J/MNRAS/324/1131 22-cm radio survey of A3528 (Venturi+, 2001)

J/MNRAS/324/1131/V//VBZ2001/notes.dat Individual notes to table4 (132 records)

[VBZ2001]
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Note
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J1254-2900 Is associated with the dominant cD galaxy in A3528N and is
J1254-2900 completely embedded within the envelope of the optical galaxy.
J1254-2900 Reid et al. (1998MNRAS.296..531R) classified this source as double,
J1254-2900 and high-resolution and high-frequency observations carried out
J1254-2900 with the Very Large Array (VLA) and ATCA (Venturi et al. in prep.)
J1254-2900 confirm that it is a mini-FR II radio source, with a radio nucleus
J1254-2900 and two jets culminating in hot spots, though its total power falls
J1254-2900 within the range of FR I radio galaxies. The source has a
J1254-2900 moderately steep spectrum over the frequency range of our
J1254-2900 observations, i.e. {alpha}^13^_22_=0.9.
J1254-2901aWas classified as a head-tail radio galaxy by Reid et al.
J1254-2901a (1998MNRAS.296..531R), who also postulated that the radio source
J1254-2901a may have been triggered by the passage of the galaxy close to the
J1254-2901a cluster centre. Inspection of the superposition between the radio
J1254-2901a image and the Digitized Sky Survey (Fig. 5) reveals that the radio
J1254-2901a peak is displaced from the centre of the optical counterpart. This
J1254-2901a is most likely a resolution effect, i.e. the nucleus of the radio
J1254-2901a emission is not coincident with the peak of our 22- and 13-cm
J1254-2901a images, but it could also be interpreted as an extreme effect of
J1254-2901a ram pressure exerted on the radio emission resulting from the
J1254-2901a galaxy motion through the very dense medium in the centre of
J1254-2901a A3528N. The source is extended ~60kpc east-west. The total spectral
J1254-2901a index of this source, computed in the range of frequencies
J1254-2901a presented in this paper, is {alpha}^13^_22_=1.2. We point out that
J1254-2901a it should be considered an upper limit, because the lack of short
J1254-2901a spacings at 13cm is likely to lead to an underestimate of the
J1254-2901a extended flux density. Furthermore the incomplete separation of
J1254-2901a this source from J1254-2900 at 22cm adds uncertainties in the
J1254-2901a 22-cm flux density.
J1254-2901bR=3.03 for this identification, however we consider it reliable
J1254-2901b because the rad io emission is extended (see Table 3) and the
J1254-2901b optical counterpart falls within the radio isodensity contours.
J1254-2904 Is a very interesting radio galaxy in A3528N. The source is
J1254-2904 ~4arcmin away from the cluster centre, in the region where the
J1254-2904 shock front between the two merging systems A3528N and A3528S is
J1254-2904 expected to be located (Schindler, 1996MNRAS.280..309S). The 13-cm
J1254-2904 image shows an extension in the direction of the galaxy #2063 (see
J1254-2904 also fig. 3 of Reid et al., 1998MNRAS.296..531R). On the assumption
J1254-2904 that this is the host galaxy we classify the radio source as a
J1254-2904 narrow-angle tail. This hypothesis is confirmed by observations at
J1254-2904 higher frequency and resolution (Venturi et al., in prep.), where
J1254-2904 the radio core is clearly detected. We therefore confirm the
J1254-2904 reliability of the tentative optical identification proposed by
J1254-2904 Reid et al. (1998MNRAS.296..531R). The source is extended
J1254-2904 ~1.5arcmin (i.e. ~65kpc). Its spectrum is steep in the range
J1254-2904 13-22cm, i.e. {alpha}^13^_22_=1.3, and flattens at lower
J1254-2904 frequencies. If we consider the VLA 92-cm flux density (Schindler,
J1254-2904 1996MNRAS.280..309S) and the MOST 36-cm data (Reid et al.,
J1254-2904 1998MNRAS.296..531R), we derive {alpha}^36^_92_=0.5 and
J1254-2904 {alpha}^22^_36_=1.1. We stress that the spectral index
J1254-2904 {alpha}^13^_22_ should be considered only an upper limit to its
J1254-2904 true value, because its extended morphology suggests that we may
J1254-2904 have lost extended flux at 13cm as a result of the poor short
J1254-2904 spacing u-v coverage of the present observations.
J1254-2913 Is the second most powerful radio galaxy in the A3528 complex and
J1254-2913 it is associated with the dominant cD galaxy in A3528S. The radio
J1254-2913 source is dominated by a strong compact component surrounded by
J1254-2913 extended emission, the shape of which is reminiscent of wide-angle
J1254-2913 tail sources (see also Reid et al., 1998MNRAS.296..531R). Its size,
J1254-2913 ~35x20kpc, barely exceeds the optical extent of the associated
J1254-2913 galaxy. Using the data at other wavelengths available in the
J1254-2913 literature (Reid et al., 1998MNRAS.296..531R, and Schindler,
J1254-2913 1996MNRAS.280..309S) we derive a spectral index 1.0, constant
J1254-2913 within the errors, in the range 92-13cm.
