Free Access
Volume 506, Number 3, November II 2009
Page(s) 1083 - 1094
Section Cosmology (including clusters of galaxies)
DOI https://doi.org/10.1051/0004-6361/200912287
Published online 27 August 2009

Online Material

Appendix A: Compact sources at 610 MHz and optical counterparts

To identify optical counterparts for the radio sources we have overlaid the 610 MHz radio contours on SDSS images, see Figs. A.1, A.2, and A.3.

Source A is resolved, 13 $^{\prime \prime }$ by 19 $^{\prime \prime }$, with the brightest part of the emission located to the southeast. The resolution is insufficient to classify the source, but the morphology is consistent with a head-tail source. A spectral index gradient is also observed towards the northwest (Sect. 5.1). An optical counterpart is visible to the southwest of the center of the radio source, close to the peak of the radio emission (see Fig. A.1). The photometric redshift ( $z_{{\rm phot}}$) of this galaxy is 0.32, consistent with being a cluster member. The E/S0 galaxy (mag $_{{\rm r}}$= 18.65) has a close companion (mag $_{{\rm r}}$= 21.12) about 3 $^{\prime \prime }$ to the southwest. The spectral index of A is -0.92, between 157 and 1400 MHz, typical for a radio galaxy. The source therefore does not seem to be directly related to the diffuse emission within the cluster, as suggested by Bagchi et al. (2002).

Source B has a peculiar morphology, resembling a head-tail galaxy. A mag $_{{\rm r}}$= 18.65 E/S0 counterpart is located at $z_{{\rm phot}} =0.29$. The direction of the tail suggest the galaxy is falling in from the north towards the cluster center. The spectral index of the source is -0.76 (between 241 and 610 MHz). Other sources north of the cluster center are sources C, E, and F. Source C has a blue star-forming galaxy (mag $_{{\rm r}} = 17.87$) as an optical counterpart at z=0.261 (spectroscopic redshift). The SDSS DR6 spectrum of this galaxy shows strong emission lines (in particular H$\alpha$). A close companion is located about 4 $^{\prime \prime }$ to the west. The E/S0 mag $_{{\rm r}}$= 18.06 counterpart of source F has a spectroscopic redshift of 0.269, and the SDSS spectrum shows a strong Balmer break. The mag $_{{\rm r}}$= 20.11 optical counterpart of E is located at $z_{{\rm phot}} =0.45$ and may therefore not be associated with the cluster.

To the south of the cluster center we have sources G, H, I, J, K, and L. Source G is probably a head-tail source, with the tail pointing south, indicating the galaxy is also falling towards the cluster center. The spectral index $\alpha_{241}^{610}$ of -1.53 is consistent with such an identification, and there is a hint of spectral steepening towards the south. The counterpart of source G is an E/S0 mag $_{{\rm r}}$= 18.35 galaxy (located at $z_{{\rm phot}} =0.35$) with two close companions. The counterpart of source H is a blue mag $_{{\rm r}}$= 18.02 galaxy at $z_{{\rm phot}} =0.28$. The spectral index $\alpha_{241}^{610}$ of $\sim $-1.08, quite steep for a star-forming galaxy (e.g., Thompson et al. 2006; Bondi et al. 2007; Windhorst et al. 1993), this indicates that an AGN may also be present. The counterpart of source I is an E/S0 mag $_{{\rm r}} = 18.45$galaxy located at $z_{{\rm phot}} =0.26$. The counterpart of source L is an E/S0 mag $_{{\rm r}}$= 19.84 galaxy with $z_{{\rm phot}} =0.30$ and $\alpha_{241}^{610} \sim -0.5$. The galaxy is located roughly in the middle between RS-1 and RS-2. Radio sources J and K are diffuse with sizes of about 10 $^{\prime \prime }$. Source K has no counterpart, while source J has a possible mag $_{\rm r}= 22.23$, $z_{{\rm phot}} =0.18$counterpart. However, J and K could also be the two lobes of a distant radio galaxy.

\end{figure} Figure A.1:

SDSS DR7 image color image (g, r, and i bands) of the cluster center overlaid with radio contours. The 610 MHz contour levels are drawn at $\sqrt {[1, 8, 32, 128, ...]} \times 84$ $\mu $Jy beam-1. The beam size of $6.9\hbox {$^{\prime \prime }$ }\times 4.3\hbox {$^{\prime \prime }$ }$ is indicated in the bottom left corner.

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\end{figure} Figure A.2:

SDSS DR7 image color image (g, r, and i bands) of the northern part of the cluster overlaid with 610 MHz radio contours. Contours are drawn at the same levels as in Fig. A.1.

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\par\includegraphics[angle=90,width=16cm,clip]{12287f10} %\end{figure} Figure A.3:

SDSS DR7 image color image (g, r, and i bands) of the southern part of the cluster overlaid with 610 MHz radio contours. Contours are drawn at the same levels as in Fig. A.1.

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