Figure 1 - uploaded by Edward J. Wollack
Content may be subject to copyright.
Cluster member galaxies with spectroscopic redshifts from Gemini identified on an SDSS r-band image. Blue boxes (red circles) denote members with higher (lower) redshifts than the systemic cluster redshift of z = 0.363. Large, bold symbols mark the BCGs of both kinematic components. The 148 GHz Compton y SZ contours are superposed. The contours start at a level of 2.0 × 10 −5 , increasing towards the centre in steps of 1.25 × 10 −5. The black X marks the cluster SZ peak.
Source publication
We present the detection of a giant radio halo (GRH) in the Sunyaev-Zel'dovich (SZ)-selected merging galaxy cluster ACT-CL
J0256.5+0006 (z = 0.363), observed with the Giant Metrewave Radio Telescope at 325 MHz and 610 MHz. We find this cluster to host a faint
(S610 = 5.6 ± 1.4 mJy) radio halo with an angular extent of 2.6 arcmin, corresponding to 0...
Contexts in source publication
Context 1
... this red- shift information, we can estimate an independent dynami- cal mass and re-examine the merger geometry proposed by M04 (see Section 5.2 below). The cluster members are shown in Figure 1 where red circles (blue boxes) denote members that are at lower (higher) redshifts than the cluster redshift of z = 0.363. We identify these two sets of galaxies as sep- arate kinematic components (see Section 5.2 below), each of which has a brightest cluster galaxy (BCG) that is indi- cated by a large, bold symbol. ...
Context 2
... there are two BCGs (cluster members with the lowest SDSS magnitudes) that are spatially separated, as seen from the SDSS image in Figure 1, which are also sepa- rated in velocity space as shown in Figure 9. This provides support for the existence of two distinct galaxy populations. ...
Context 3
... simplicity, we assume the same merger geometry as in M04, schematically outlined in Figure 10. Working in the rest frame of the main component, we assume the same simplification of a point mass subcluster and ignore dynamical friction. ...
Context 4
... implies that the impact angle must be less than 90 • . Using simple trigonometry, it follows from the merger geom- etry in Figure 10 that dmin d ...
Context 5
... solving equations 8 and 9 with these constraints provides two sets of solutions for the merger model. These are listed in Table 9, with the graphical so- lutions given in Figures 11 and 12. The uncertainties on v, d, and θ are shown in Figures 11 (v and d) and 12 (d and θ), and are propagated from the uncertainties on the R200 mass and radius of the main cluster component, the R200 radius of the subcluster, and measured line-of-sight velocity difference. ...
Context 6
... estimate the merger time-scales for J0256 we assume a simple merger taking place in a linear fashion along the merger axis determined by the impact angle, θ, schemati- cally outlined in Figure 13. In Section 2.1, we ruled out a scenario in which the subcluster has already passed through the core. ...
Context 7
... Section 2.1, we ruled out a scenario in which the subcluster has already passed through the core. In Figure 13, we isolate three distinct times during the merger: (A) first virial crossing; (B) core passage; and (C) second virial crossing. Even though we refer to virial crossing, we use R200 as a proxy for the virial radius. ...
Context 8
... case 1, J0256 is closer to the be- ginning of its merger with ∼460 Myr until first core passage. Figure 13. Schematic showing the relative position of the subcluster (red circles) to the main cluster (black circle) overlaid on the X-ray image at three different times during the merger: (A) first virial crossing; (B) core passage; and (C) second virial crossing. ...
Similar publications
The XXL Survey is the largest homogeneous and contiguous survey carried out
with XMM-Newton. Covering an area of 50 square degrees distributed over two
fields, it primarily investigates the large-scale structures of the Universe
using the distribution of galaxy clusters and active galactic nuclei as tracers
of the matter distribution. Given its dep...
We present a detection of the enhancement in the number densities of
background galaxies induced from lensing magnification and use it to test the
Sunyaev-Zel'dovich effect (SZE) inferred masses in a sample of 19 galaxy
clusters with median redshift $z\simeq0.42$ selected from the South Pole
Telescope SPT-SZ survey. Two background galaxy population...
We present Sunyaev-Zel'dovich (SZ) effect measurements from wide-field images towards the galaxy cluster RX J1347.5-1145 obtained from the Caltech Submillimeter Observatory with the Multiwavelength Submillimeter Inductance Camera (MUSIC) at 147, 213, 281, and 337 GHz and with Bolocam at 140 GHz. As part of our analysis, we have used higher frequenc...
