Conclusions, Tables and Figures

We have found that the COSMOS/UKST Southern Sky Object Catalogue is a valuable resource for making optical identifications of MOST radio sources. Tentative identifications can be made quickly and efficiently for unresolved and slightly resolved sources, but users need to be aware of occasional object misclassifications. Visual inspection is the only practical way to identify complex extended sources, especially nearby cluster sources with highly distorted morphologies. Overlays of radio images on the DSS provide the most convenient method for assessing the reliability of such associations. In a first attempt to separate cluster radio galaxies from interlopers, we find a concentration strongly peaked towards the centres of the clusters, together with a lesser concentration extending out to 500 kpc.

Table 1: The sample of clusters studied in this paper.

Cluster	RA	Dec	Abell	B-M	R	D		z	rms (full)	rms (inner)
	(J2000)	(J2000)	Type	Type					(mJy/beam)	(mJy/beam)
A2731	00 10 12	-56 59	I	III	0	3	15.3	0.0312	1.28	0.99
S52	00 27 42	-54 11	IR	II	0	5	17.2	0.104	1.13	1.10
A2806	00 40 12	-56 09	RI	I-II	0	3	15.3	0.0271	1.13	0.91
A3125	03 27 24	-53 30	I	III	0	4	15.8	0.0593	2.13	1.66
A3128	03 30 12	-52 33	RI	I-II	3	3	15.3	0.0554	1.14	1.01
A3144	03 37 06	-55 01	IR	I-II	1	4	15.8	0.0423	1.21	0.88
A3164	03 45 48	-57 02	IR:	I-II	0	4	15.7	0.0611	1.21	0.95
A3202	04 00 12	-53 39	I	II	1	4	15.8	0.0338	1.29	0.86
S463	04 29 12	-53 49	R:	I-II	0	3	15.3	0.0394	2.13	2.69
S522	05 18 24	-56 13	RI	I-II	0	5	16.9	0.092	1.50	1.82
A3391	06 26 18	-53 40	R	I	0	4	16.1	0.0531	1.78	3.47
A3395	06 27 30	-54 23	R	II	1	4	15.9	0.0498	2.84	2.49
A3651	19 52 12	-55 05	RI:	II	1	3	15.4	0.0588	1.72	1.52
S839	20 01 18	-52 55	IR	I-II:	0	3	15.4	0.0526	1.58	1.93
S840	20 03 24	-55 57	RI:	I-II:	0	1	13.9	0.0152	0.76	1.25
S854	20 11 24	-56 44	IR	II	0	4	15.7	0.0536	1.54	1.61
A3667	20 12 30	-56 48	IR:	I-II	2	3	15.4	0.0552	1.18	1.39
A3716	20 51 30	-52 42	IR	I-II:	1	3	15.0	0.0456	1.79	1.50
A3785	21 34 30	-53 37	I	II	0	4	16.2	0.0775	1.44	1.66
A3806	21 46 36	-57 17	R	II	2	4	16.2	0.0747	1.07	0.92
A3816	21 50 24	-55 18	I	I-II	0	3	15.3	0.0352	1.44	1.29
A3826	21 59 54	-56 09	I	II	1	3	15.1	0.0754	1.35	1.18
A3851	22 16 42	-52 35	I	I-II	0	4	16.0	0.0529	1.21	1.13
A3869	22 21 24	-55 07	I	II:	0	3	15.3	0.0396	1.22	0.95
A3886	22 31 42	-54 44	I	III	0	4	17.3	0.0750	1.22	1.06
S1039	22 34 54	-52 27	I	I-II:	0	4	16.4	0.0554	1.44	1.45
A3911	22 46 06	-52 43	RI:	II-III	1	5	17.1	0.100	1.09	0.94
S1115	23 22 00	-54 46	R	III	0	6	17.6	0.123	1.78	1.93

Not in sample (see text)

From Sodré et al. (1992)

Table 2: Optical identifications for 927 radio sources in 27 cluster fields

Object type	Number of Identifications	Percentage of Identifications
Galaxies	191	21 1.5
Possible QSOs	43	4.6 0.7

 
Figure 1: Differences in RA (top) and Dec (bottom) between pairs of observations of identical sources (after subtraction of systematic offsets and removal of obvious outliers), as a function of peak flux density. The variances in RA and Dec differences were fitted to equation 1 to define the noise component of position uncertainties.

 
Figure 2: Probability that the closest object to a radio position is a chance association, as a function of radio-optical separation (a) for stellar objects and (b), (c) and (d) for galaxy samples with different magnitude limits.

 
Figure 3: A computer generated overlay of the MOST image (contours) on the Digitized Sky Survey (grey scale) for a complex radio source near the centre of the cluster A3785. The contour levels are -4, 4, 7, 10, 20, 50, 100, 200 and 600 mJy/beam. We expect that some or all of the radio emission is associated with the two brightest galaxies although their relative contributions are difficult to determine at this resolution.

 
Figure 4: Radial distribution of identified radio galaxies selected from 23 clusters on the basis of their absolute magnitudes (see text). The Abell radius is = 2000 kpc.

© Copyright Astronomical Society of Australia 1997