The Eta Carinae Nebula and Centaurus A Near 1400mc/s. I. Observations

Abstract

Observations of two strong southern radio sources, the Eta Carinae Nebula (NGC 3372) and Centaurus A (13S4A), at a frequency near 1400 Mc/s, are described. The observations were made with a 36 ft transit-mounted paraboloidal aerial and a 21 cm hydrogen-line receiver modified for the reception of continuum radiation. The flux density of the Eta Carinae Nebula near 1400Mc/sis5� 82 X 10-24Wm-2 (c/s)-\ with an estimated uncertainty of less than �20 per cent. This source appears to be fairly symmetrical, with a strong central condensation.

A Study of the Decimetric Emission and Polarization of Centaurus A

“…By this time, the general structure of the source had been determined, and further measurement was primarily for the investigation of the brightness distribution with the higher resolution instruments that were coming into use, and for the study of the brightness distribution as a function of frequency. Hindman and Wade (1959) studied the source at 1400 Mc/s and further confirmed the previously determined structure, their observations bearing "a remarkably close resemblance" to findings at lower frequencies. Wade (1959) interpreted previous investigations as indicating that the extended source of low brightness temperature was a "double" source of radio emission, with the intense source (and NGC 5128) lying approximately midway between the two peaks of the extended source.…”

“…Hindman and Wade (1959) studied the source at 1400 Mc/s and further confirmed the previously determined structure, their observations bearing "a remarkably close resemblance" to findings at lower frequencies. Wade (1959) interpreted previous investigations as indicating that the extended source of low brightness temperature was a "double" source of radio emission, with the intense source (and NGC 5128) lying approximately midway between the two peaks of the extended source. Bolton and Clark (1960) applied a similar analysis to their 960 Mc/s observations and derived a similar brightness distribution for the extended source.…”

The Extended Component of Centaurus A

“…Early interferometric observations (Mills 1953;Bolton et al 1954) indicated that the radio source comprises two distinct components: an intense source with an angular size of a few minutes of arc, coincident in position with NGC 5128 ; and a much fainter source of far greater size surrounding NGC 5128. This has been confirmed by subsequent pencil-beam observations at 19•7 Mc/s ), 85•5 Mc/s (Sheridan 1958, and 1400 Mc/s (Hindman and Wade 1959;Heeschen, personal communication). These show that the extended component covers a solid angle of more than 20 square degrees; that it subtends about 8° of declination and 3° of Right Ascension; and that NGC 5128 lies near its centre.…”

“…Source b was resolved well in the original observations, but the beam-broadened radiation of Source a effectively masked Source c. One should not attach too much significance to the finer details in Figure 3, The fact that the central source accounts for some 25 per cent. of the total flux at both 85•5 and 1400 Mc/s (Hindman and Wade 1959) implies that Source a and the extended component both have similar spectral laws at metre and decimetre wavelengths. On the other hand, Source a contributes only 11 per cent.…”

Early Australian Optical and Radio Observations of Centaurus A

“…They found that the source extended ,7 deg in declination and ,3 deg in RA with a similar distribution to that observed by Sheridan at 85.5 MHz. Hindman & Wade (1959) found the total flux density of the source to be 1.3 Â 10 4 Jy, and that 23% of this could be attributed to the central source (see Figure 42).…”