D. McConnell ,
R. Deacon ,
J.G. Ables
, PASA, 18 (2), in press.
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Title/Abstract Page: Radio Images of the
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Image Analysis and Results
We describe the analysis and results from the 1.4 GHz image. (The same reduction procedures were used for the 1.7 GHz image and its relevance in this paper is restricted to the measurement of spectral indices of sources in the cluster centre.) Over the 53 field (2208 arcmin2) the image noise fluctuations range from
18 over the cluster centre to 60 at the field edge. Within this area 305 sources were detected above the 5 threshhold. After correction for the varying sensitivity across the field we found a mean density of sources with S1.4 > 90 of 0.250.01 arcmin-2. The sensitivity to radio sources is limited by image fluctuations originating from thermal noise in the receiving equipment and radiation from the sky and ground. The detectability of weak sources is also limited by the extent to which corrections can be made for the sidelobe response to strong sources in the field. While image fluctuations are dominated by sources of random noise the sensitivity is expected to improve with integration time T as
. The image formed from the 1992 observations had an effective integration time on the cluster core of 33 hours and at 1.4 GHz the image rms was 42 . The new image has T = 170 hours and
18 close to the value expected from the
relation. Note that this is well above the rms value of 10 expected from considering only the thermal contributions to noise.
(1) | (2) | (3) | (4) | (5) |
Source | S1.4 | S1.7 | ||
() | () | |||
C | 4 | 243 | 122 | -3.60.8 |
D | 8 | 369 | 200 | -3.20.5 |
E | 84 | 61 | -1.72.1 | |
F | 176 | 50 | -6.52.2 | |
G/I | 102 | 65 | -2.31.9 | |
J | 5 | 330 | 202 | -2.50.5 |
L | 95 | 79 | -1.01.7 | |
O | 77 | (22) | (-6.47) | |
Q | 116 | 59 | -3.52.3 | |
U | 114 | (28) | (-7.35.4) | |
142 | 3 | 727 | 628 | -0.80.2 |
176 | 7 | 202 | 201 | 0.00.7 |
178 | 92 | 116 | 1.21.4 | |
183 | 108 | 36 | -5.75.5 | |
186 | 101 | 59 | -2.82.2 |
Table 2 gives, for each source in Figure 1, measured values of flux at 1.4 GHz and 1.7 GHz and their spectral indices. The relatively large uncertainties in spectral index result from the small frequency separation of the flux measurements and the low signal-to-noise ratio for most sources.
Next Section: Discussion
Title/Abstract Page: Radio Images of the
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© Copyright Astronomical Society of Australia 1997