J1254-2916 is the weakest extended radio galaxy in the A3528 complex. The
J1254-2916 higher resolution 13-cm image (Fig. 6), together with the 92-cm VLA
J1254-2916 image from Schindler (1996MNRAS.280..309S), suggests that the
J1254-2916 source is a head-tail, with a faint compact component coincident
J1254-2916 with the associated cluster galaxy. Higher frequency and resolution
J1254-2916 observations (Venturi et al., in prep.) confirm that this is the
J1254-2916 nucleus of the radio galaxy. From our flux density measurements we
J1254-2916 derived a total flat spectrum with {alpha}^22^_13_=0.41. The source
J1254-2916 has low surface brightness and diffuse morphology in both bands
J1254-2916 presented in this paper, and comparison with the 20-cm total flux
J1254-2916 density obtained from inspection of the NVSS suggests that we may
J1254-2916 have lost extended flux both at 22 and 13cm. For this reason we
J1254-2916 believe that the derived spectral index should be taken with care.
J1254-2916 We point out that for the other extended sources we are presenting
J1254-2916 in this section, the NVSS 20-cm and the ATCA 22-cm flux density
J1254-2916 measurements are in good agreement (see Section 3.2). Given the
J1254-2916 uncertainty in the spectral index value, we defer any estimate of
J1254-2916 the physical parameters in J1254-2916 to a future paper.
J1257-3021 Is the most powerful radio galaxy in the A3528 complex, and is
J1257-3021 associated with the brighter nucleus of the dumb-bell galaxy
J1257-3021 located at the centre of A3532 (see Fig. 7). Its radio morphology
J1257-3021 is intermediate between FR I and FR II radio galaxies, consistent
J1257-3021 with its 22-cm total radio power. The peculiar asymmetric shape of
J1257-3021 the tails suggests that it could be a wide-angle tail source with
J1257-3021 its emission in a plane closely aligned with the line of sight to
J1257-3021 the observer. The core of the radio emission is undetectable both
J1257-3021 at 22cm and in the full-resolution 13-cm image. We used the 6-cm
J1257-3021 flux density value for this source given in Gregorini et al.
J1257-3021 (1994, Cat. <J/A+AS/106/1>), and computed the spectral index over
J1257-3021 the range 6-22cm, obtaining {alpha}~0.85, typical for this type of
J1257-3021 radio source.
J1254-3042 The 22-cm image of the radio source J1254-3042, shown in Fig. 8, is
J1254-3042 suggestive of a double-double type morphology (Lara et al.,
J1254-3042 1999A&A...348..699L) in the shape of a wide-angle tail; however,
J1254-3042 the optical identification is unclear, because two very faint
J1254-3042 objects coincide with the two inner peaks of the radio emission
J1254-3042 (see Table 4). From the 13-cm natural weighted image shown in
J1254-3042 Fig. 9, it is clear that the source is very asymmetric in this
J1254-3042 band, with the eastern lobe much fainter than the western one.
J1254-3042 We tentatively classified the radio source as a WAT.
J1255-2934 Has a typical FR II morphology, with a one-sided jet and two
J1255-2934 hotspots with similar flux density. The full resolution 13-cm image
J1255-2934 is given in Fig. 10. A very faint optical counterpart (see Table 4)
J1255-2934 is visible, close to the central radio peak between the two hot
J1255-2934 spots, but the identification with this object is uncertain. It is
J1255-2934 possible that the counterpart responsible for the radio emission is
J1255-2934 an absorbed high-redshift galaxy.
J1256-3009 The 22-cm radio density contours of J1256-3009 are shown in Fig. 11,
J1256-3009 superimposed on the DSS optical frame. This radio source has a
J1256-3009 linear morphology, with an extension of ~1.5arcmin. It is located
J1256-3009 north of the axis connecting the centres of A3530 and A3532, at a
J1256-3009 distance of ~14arcmin from the centre of A3530 and ~19arcmin from
J1256-3009 the centre of A3532. The DSS optical image shows the presence of a
J1256-3009 few faint optical objects in the vicinity of the radio emission,
J1256-3009 but none of them is obviously associated with the radio source.
J1256-3009 Unfortunately the source was not detected at 13cm, possibly because
J1256-3009 of its low surface brightness combined with lower sensitivity at
J1256-3009 its distance from the field centre (field #3), therefore no hint
J1256-3009 about its nature can be derived from the spectral index
J1256-3009 information. The source could be a double-double powerful radio
J1256-3009 galaxy associated with a distant object fainter than the DSS limit.
J1256-3009 Another possibility is that J1256-3009 is diffuse cluster emission
J1256-3009 within the Shapley Concentration. On this hypothesis the source
J1256-3009 would be ~60kpc in extent, with a power logP_22cm_(W/Hz)=22.87. We
J1256-3009 point out that J1256-3009 lies in the region where a merging shock
J1256-3009 arising from the interaction between A3530 and A3532 is expected.
J1256-3009 We plan to extend our study of this source in order to disentangle
J1256-3009 its nature.