3.3 Results
3.3.1 Clusters without diffuse emission
3.3.1.2 Radio environments
Table 3.6: Results of the survival analysis for theP1.4GHzvsM500relation, on three combinations of the data.
Statistic Literature only Lit. + original UL Lit. + revised UL
CI <0.1% <0.1% <0.1%
χ2 13.531 17.134 18.050
intercept -16.202±7.693 -17.870±6.959 -21.455±7.062 slope 2.732±0.516 2.842±0.467 3.080±0.474
standard deviation 0.375 0.370 0.383
Table 3.7: Compact sources in the ACT-CL J0014.9−0056 cluster region. The spectral index is determined using the FIRST source flux when available.
ID R.A. Dec. S610MHz α1400610 Optical
(hms) (hms) (mJy) counterpart
S1 00 14 52.23 −00 57 20.11 35.73±0.12 1.04 CM S2 00 14 54.08 −00 57 09.70 1.53±0.07 – CM (BCG) S3 00 14 51.54 −00 57 45.11 0.87±0.06 – CM
Figure 3.10: GMRT 610 MHz maps of the cluster regions for ACT-CL J0014.9−0056 (left) and ACT-CL J0022.2−0036 (right). In each panel, the dashed circle indicates theR500cluster scale, with the cross showing the SZ peak.
are provided in Table 3.7, with the GMRT radio map of the cluster region given in the left panel of Figure 3.10.
ACT-CL J0022.2−0036
There are three sources detected at 610 MHz in the cluster region, shown in the right panel of Figure 3.10. Their details are given in Table 3.8. Only the brightest source is detected in FIRST, which is also matched with the cluster BCG in the SDSS DR12 image. S2 has a foreground optical counterpart.
ACT-CL J0045.2−0152
The cluster region at 610 MHz is host to three compact sources, the details of which are given in Table 3.9. All three sources are detected in FIRST and all are matched with potential cluster members in the SDSS DR12 image. The 610 MHz radio map of the cluster region is shown in the left panel of Figure 3.11.
Table 3.8: Compact sources in the ACT-CL J0022.2−0036 cluster region. The spectral index is determined using the FIRST source flux when available.
ID R.A. Dec. S610MHz α1400610 Optical
(hms) (hms) (mJy) component
S1 00 22 12.96 −00 36 31.95 33.59±0.16 0.68 CM (BCG) S2 00 22 17.04 −00 36 31.75 0.29±0.06 – FG S3 00 22 13.79 −00 35 59.21 0.17±0.06 – –
Table 3.9: Compact sources in the ACT-CL J0045.2−0152 cluster region. The spectral index is determined using the FIRST source flux when available. Optical counterparts are defined as being a foreground (FG) source or a possible cluster member (CM) based on optical colours in the SDSS DR12 image.
ID R.A. Dec. S610MHz α1400610 Optical
(hms) (hms) (mJy) counterpart
S1 00 45 12.28 −01 52 33.55 13.72±0.11 1.32 CM (BCG) S2 00 45 11.45 −01 53 10.22 4.83±0.08 1.01 CM S3 00 45 15.95 −01 53 41.05 4.69±0.09 1.06 CM
The radio galaxy NGC 0245 (J2000 R.A. = 00h46m05.35s, Dec. = −01d43m24.35s) lies within the GMRT field-of-view of ACT-CL J0045.2−0152. NGC 0245 is a nearly face-on spiral galaxy at z = 0.0136. It has been identified as a metal-rich starburst galaxy, with recent star formation occurring in the galaxy nucleus as well as in regions of the spiral arms (P´erez-Gonz´alez et al., 2003). It is part of several galaxy samples studied in the infrared and near and far ultraviolet wave bands (Moshir et al., 1990; Rego et al., 1993; Moustakas and Kennicutt, 2006; Hao et al., 2011).
In our 610 MHz map, we detect the bright core of NGC 0245, S610,core = 7.83±0.05mJy, surrounded by a halo of faint diffuse emission of radius 0.570 (9.5 kpc at the galaxy redshift of z = 0.0136). The right panel of Figure 3.11 shows our 610 MHz radio contours for this galaxy, overlaid on the 3-colourgriimage from SDSS Data Release 12 (Alam et al., 2015). The diffuse emission traces the spiral arms, with radio hot spots roughly coinciding with the regions of star forming activity. The flux of the entire object isS610 = 65.17±0.42mJy. The galaxy features
08.0 07.0 06.0 0:46:05.0 04.0 03.0
-1:43:00.030.044:00.0
Right ascension
Declination
Figure 3.11: Left: GMRT 610 MHz map of the cluster region of ACT-CL J0045.2−0152. The dashed circle indicates theR500cluster scale, with the cross showing the SZ peak. Right:GMRT 610 MHz image of the radio galaxy NGC0245 which lies within the field of view of our J0045 observation.