Galaxy clusters contain a large population of low mass dwarf elliptical
galaxies whose exact origin is unclear: their colors, structural properties and
kinematics differ substantially from those of dwarf irregulars in the field. We
use the Illustris cosmological simulation to study differences in the assembly
paths of dwarf galaxies (3e8 < M_*/M_su...
We study the effects of filaments on galaxy properties in the Sloan Digital
Sky Survey (SDSS) Data Release 12 using filaments from the `Cosmic Web
Reconstruction' catalogue (Chen et al. 2015a), a publicly available filament
catalogue for SDSS. Since filaments are tracers of medium-to-high density
regions, we expect that galaxy properties associated...
Citations
... The upper limit to the spectral index implied by our ASKAP and ATCA maps is also far steeper than the typical spectral index of many radio haloes (e.g. Dallacasa et al. 2009 ;Knowles et al. 2016 ;Shweta, Athreya & Sekhar 2020 ;Wilber et al. 2020 ;Bruno et al. 2021 ;Duchesne et al. 2021b,d ;Rajpurohit et al. 2021a , b ). Thus, the nature of this source is not immediately obvious. ...
Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8–1.1 GHz) and the Australia Telescope Compact Array (1.1–3.1 GHz). These deep observations provide new insights into recently reported diffuse non-thermal phenomena associated with the intracluster medium, including a ‘wrong-way’ relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest part of a large-scale radio halo detected here for the first time. The ‘wrong-way’ relic is highly atypical of its kind: it exhibits many classical signatures of a shock-related radio relic, while at the same time exhibiting strong spectral steepening. While radio relics are generally consistent with a quasi-stationary shock scenario, the ‘wrong-way’ relic is not. We study the spectral properties of the fossil plasma source; it exhibits an ultrasteep and highly curved radio spectrum, indicating an extremely aged electron population. The larger scale radio halo fills much of the cluster centre, and presents a strong connection between the thermal and non-thermal components of the intracluster medium, along with evidence of substructure. Whether the central diffuse ridge is simply a brighter component of the halo, or a mini-halo, remains an open question. Finally, we study the morphological and spectral properties of the multiple complex radio galaxies in this cluster in unprecedented detail, tracing their evolutionary history.
... The upper limit to the spectral index implied by our ASKAP and ATCA maps is also far steeper than the typical spectral index of many radio haloes (e.g. Dallacasa et al. 2009;Knowles et al. 2016;Shweta et al. 2020;Wilber et al. 2020;Bruno et al. 2021;Duchesne et al. 2021b,d;Rajpurohit et al. 2021a,b). Thus, the nature of this source is not immediately obvious. ...
Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8$-$1.1 GHz) and the Australia Telescope Compact Array (1.1$-$3.1 GHz). These deep observations provide new insights into recently-reported diffuse non-thermal phenomena associated with the intracluster medium, including a 'wrong-way' relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest part of a large-scale radio halo detected here for the first time. The 'wrong-way' relic is highly atypical of its kind: it exhibits many classical signatures of a shock-related radio relic, while at the same time exhibiting strong spectral steepening. While radio relics are generally consistent with a quasi-stationary shock scenario, the 'wrong-way' relic is not. We study the spectral properties of the fossil plasma source; it exhibits an ultra-steep and highly curved radio spectrum, indicating an extremely aged electron population. The larger-scale radio halo fills much of the cluster centre, and presents a strong connection between the thermal and non-thermal components of the intracluster medium, along with evidence of substructure. Whether the central diffuse ridge is simply a brighter component of the halo, or a mini-halo, remains an open question. Finally, we study the morphological and spectral properties of the multiple complex radio galaxies in this cluster in unprecedented detail, tracing their evolutionary history.
... Recent GMRT 325 MHz and 610 MHz observations of the cluster (Knowles et al. 2016(Knowles et al. , 2019 revealed that the cluster does indeed host a faint radio halo. ...
We have used archival GMRT data to image and study 39 galaxy clusters. These observations were made as part of the GMRT Key Project on galaxy clusters between 2001 and 2004. The observations presented in this sample include 14 observations at 610 MHz, 29 at 325 MHz and 3 at 244 MHz covering a redshift range of 0.02 to 0.62. Multi-frequency observations were made for 8 clusters. We analysed the clusters using the SPAM processing software and detected the presence of radio halo emission for the first time in the clusters RXC J0510-0801 and RXC J2211.7-0349. We also confirmed the presence of extended emission in 11 clusters which were known from the literature. In clusters where halos were not detected upper limits were placed using our own semi-automated program. We plot our detections and non-detections on the empirical $L_X-P_{1.4}$ and $M_{500}-P_{1.4}$ relation in radio halo clusters and discuss the results. The best fits follow a power law of the form $L_{500} \propto P_{1.4}^{1.82}$ and $M_{500} \propto P_{1.4}^{3.001}$ which is in accordance with the best estimates in the literature.
