The Radio/X-Ray Connection in Abell 2029

X-Ray and Radio Connections www.aoc.nrao.edu/events/xraydio Santa Fe NM, 3-6 February 2004 (7.8) 1 THE RADIO/X-RAY CONNECTION IN ABELL 2029 T. E. Clarke, E. L. Blanton, C. L. Sarazin Department of Astronomy, Univ. of Virginia P.O. Box 3818, Charlottesville, VA 22903 [email protected] Abstract in cooling core clusters often reveal compact steep- spectrum morphology. X-ray observations of clusters We present results of an analysis of the central regions such as Perseus (Bohringer¨ et al., 1993; Fabian et al., of Abell 2029 and discuss the connections between 2000), Hydra A (McNamara et al., 2000) and Abell the radio and X-ray components of the cluster. De- 2052 (Blanton et al., 2001) with ROSAT and Chan- spite the very relaxed appearance of the thermal gas dra show cavities (or bubbles) in the thermal gas that in the outer cluster regions, the Chandra observations appear to be spatially co-incident with the radio lobes reveal significant structure in the cluster core. There of the powerful cluster-center radio sources. The in- are a number of bright X-ray filaments as well as a terplay between the thermal and radio plasma is com- spiral “excess”. Several of the filaments appear to be plex. Contrary to predictions of supersonic expansion connected to the steep-spectrum cluster-center radio of radio sources (Heinz, Reynolds & Begelman, 1998), source PKS 1508+059. An analysis of the tempera- the Chandra observations of these cluster systems do ture structure in the cluster shows that the southern ex- not reveal the presence of hot gas due to shocks near tension of PKS 1508+059 is surrounded by cool X-ray the radio lobes, rather the radio sources are often sur- gas, while the northern lobe apparently lies in a region rounded by dense rims of cool gas. These observations of average temperature. We also discuss the inner re- indicate that the radio sources appear to be expanding gions of the radio source which show two oppositely- subsonically into the ICM and displacing the thermal directed, collimated jets that disrupt as the jets appar- gas (Fabian et al., 2000; McNamara et al., 2000). This ently encounter a drop in the confining thermal plasma. slow displacement of the X-ray gas results in the dense, bright rims of cool gas surrounding the (at least par- 1 Introduction tially) evacuated cavities. The cool nature of this gas is On global scales the thermal gas in galaxy clusters suggested by the soft X-ray spectrum as well as opti- traces the structure in the cluster's gravitational poten- cal emission lines associated with the X-ray rims seen tial. In the outer regions of a relaxed cluster the X- in some cluster systems (Blanton et al., 2001; McNa- ray emission is relatively smooth and symmetric, while mara et al., 2000). In turn, the dense cluster medium the inner regions often show very peaked X-ray emis- is thought to confine the radio source and produce the sion which is generally interpreted as a cooling flow (edge darkened) FRI structure typical of cooling flow (Fabian, 1994). The inner regions of these cooling cores. Equipartition arguments applied to the bubble flow clusters are often host to large central cD galax- systems suggest that the pressure in the radio lobes ies with powerful radio sources. The high-resolution is an order of magnitude less than the surrounding of the Chandra X-ray Observatory has revealed the de- thermal gas pressure (e.g., Hydra A, McNamara et al. tails of the complex interplay between the central radio 2000; Perseus, Fabian et al. 2000; Abell 2052, Blan- sources and the thermal intracluster medium (ICM). ton et al. 2001). Without some form of internal pres- In these dense cluster cores the radio source can pro- sure support (such as hot, diffuse thermal gas) these X-ray depressions would collapse on sound crossing foundly impact the structure of the thermal gas, while ¡ the confining thermal gas influences the structure and timescales of 10 yr. morphology of the radio source. Here, we present an analysis of the cluster Abell 2029. Radio sources associated with the dominant galaxy Abell 2029 is located at a redshift of ¢ = 0.0767 and 2 (7.8) X-Ray and Radio Connections www.aoc.nrao.edu/events/xraydio Santa Fe NM, 3-6 February 2004 contains the large central cD galaxy IC1101. Both the X-ray and optical emission are elongated along a north-east to south-west direction. The central galaxy is host to the wide-angle-tail radio source PKS 1508+059 which has two oppositely directed jets that £ £ disrupt at a distance of 10–15 from the cluster core (Sumi, Norman & Smarr, 1988). At larger radii, the radio emission is displaced south-west of the main jet structure forming