are unresolved in NVSS, with the entire object having a flux ofSNVSS = 38.2±1.9mJy. This gives a global source spectral index of α610NVSS = 0.64. The diffuse emission surrounding the radio galaxy is not detected in FIRST, although two hotspots in the spiral arms are detected, with FIRST fluxes of 5.6 ± 0.3 mJy and 4.9 ± 0.2 mJy respectively. With its smaller synthesised beam, FIRST also resolves the central core, but it has a higher flux ofSFIRST,core = 8.16±0.4 mJy compared to the GMRT 610 MHz flux, leading to a spectral index ofαFIRST610,core =−0.05. An inverted radio spectrum has been found in the nucleus of another star forming galaxy, NGC 4418 (α5GHz1.4GHz = −0.7, Varenius et al., 2014). The authors suggest that the inversion could be due to flux attenuation from AGN activity at the lower frequency (in their case 1.4 GHz), in the form of synchrotron self-absorption, or thermal free-free absorption in the foreground. If a similar scenario is present in NGC 0245, high resolution imaging with Very Long Baseline Interferom- etry (VLBI) would be necessary to reveal AGN activity within its nucleus. The FIRST source positions are indicated by red squares in the right panel of Figure 3.11.
Figure 3.12: GMRT 610 MHz maps of the cluster regions for ACT-CL J0059.1−0049 (left) and ACT-CL J2135.7+0009 (right). In each panel, the dashed circle indicates theR500cluster scale, with the cross showing the SZ peak.
ACT-CL J0059.1−0049
There are only two compact sources in the cluster region, neither of which is detected in FIRST or NVSS. S1 appears to be the cluster BCG based on optical matching in the SDSS DR12 image.
The 610 MHz source details are provided in Table 3.10, with the 610 MHz radio image of this region shown in the left panel of Figure 3.12.
The field-of-view is dominated by a bright source to the East of the cluster region, positioned at R.A. = 00h59m30.10s, Dec. =−00d46m12.74s, as can be seen in Figure A.4. The 610 MHz flux of this source is 465.18± 0.11 mJy. It is detected in both NVSS and FIRST, providing a spectral index measurement ofα= 0.92.
ACT-CL J2135.7+0009
This is a low redshift cluster (z= 0.117) and it hence has a large angular size of 7.30(R500 = 930 kpc), shown in the right panel of Figure 3.12. However, there are only two sources in this region, only one of which is above the detection threshold of FIRST. Both sources have optical coun-
Table 3.10: Compact sources in the ACT-CL J0059.1−0049 cluster region. Neither of the sources is detected in FIRST or NVSS. Optical counterparts are defined as being a foreground (FG) source or a possible cluster member (CM) based on optical colours in the SDSS DR12 image.
ID R.A. Dec. S610MHz Optical
(hms) (hms) (mJy) counterpart
S1 00 59 08.52 −00 50 07.01 0.94±0.06 CM (BCG) S2 00 59 08.90 −00 49 22.80 0.34±0.06 –
Table 3.11: Compact sources in the ACT-CL J2135.7+0009 cluster region. The spectral index is determined using the FIRST source flux when available. Optical counterparts are defined as being a foreground (FG) source or a possible cluster member (CM) based on optical colours in the SDSS DR12 image.
ID R.A. Dec. S610MHz α1400610 Optical
(hms) (hms) (mJy) counterpart
S1 21 35 39.71 00 09 48.36 33.14±0.29 1.01 CM (BCG) S2 21 35 36.43 00 11 29.16 1.77±0.17 – FG
terparts in the SDSS DR12 image, one of which appears to be the cluster BCG. The 610 MHz source details are given in Table 3.11.
ACT-CL J2154.5−0049
The 610 MHz field-of-view, shown in Figure A.7, is dominated by a 826.50±0.12 mJy source atα= 21h55m36.79s,δ=−00d47m55.96s. This source has a 1.4 GHz flux of 485.37 mJy and 465.6 ±14.0 mJy from FIRST and NVSS maps respectively, giving a source spectral index of α∼0.64−0.69.
The 610 MHz radio map of the cluster region is given in the left panel of Figure 3.13. There are only two sources detected in this region, neither of which are detected in FIRST or NVSS.
The brighter source has an optical counterpart in the SDSS DR12 image. The source details are given in Table 3.12.