... All statistical, uniformly-selected cluster samples used in radio halo studies have to date been restricted to high masses (M 500 6 × 10 14 M ) and lower redshift ranges ( 0.1 z < 0.4; e.g., Venturi et al. 2007;Cuciti et al. 2015), with current turbulent reaccleration formation theories predicting a sharp drop in the occurence of radio halos at higher redshift, where cluster magnetic fields are expected to be weaker (Cassano et al. 2006;Brunetti & Jones 2014). Diffuse emission has also been detected in some lowmass (e.g., Knowles et al. 2016b;Bernardi et al. 2016;Kale et al. 2017;Hlavacek-Larrondo et al. 2018;Brüggen et al. 2018;Hoang et al. 2020) and high-redshift (z > 0.5; Bonafede et al. 2009;Lindner et al. 2014;Pandey-Pommier et al. 2013;Riseley et al. 2017;Knowles et al. 2019;Giovannini et al. 2020) systems. Most of these detections result from single-target programmes or small samples. ...
The MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio Sources (MERGHERS) survey is a planned project to study a large statistical sample of galaxy clusters with the MeerKAT observatory. Here we present the results of a 16--hour pilot project, observed in response to the 2019 MeerKAT Shared Risk proposal call, to test the feasibility of using MeerKAT for a large cluster study using short (0.2--2.1 hour) integration times. The pilot focuses on 1.28 GHz observations of 13 massive, low-to-intermediate redshift ($0.22 < z < 0.65$) clusters from the Sunyaev-Zel'dovich-selected Atacama Cosmology Telescope (ACT) DR5 catalogue that show multiwavelength indications of dynamical disturbance. With a 70 per cent detection rate (9/13 clusters), this pilot study validates our proposed MERGHERS observing strategy and provides twelve detections of diffuse emission, eleven of them new, indicating the strength of MeerKAT for such types of studies. The detections (signal-to-noise ratio $>$ 6) are summarised as follows: two systems host both relic(s) and a giant radio halo, five systems host radio halos, and two have candidate radio halos.
... ZwCL5247). Lastly, in the last 2 yr, there has been a rapid increase in studies of individual or small samples of RH systems (see Bernardi et al. 2016;Girardi et al. 2016;Knowles et al. 2016;Duchesne et al. 2017;Hoang et al. 2017;Parekh et al. 2017;Venturi et al. 2017;Cuciti et al. 2018;Hlavacek-Larrondo et al. 2018;Wilber et al. 2018;Savini et al. 2019). We have collected measurements from these studies to form a larger sample of RHs. ...
... A1132, ACT-CL J0256.5+0006, CIZA J2242.8 + 5301; Knowles et al. 2016;Hoang et al. 2017;Wilber 8 X-ray luminosity, cluster mass, and SZ signal are calculated within R 500 , and the X-ray luminosity is measured in the 0.1-2.4 keV band. ...
The largest galaxy clusters are observed still to be forming through major cluster–cluster mergers, often showing observational signatures such as radio relics and giant radio haloes. Using LOFAR Two-meter Sky Survey data, we present new detections of both a radio halo (with a spectral index of |$\alpha _{143}^{1400}=1.48^{+0.06}_{-0.23}$|) and a likely radio relic in Abell 959, a massive cluster at a redshift of z = 0.288. Using a sample of clusters with giant radio haloes from the literature (80 in total), we show that the radio halo in A959 lies reasonably well on the scaling relations between the thermal and non-thermal power of the system. Additionally, we find evidence that steep-spectrum haloes tend to reside in clusters with high X-ray luminosities relative to those expected from cluster luminosity–mass(LM) scaling relations, indicating that such systems may preferentially lie at an earlier stage of the merger, consistent with the theory that some steep-spectrum haloes result from low-turbulence mergers. Lastly, we find that halo systems containing radio relics tend to lie at lower X-ray luminosities, relative to those expected from cluster LM scaling relations, for a given halo radio power than those without relics, suggesting that the presence of relics indicates a later stage of the merger, in line with simulations.