a C-shaped source typical of merg- ing cluster systems. In standard wide angle tailed (WAT) radio sources, this C-shaped morphology is attributed to relative motions between the radio galaxy and the surrounding intergalactic medium. It has been argued that the orbital motions of a cluster-core cD radio galaxy are too small to produce the distortions (Eilek et al. 1984; O'Donoghue et al. 1993). In clas- sical swept-back cluster-core sources, the morphology is therefore often attributed to a merger where the ICM Figure 1: Adaptively smoothed 0.3–10.0 keV Chandra im- is moving past the radio source (Burns et al. 1994). age of the entire S3 chip of Abell 2029. The entire image is roughly 780 kpc on a side. The X-ray surface bright- On large scales, the thermal emission in Abell 2029 ness shows that the overall cluster emission is elongated in shows an exceptionally relaxed structure. Previous X- a north-east to south-west direction. The large scale emis- ray observations have revealed large inferred cooling- sion is very smooth indicating a relaxed cluster morphology. ¤ ¥ ¦ ¥¨§ flow rates for Abell 2029 of 100 yr © (e.g., Sarazin, O'Connell & McNamara, 1992; Edge, Stew- The cluster-center radio galaxy PKS 1508+059 was art & Fabian, 1992; Peres et al., 1998; Sarazin, Wise observed by Taylor, Barton & Ge (1994) with the Very & Markevitch, 1998, although see also White 2000; Large Array at a variety of frequencies. They provide Lewis, Stocke & Buote 2002) and have suggested the a detailed spatial and spectral analysis of the source in presence of X-ray filaments associated with the central their paper. In this paper, we concentrate on the 1.4 radio source (Sarazin, O'Connell & McNamara, 1992; and 8.4 GHz observations from Taylor et al. Taylor, Barton & Ge, 1994). The apparently relaxed, cooling flow thermal structure is in apparent conflict 3 Cluster properties with the presence of the C-shaped central radio source. © © We assume H = 71 km s Mpc , = 0.73, and Optical observations of the central cD galaxy IC1101 £ £ = 0.27. At the redshift of Abell 2029, 1 corre- in Abell 2029 trace the diffuse light out to radii of more sponds to a linear scale of 1.44 kpc. than 600 kpc from the cluster core (Uson, Boughn & Kuhn, 1991), making it one of the largest known 2 Radio and X-ray data galaxies. Observations of the cluster by McNamara & O'Connell (1989) reveal that it has no optical emis- The galaxy cluster Abell 2029 was observed on 2000 sion lines or blue stellar continuum in the core. The April 12 with Chandra for a total of 19.8 ks. The lack of optical indications of star formation is unusual observations were centered on the S3 chip which in a cooling core as many of these systems reveal opti- was operating at 120 C. The archival observations cal nebulosity indicating the presence of star formation (observation ID 891) were extracted from the Chan- (e.g., McNamara & O'Connell, 1989). dra archive and reprocessed using CIAO v2.3 and Figure 1 shows the adaptively smoothed Chandra 0.3– CALDB v2.18. The back-illuminated S1 chip was 10.0 keV image of the entire S3 chip. The X-ray used to examine the background during the observa- emission appears very smooth and symmetric on large tions since the cluster emission fills the entire S3 chip. scales, consistent with the presence of a central cooling The data were free of large flares and only 128 s of data core. There are no obvious X-ray surface brightness were removed. features that indicate the presence of a major cluster X-Ray and Radio Connections www.aoc.nrao.edu/events/xraydio Santa Fe NM, 3-6 February 2004 (7.8) 3 lor, Barton & Ge, 1994). The steep spectral index and edge-darkened morphology are consistent with con- finement of the radio source by the dense thermal intracluster medium. The inner X-ray jets appear to propa- gate along the pinch axis of the core and are connected to the outer lobes by faint synchrotron bridges. The spectral index of the outer lobes steepens to 3.0. A typical extragalactic radio source has a spectral index of = 0.7. The steep-spectrum southern radio lobe is partially surrounded by a bright X-ray rim which may be similar to the rims seen in sources such as Perseus (Fabian et al., 2000) and Abell 2052 (Blanton et al., 2001). An analysis of the X-ray data shows that the filament is a 9 excess over the average counts in an annulus the width of the filament centered on the cluster core. The thermal pressure in the X-ray filament was determined by Figure 2: Adaptively smoothed 0.3–10.0 keV Chandra im- extracting a rectangular region set on the filament and age of the central 1.5 arcminute (130 kpc) region of Abell 2029.

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