Figure 3.13: GMRT 610 MHz maps of the cluster regions for ACT-CL J2154.5−0049 (left) and ACT-CL J2327.4−0204 (right). In each panel, the dashed circle indicates theR500cluster scale, with the cross showing the SZ peak.
ACT-CL J2327.4−0204
There are several compact radio sources in the 610 MHz map of the cluster region shown in the right panel of Figure 3.13. Their properties are given in Table 3.13. Only the brightest source (S4) is detected in FIRST. Most of the sources have an optical counterpart in the SDSS DR12 image.
The dominating source in the field-of-view is a bright, extended source identified as the active radio galaxy PKS 2324-02 at z = 0.1884. Figure 3.14 shows our 610 MHz radio map of PKS 2324-02 (top). The galaxy core is situated at a J2000 position of R.A = 23h26m53.843s, Dec. =
−02d02m13.09s and has a flux ofS610,core= 180.0±0.1 mJy in our 610 MHz GMRT, primary beam corrected map. Diffuse structures surrounding the galaxy core are oriented roughly NE to SW and have a largest angular extent of 2.40, corresponding to 454.5 kpc at the redshift of this source. This places this source below the size threshold of the rare giant radio galaxies (> 700 kpc, see e.g. Molina et al., 2014). The 610 MHz flux of the entire object isS610 = 4.439±0.003 Jy. There is bright compact emission within the NE lobe with a bridge of compact emission
4Using the NASA/IPAC Extragalactic Database:https://ned.ipac.caltech.edu/
Table 3.12: Compact sources in the ACT-CL J2154.5−0049 cluster region. None of the sources are identified in FIRST or NVSS, but there are several sources in the cluster region detected in the survey data that are not visible in the 610MHz map. Optical counterparts are defined as being a foreground (FG) source or a possible cluster member (CM) based on optical colours in the SDSS DR12 image.
ID R.A. Dec. S610MHz Optical
(hms) (hms) (mJy) counterpart
S1 21 54 32.51 −00 49 55.51 0.11±0.04 FG S2 21 54 36.06 −00 49 52.44 0.13±0.04 –
Table 3.13: Compact sources in the ACT-CL J2327.4−0204 cluster region. The spectral index is determined using the NVSS source flux when available. Optical counterparts are defined as being a foreground (FG) source or a possible cluster member (CM) based on optical colours in the SDSS DR12 image.
ID R.A. Dec. S610MHz α1400610 Optical
(hms) (hms) (mJy) counterpart
S1 23 27 24.37 −02 04 57.77 0.30±0.05 – – S2 23 27 29.38 −02 05 25.90 0.22±0.05 – FG S3 23 27 24.34 −02 04 14.37 0.25±0.05 – FG S4 23 27 28.15 −02 03 54.68 8.82±0.08 0.52 CM (BCG) S5 23 27 27.72 −02 04 11.15 2.24±0.06 – CM S6 23 27 26.81 −02 04 25.22 1.00±0.06 – CM S7 23 27 31.16 −02 04 23.72 0.20±0.06 – – S8 23 27 29.40 −02 03 23.71 0.29±0.07 – FG
joining it to the galaxy core. This bridge-like feature is also detected in the 1.4 GHz FIRST radio image of this galaxy, shown in the bottom left panel of Figure 3.14. The FIRST data shows similar structures within the diffuse emission as found in our 610 MHz map. The FIRST core flux isScore,FIRST = 144.3±0.3mJy, giving a relatively flat spectral index ofα1400610 = 0.27.
The radio images of PKS 2324-02 from NVSS and VLSS are shown in the bottom middle and right panels of Figure 3.14, respectively. None of the source structure can be resolved with the large beams of these surveys. Determining the NVSS and VLSS flux in a 2.40 circular aperture centred on the 610 MHz core givesSNVSS = 2.171±0.001 Jy and SVLSS = 16.85±0.13Jy,
Figure 3.14: Radio maps of active radio galaxy PKS 2324-02 which lies in the field of view of our ACT-CL J2327−0204 observations.Top:GMRT 610 MHz image with the presumed galaxy core indicated. Bottom: Archival radio images from FIRST (left, 1.4 GHz), NVSS (middle, 1.4 GHz), and VLSS (right, 74 MHz), with GMRT 610 MHz radio contours overlaid. Contours start at 2 mJy beam−1 and increase in steps of 4 mJy beam−1 until 30 mJy beam−1, after which they increase in steps of 30 mJy beam−1. The synthesised beam is shown as the boxed ellipse in the bottom left corner of each image.
respectively. We therefore have the following global spectral indices for PKS 2324-02: α1400610 = 0.86andα61074 = 0.63. A multiwavelength study of this source will form part of a future paper on the GMRT cluster sample.