1 Jy. This bump is created at 545 by 18 sources (between 3 and 5 Jy). Among the

sources, we find NGC3147, NGC4449, NGC4217, NGC3992, NGC4088, NGC4096, NGC4051, NGC3631, NGC3938, IC0750, NGC4244, NGC3726, NGC4214, NGC7582 and NGC7552. At 857 GHz, we find 20 sources between 7.6 and 12 Jy, with many in common with the list above. These sources are not physically associated and are spread over a large surface of the sky, although the majority lie around (150 deg, 60 deg) in Galactic coordinates.

Appendix C: Number counts by zone

Figure C.1 shows the number counts for each of the three zones: deep, medium, and shallow. This illustrates the sample variance, as mentioned in Appendix B.3.

Since, with the exception of one zone at 545 GHz, there is little difference between the counts in different zones, this figure also demonstrates that the weight given to each zone in calculating the total number counts has little influence on the result.

© ESO, 2013