... Both samples are restricted to low to intermediate redshift and high mass systems. Diffuse radio emission has been detected in higher redshift and lower mass systems (Lindner et al. 2014;Knowles et al. 2016), but no systematic survey of a larger statistical sample of such systems has been undertaken. As inverse Compton (IC) losses are expected to dominate at high redshift (Marscher 1983), detecting diffuse radio emission above z = 0.5 has been predicted to be difficult in clusters below a mass of M500,SZ = 10 15 M (Cassano et al. 2010a). ...
... When determining flux densities for emission revealed in the source-subtracted, low-resolution images, we need to consider the effect of subtracting compact emission from the uv-data and to what extent the source subtraction contaminates the low resolution image. To this end we follow a similar procedure as in previous work (see Section 4.2 of Knowles et al. 2016) by performing a statistical analysis of the low resolution, source-subtracted images, using compact source and source-free positions. We summarise the main steps here. ...
... Our data revealed a radio halo in this cluster after removing the several compact radio sources from the cluster region. The detection is presented in detail in Knowles et al. (2016), where we measured a halo flux density of S610MHz = 5.6 ± 1.4 mJy. Since publishing the detection, where the halo was detected only in heavily smoothed images, we have reprocessed the radio data with updated software, leading to an improvement in the central noise of the full-resolution image of 15%. ...
We present Giant Metrewave Radio Telescope (GMRT) 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) clusters, including new data for nine. The sample includes 73 per cent of ACT equatorial clusters with M500 > 5 × 1014 M⊙. We detect diffuse emission in three of these (27$^{+20}_{-14}$ per cent): we detect a radio minihalo in ACT-CL J0022.2–0036 at z = 0.8, making it the highest redshift minihalo known; we detect potential radio relic emission in ACT-CL J0014.9–0057 (z = 0.533); and we confirm the presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux density S610 = 6.3 ± 0.4 mJy. We also detect residual diffuse emission in ACT-CL J0045.9–0152 (z = 0.545), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures; given the limited sensitivity of our observations, deeper observations of these disturbed systems are required in order to rule out the presence of diffuse emission consistent with known scaling relations. In parallel with our diffuse emission results, we present catalogues of individual radio sources, including a few interesting extended sources. Our study represents the first step towards probing the occurrence of diffuse emission in high-redshift (z ≳ 0.5) clusters, and serves as a pilot for statistical studies of larger cluster samples with the new radio telescopes available in the pre-SKA era.
... Both samples are restricted to low to intermediate redshift and high mass systems. Diffuse radio emission has been detected in higher redshift and lower mass systems (Lindner et al. 2014;Knowles et al. 2016), but no systematic survey of a larger statistical sample of such systems has been undertaken. ...
... When determining fluxes for emission revealed in the sourcesubtracted, low-resolution images, we need to consider the effect of subtracting compact emission from the uv-data and to what extent the source subtraction contaminates the low resolution image. To this end we follow a similar procedure as in previous work (see Section 4.2 of Knowles et al. 2016) by performing a statistical analysis of the low resolution, source-subtracted images, using compact source and sourcefree positions. We summarise the main steps here. ...
... Our data revealed a radio halo in this cluster after removing the several compact radio sources from the cluster region. The detection is presented in detail in Knowles et al. (2016), where we measured a halo flux of S 610MHz = 5.6 ± 1.4 mJy. Since publishing the detection, where the halo was detected only in heavily smoothed images, we have reprocessed the radio data with updated software, leading to an improvement in the central noise of the full-resolution image of 15%. ...
We present Giant Metrewave Radio Telescope 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) equatorial clusters, including new data for nine. The sample includes 11 of 15 ACT equatorial clusters (i.e., 73\%) with $M_{500} > 5 \times 10^{14}\;M_\odot$, and in three of 11 (27$^{+20}_{-14}$\%) we detect diffuse emission. We detect a $S_{610} = 2.1\;\pm\;0.2$ mJy radio mini-halo in ACT-CL J0022.2$-$0036 at $z=0.8$, making it the highest-redshift mini-halo known. We detect potential radio relic emission in ACT-CL J0014.9$-$0057 ($z=0.533$), and confirm the presence of a radio halo in the low-mass cluster ACT-CL J0256.5+0006, with flux $S_{610} = 6.3\;\pm\;0.4$ mJy. We also detect residual diffuse emission in ACT-CL J0045.9$-$0152 ($z=0.545$), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures; given the limited sensitivity of our observations (median central map noise 44 $\mu$Jy/beam), deeper observations are required to determine if diffuse radio emission is present in these disturbed systems. In parallel with our diffuse emission results, we present catalogs of individual radio sources, including a few interesting extended sources. Our study represents the first probe of the occurrence of diffuse emission in high-redshift ($z \gtrsim 0.5$) clusters, and serves as a pilot for statistical studies of larger cluster samples with the new radio telescopes available in the pre-SKA era.
