Diffuse bubble-like radio-halo emission in MRC 0116+111: Imprint of AGN feedback in a distant cluster of galaxies

arXiv:0903.0065v1 [astro-ph.CO] 28 Feb 2009 The Low-Frequency Radio Universe ASP Conference Series, Vol. LFRU, 2009 Eds: D.J. Saikia, Dave Green, Y. Gupta and Tiziana Venturi Diffuse bubble-like radio-halo emission in MRC 0116+111: Imprint of AGN feedback in a distant cluster of galaxies Joydeep Bagchi1, Joe Jacob2, Gopal-Krishna3, Nitin Wadnerkar4, J. Belapure5, Norbert Werner6, A.C. Kumbharkhane4 1IUCAA, Pune University Campus, Pune 411007, India 2Newman College, Thodupuzha 685585, Kerala, India 3NCRA - TIFR, Pune University Campus, Pune 411007, India 4School of Physical Sciences, S.R.T.M. University, Nanded 431606, India 5Dept. of Physics, Pune University, Pune 411007, India 6Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USA Abstract. We report the discovery of a luminous, mini radio halo of ∼240 kpc dimension at the center of a distant cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA observations reveal a highly unusual structure showing a twin bubble-like diffuse radio halo surrounding a cluster of bright elliptical galaxies; very similar to the large-scale radio structure of M87, the dominant galaxy in Virgo cluster. It presents an excellent opportu- nity to understand the energetics and the dynamical evolution of such radio jet inflated plasma bubbles in the hot cluster atmosphere. 1. Introduction Recent X-ray observations with Chandra and XMM-Newton have revealed a surprising aspect of cooling flows in clusters; they showed far less cooling be- low X-ray temperatures than expected, altering the previously accepted picture of cooling flows (Peterson & Fabian 2006). Unless gas is thermally supported, radiative cooling leads to a ‘cooling catastrophe’, i.e. inexorable inflow of cold gas onto the central galaxy. To prevent this, some heating mechanism was required to raise gas temperature above∼2 keV, supressing the cooling flow. Although several such mechanisms were discussed, the most effective heating process is the energy injected into the intra-cluster medium (ICM) by radio jets from AGNs of central galaxies of clusters and groups (Binney & Tabor 1995; Churazov et al. 2001) . Almost all cool-core clusters harbour powerful central AGNs (Burns 1990) which suggests that they are fuelled by accretion of cooling gas (Bagchi & Kapahi 1994; Allen et al. 2006), with the flow rate itself regulated by AGN-heating (Churazov et al. 2001). Many details of how this AGN-ICM feedback process works are still far from clear. Radio jets from a central AGN would inflate two bubble-like lobes of non-thermal plasma, filled with relativis- tic particles and magnetic field, and thus become visible in radio observations (Gull & Northover 1973). Such non-thermal bubbles are visible in radio and X- ray observations; such as those in clusters MS0735.6+7421, Hydra-A, and others, 1 2 Figure 1. left: GMRT 1.28 GHz map of MRC 0116+111 (contour levels: ±0.24, 0.48, 0.96, 2, 4, 8 mJy/beam, beam FWHM: 5′′ circular) overlayed on IGO R-band image. No AGN (radio core) is visible down to ∼1 mJy/beam flux density limit, and no radio jets or lobes are detectable. right: Low and high frequency spectral index maps of MRC 0116+111from combining the GMRT maps at 240 and 621 MHz (on left) and VLA maps at 1425 and 4860 MHz (on right). Both pairs of maps have the matched resolution of 12′′ (FWHM). Only pixels ∼3.5 times above the noise level were included by giving cut-offs at values 4 mJy/beam, 0.5 mJy/beam, 0.27 mJy/beam and 0.15 mJy/beam on 240, 621, 1425 and 4860 MHz maps respectively. showing an unusually large and energetic pair of radio emitting, X-ray dark cavi- ties (e.g., McNamara et al. (2000, 2005); McNamara and Nulsen (2007)). These synchrotron plasma bubbles are resposible for the mechanical (PdV) work on the ICM for heating it, which is one of the suggested mechanism of AGN-ICM feed- back. Therefore, observations of bubble-like, diffuse radio sources near cluster centres can provide crucial data for understanding this important astrophysical process. 2. Optical & radio observations: physical picture of the source An early report on a diffuse radio source MRC 0116+111 matching the charac- teristics of a mini-halo, was presented by some of us, based on VLA and GMRT observations (Gopal-Krishna et al. 2002). Recently, a distant galaxy cluster was reported at the position of MRC 0116+111 (Lopes et al. 2004). Here we re- port higher sensitivity GMRT observations made at 1.28 GHz, 621 MHz and 240 MHz frequencies using the 128 channel FX correlator. The earlier VLA observations made in C-band (DnC array) and L-band (CnB array) have been reanalysed. Optical broadband (B,V,R,I) CCD imaging observations were taken with IFOSC on the 2 mt telescope at the IUCAA Girawali Observatory (IGO). For spectroscopy we used the ESO 3.6 mt New Technology Telescope (NTT) and EMMI (ESO Multi-Mode Instrument). A low resolution slit-spectrum was taken with the g

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