Free Access
Issue
A&A
Volume 575, March 2015
Article Number A45
Number of page(s) 18
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/201423972
Published online 19 February 2015

Online material

Appendix A: Derivation of the flux densities of discrete sources

Here we report the details of the derivation of the discrete sources flux densities. All the values are listed in Table 3. The sources position in brackets are expressed in the J2000 coordinate system.

Source C tail (17 03 28, +78 39 57)

The peak of the emission of source C coincides with an optical galaxy with magnitude 15.3 (Bridle et al. 1979). The head-tail morphology for source C was first suggested by Bridle & Fomalont (1976). We modeled the source distinguishing between the head (long 756) and the tail as we are interested only on the contribution from the latter. At the highest frequency (10 450 MHz) the head of the source is still clearly visible, while it’s difficult to establish if the flux in the tail region is from the tail or from the underlying relic. The measured fluxes are S(head)10 450 = 2.1 ± 0.6 mJy and S(tail)10 450 = 1.9 ± 0.7 mJy and consequently S(all)10 450 = 4.0 ± 0.0; the last two can be considered as upper limits. Combining this values with the fluxes we measured at 2273 MHz (S(all)2273 = 33.7 ± 1.8 mJy; S(head)2273 = 17.3 ± 0.9 mJy; S(tail)2273 = 16.4 ± 0.9 mJy), we obtain spectral indeces , and . We used these values of the spectral indeces to extrapolate the fluxes of the components at 2640 and 4850 MHz. Lin et al. (2009) report a measured flux for the source C (referred to in the paper as 1706+787) of 5.06 ± 0.60 mJy at 4.9 GHz, classifying the source as a point source. Due to the wrong classification, we believe that their observations resolve out the tail of the source and the reported flux refers to the source head only. Indeed, their reported flux is in agreement with the flux that we extrapolated for the head of the source (S(head)4850 = 6.0 ± 0.9 mJy).

Rottgering et al. (1994) report a flux for the entire source at 327 MHz of 246 ± 20 mJy; combining this with our measurements at 1369 MHz (S(all)1369 = 56.5 ± 3.4) we find that the spectral index for the entire source keeps the same slope as in the range 13692273 MHz, . To separate the emission between the head and the tail we used the spectral index profile along the tail of the source C between 327 and 1447 MHz published by Rottgering et al. (1994, Fig. 7 right side). From the plot we deduced that the averaged spectral index of the head (selecting the range 0− ~ 75′′ in the x axes) is . From this we got a flux at 327 MHz for the head of 63.4 mJy and consequently a flux for the tail of S(tail)327 = 246.0−63.4 = 182.6 and a spectral index . We used this spectral index to calculate the fluxes at 351 MHz.

At 153 MHz van Weeren et al. (2012) report a flux for the enire source C of S(all)153 = 480 ± 50 mJy. The resulting spectral index is . From Fig. 5.4 (right panel) of Intema (2009) we deduce a value for the spectral index between 153 and 325 MHz for the head of the source of . We used this value to calculate the flux of the head S(head)153 = 92.7 ± 10.7 mJy. Consequently the tail has S(tail)153 = 387.3 ± 51.1 mJy and . We estrapolated the fluxes to 63 keeping costant the spectral indeces of the entire source and of the head. For the tail we obtain S(tail)63 = 903.5 ± 257.0 mJy.

Source K (17 02 18.4, +78 46 03.30)

Source K was first identified by Bridle et al. (1979) and can be associated with a star-forming galaxy (Miller et al. 2003).

Rottgering et al. (1994) report a flux for the source of 7.0 ± 1.0 mJy at 327 MHz and a flux of 3.4 ± 0.3 mJy at 1446 MHz. The latter is in agreement within the error bars with what we measured at 1369 MHz (3.3 ± 0.2 mJy). Combining these values with what we find at 2273 MHz (1.9 ± 0.2 mJy) we obtain a spectral index with a steepening at high frequency . We extrapolated the fluxes at 63 MHz and 351 MHz using and the fluxes at 2640 and 4850 MHz using . The contribution of the source to the total flux at 10 450 MHz is negligible (≪ 1 mJy).

Source J (17 01 12, +78 43 27)

Source J was first identified by Bridle et al. (1979). Measuring the fluxes at 1369 and 2273 MHz, we found that the source has an inverted-spectrum, in agreement with what reported by Rottgering et al. (1994). The source is indeed not visible at the 327 MHz (Rottgering et al. (1994) report an upper limit of 1 mJy), but become visible at 1369 MHz and its flux increase at 2273 MHz. At 10 450 MHz the source is again at a level <1 mJy. Fitting our measurements with the flux reported by Rottgering et al. (1994) at 327 and 1447 MHz, we find a spectral index and . We used this value to extrapolate the fluxes at 2640, 4850 and 10 450 MHz.

Source I (17 00 52.68, +78 41 23)

Source I is a head tail source first identified by Bridle et al. (1979). The flux we measured at 1369 MHz (9.3 ± 0.8) is in agreement with what reported in the literature at close frequencies (S1447 = 8.2 ± 1.8 mJy from Rottgering et al. (1994); S1400 = 10 mJy from Owen & Ledlow (1997), included in the fit). At 2273 MHz we measure a flux of 6.8 ± 0.4 mJy that imply a spectral index . At higher frequencies the source has been observed with the VLA by Lin et al. (2009) (and classified as extended source). They report S4900 = 2.14 ± 0.45 mJy and S8500 = 1.25 ± 0.36 mJy. Fitting these values with our measurement at 2273 MHz we find a spectral index that we used to extrapolate the fluxes at 2640, 4850 and 10 450 MHz. At 327 MHz Rottgering et al. (1994) report a flux of 8 ±1 mJy that would imply an inverted spectrum. However in their published map only the head is clearly visible, while the tail is resolved out. We treated their reported flux as a lower limit and we averaged it with the flux resulting from the extrapolation with the spectral index found (25.9 mJy), that represents, on the other hand, an upper limit. The resulting averaged flux is S327 = 17.0 ± 8.9 and consequently mJy. We used this value to estrapolate the fluxes at 63 and 351 MHz.

Source I2 (17 01 24, +78 41 13)

We measure, for source I2, a flux of 1.00 ± 0.07 mJy at 1369 MHz and 1.9 ± 0.1 mJy at 2273 MHz implying an inverted spectrum. The source is indeed invisible in the 327 MHz VLA map published by Rottgering et al. (1994). At 10 450 MHz we measure an upper limit <1 mJy.

Sources K2 (17 02 30, +78 45 00), J2 (17 00 51, +78, 42, 28), I3 (17 02 02, +78 40 32), G2 (17 03 22.7, +78 46 56.1)

For these sources only our measurements at 1369 MHz and 2273 MHz are available. We extrapolated the fluxes at the other frequencies assuming straight spectra.


© ESO, 2015

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