... h the halo detections in this paper. Error bars have been omitted for the sake of clarity. The black unfilled circles are haloes from the literature, drawing from the same sample asShakouri et al. (2016) with the addition of the haloes detected in Triangulum Australis(Scaife et al. 2015), MACS J2243.3-0935(Cantwell et al. 2016), ACT-CL J0256.5+0006(Knowles et al. 2016), and PSZ1 G285.0-23.7 (MartinezAviles et al. 2016) ...
We detect and characterise extended, diffuse radio emission from galaxy clusters at 168 MHz within the Epoch of Reionization 0-hour field; a $45^\circ \times 45^\circ$ region of the southern sky centred on R. A. $= 0^\circ$, decl. $=-27^\circ$. We detect 31 diffuse radio sources; 3 of which are newly detected haloes in Abell 0141, Abell 2811, and Abell S1121; 2 newly detected relics in Abell 0033 and Abell 2751; 5 new halo candidates and a further 5 new relic candidates. Further, we detect a new phoenix candidate in Abell 2556 as well as 2 candidate dead radio galaxies at the centres of Abell 0122 and Abell S1136 likely associated with the brightest cluster galaxies. Beyond this we find 2 clusters with unclassifiable, diffuse steep-spectrum emission as well as a candidate double relic system associated with RXC J2351.0-1934. We present measured source properties such as their integrated flux densities, spectral indices, and sizes where possible. We find several of the diffuse sources to be ultra-steep including the halo in Abell 0141 which has $\alpha \leq -2.1 \pm 0.1$ making it one of the steepest halos known. Finally, we compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power ($P_{1.4}$) with the cluster X-ray luminosity ($L_{\mathrm{X}}$) and mass ($M_{500}$). We find consistent fitting parameters for assumed power law relationships, and find that the $P_{1.4}-L_{\mathrm{X}}$ has less raw scatter than the corresponding $P_{1.4}-M_{500}$ despite inhomogeneous $L_{\mathrm{X}}$ measurements. These scaling relation properties are consistent with a sample of only non-cool core clusters hosting radio haloes.
Clusters of galaxies are merging during the formation of large-scale structures in the Universe. Based on optical survey data, we identify a large sample of pre-mergers of galaxy clusters and merging subclusters in rich clusters. We find 39,382 partners within a velocity difference of 1500 km/s and a projected separation of 5r_{500} around 33,126 main clusters, where r_{500} is the radius of the main cluster. Based on the galaxy distribution inside rich clusters with more than 30 member galaxy candidates, we identify subclusters by modeling the smoothed optical distribution with a two-component profile, and a coupling factor is obtained for merging subclusters in 7845 clusters. In addition, we find 3446 post-collision mergers according to the deviations of brightest cluster galaxies from other member galaxies, most of which have been partially validated by using the Chandra and XMM-Newton X-ray images. Two new bullet-like clusters have been identified by using the optical and X-ray images. The large samples of merging clusters of galaxies presented here are important databases for studying the hierarchical structure formation, cluster evolution, and the physics of intergalactic medium.
Low frequency radio observations of galaxy clusters are a useful probe of the non-thermal intracluster medium (ICM), through observations of diffuse radio emission such as radio halos and relics. Current formation theories cannot fully account for some of the observed properties of this emission. In this study, we focus on the development of interferometric techniques for extracting extended, faint diffuse emissions in the presence of bright, compact sources in wide-field and broadband continuum imaging data. We aim to apply these techniques to the study of radio halos, relics and radio mini-halos using a uniformly selected and complete sample of galaxy clusters selected via the Sunyaev-Zel’dovich (SZ) effect by the Atacama Cosmology Telescope (ACT) project, and its polarimetric extension (ACTPol). We use the upgraded Giant Metrewave Radio Telescope (uGMRT) for targeted radio observations of a sample of 40 clusters. We present an overview of our sample, confirm the detection of a radio halo in ACT−CL J0034.4+0225, and compare the narrowband and wideband analysis results for this cluster. Due to the complexity of the ACT−CL J0034.4+0225 field, we use three pipelines to process the wideband data. We conclude that the experimental spam wideband pipeline produces the best results for this particular field. However, due to the severe artefacts in the field, further analysis is required to improve the image quality.
