6 FIRBACKsource catalogs

6.1 ISO FIRBACKsource catalog

The final catalog, the ISO FIRBACKSource Catalog (IFSC), contains 106 sources with fluxes between 180 mJy ($4 \sigma$) and 2.4 Jy. The catalog is given for each field in Tables 7 to 10. All the sources have been checked for detection in all individual measurements. It is interesting to note that above $5 \sigma_{\rm c}$ the source density is constant in the fields, with 16 sources in FSM, 15 in FN2, and 32 sources in FN1 which is twice the size of the other fields. The source density is thus $16 \pm 4$ sources brighter than 225 mJy per square degree. At the $4 \sigma _{\rm c}$ limit, the source density is $27 \pm 5$sources brighter than 180 mJy per square degree, with a larger field-to-field dispersion. The brightest sources in FSM lie at 497 and 443 mJy, in FN1 at 838, 597 and 545 mJy, and in FN2 at 2377, 1251, 803, 682, 666 and 522 mJy.

Figure 12: Completeness of the FIRBACK catalog, computed from the simulations as the ratio of the number of detected sources to the number of added sources.

Figure 13: Malmquist-Eddington bias. Ratio of simulated source counts to simulated observed source counts. Due to flux uncertainties, the number of counts is overestimated at low flux levels.

6.2 Complementary ISO FIRBACKsource catalog

Sources with flux levels above the $3 \sigma_{\rm c}$ limit are higher redshift candidates and they can be used for statistical study of the nature of 170 $\mu$m sources. Nevertheless, the lower signal to confusion-noise ratio leads to lower flux accuracy - reduced to about 25% at 135 mJy - and may include spurious sources: this larger uncertainty suggests avoiding the use of these sources, e.g. in the counts.

Candidates for z > 1 may be selected on the basis of photometric redshift using the FIR-radio correlation (Condon 1992; Helou et al. 1985) and the submillimetre-radio correlation (Carilli & Yun 2000). The success of recent submillimetre detections of FIRBACKsources with SCUBA at the JCMT (Scott et al. 2000, with an rms sensitivity of 2 mJy), and with MAMBO at IRAM-30 m (with an rms sensitivity better than 0.5 mJy, Lagache et al., in prep.) in the millimetre range confirms the relevance of this technique.

   

Table 4: Number of sources per flux bin in $3.89^{\circ \, 2}$ used for the source counts, without any correction.

flux min	flux max	number per	cumulative
(mJy)	(mJy)	bin	number
180.0	190.0	13	106
190.0	210.0	20	93
210.0	240.0	21	73
240.0	300.0	24	52
300.0	500.0	19	28
500.0	$\infty$	9	9

In this frame of mind, we compile a Complementary ISO FIRBACKSource Catalog (CIFSC, Tables 11 to 13 for each field) which contains 90 sources whose flux levels lie in the range 135 to 180 mJy (3 to $4 \sigma _{\rm c}$). All the sources have been checked for detection in all individual measurements. There are 15 sources in FSM, 47 in FN1, and 28 in FN2. As an example, Fig. 9 shows of the detected sources in the FN1 field. At this flux level, the source density is not constant between the fields and fluctuates at about $23 \pm 8$ sources per square degree in the range 135-180 mJy.