MNRAS 000,1{9 (2017) Preprint 15 June 2017 Compiled using MNRAS LATEX style file v3.0 Deep 230-470 MHz VLA Observations of the Mini-Halo in the Perseus Cluster M. Gendron-Marsolais1?, J. Hlavacek-Larrondo1, R. J. van Weeren2, T. Clarke3, A. C. Fabian4, H. T. Intema5, G. B. Taylor6, K. M. Blundell7 and J. S. Sanders8 1D´epartement de Physique, Universit´ede Montr´eal, Montr´eal, QC H3C 3J7, Canada 2Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 3Naval Research Laboratory, Code 7213, 4555 Overlook Ave. SW, Washington, DC 20375, USA 4Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA 5Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333CA, Leiden, The Netherlands 6Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USA 7University of Oxford, Astrophysics, Keble Road, Oxford OX1 3RH, UK 8Max-Planck-Institut fur¨ extraterrestrische Physik, 85748 Garching, Germany Accepted 2017 April 27. Received 2017 April 27; in original form 2017 January 12 ABSTRACT We present a low-frequency view of the Perseus cluster with new observations from the Karl G. Jansky Very Large Array (JVLA) at 230-470 MHz. The data reveal a multitude of new structures associated with the mini-halo. The mini-halo seems to be influenced both by the AGN activity as well as by the sloshing motion of the cool core cluster's gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. We present a detailed description of the data reduction and imaging process of the dataset. The depth and resolution of the observations allow us to conduct for the first time a detailed comparison of the mini-halo structure with the X-ray structure as seen in the Chandra X-ray images. The resulting image shows very clearly that the mini-halo emission is mostly contained behind the western cold front, similar to that predicted by simulations of gas sloshing in galaxy clusters, but fainter emission is also seen beyond, as if particles are leaking out. However, due to the proximity of the Perseus cluster, as well as the quality of the data at low radio frequencies and at X-ray wavelengths, we also find evidence of fine structure. This structure includes several radial radio filaments extending in different directions, a concave radio structure associated with the southern X-ray bay and sharp radio edges that correlate with X-ray edges. Mini-halos are therefore not simply diffuse, uniform radio sources, but rather have a rich variety of complex structures. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies, as well as the necessity to obtain deeper, higher-fidelity radio images of mini-halos in clusters to further understand their origin. Key words: Galaxies: clusters: individual: Perseus cluster - galaxies: jets - radio continuum: galaxies - X-rays: galaxies: clusters - cooling flows arXiv:1701.03791v2 [astro-ph.CO] 13 Jun 2017 1 INTRODUCTION anism consists of relativistic jets powered by accretion onto the supermassive black hole (SMBH) that inflate bubbles, Radio mode feedback in clusters of galaxies is the process by displacing the ICM and creating regions of depleted X-ray which the energy released by the central active galactic nu- emission. These bubbles, filled with relativistic plasma (i.e., clei (AGN) is injected into the intracluster medium (ICM) radio lobes), are often discernible at ∼ GHz frequencies. through turbulence, shocks or sound waves, compensating its radiative losses (e.g. B^ırzan et al. 2004; Dunn & Fabian The Perseus cluster, the brightest cluster in the X-ray 2006; Rafferty et al. 2006). The energy source of this mech- sky, was one of the first examples in which such radio mode feedback was observed. However, in addition to finding two inner cavities filled with radio emission at 5 < r < 20 kpc ? E-mail: [email protected] from the AGN (B¨ohringer et al. 1993), another pair of outer c 2017 The Authors 2 M. Gendron-Marsolais et al. 18’= 400 kpc Beam 59:59.9 NGC 1265 47:59.9 NGC 1275 35:59.9 CR 15 IC 310 41:23:59.9 11:59.9 23:12.0 22:24.0 21:36.0 48.0 3:20:00.0 19:12.0 18:24.0 17:36.0 48.0 16:00.0 40:59:59.9 Figure 1. The central 2 ◦ ×1:5 ◦ of the total field of view of the JVLA 230-470 MHz radio map obtained in B-configuration. NGC 1275 is the bright source in the middle of the image. Tow wide-angle tail radio galaxies, NGC 1265 (NNW of NGC 1275) and CR 15 (between NGC 1275 and IC 310) as well as IC 310 (WSW of NGC 1275) are clearly visible. The resulting image has a rms noise of 0.35 mJy/beam, a beam size of 22:100 × 11:300 and a peak of 10.63 Jy/beam. cavities was identified further out at 25 < r < 45 kpc and de- waves in the Perseus cluster (Fabian et al. 2003), as well as void of high-frequency radio emission (Branduardi-Raymont shocks around cavities (Fabian et al. 2006), a semicircular et al. 1981; Fabian et al. 1981; Churazov et al. 2000). These cold front, two new elliptical cavities interpreted as potential were interpreted as \ghost" cavities, inflated in the past by ghost bubbles, two large regions of weak X-ray luminosity the jets of the central SMBH and now rising buoyantly as a (the northern trough and the southern bay) and a loop-like gas bubble does in a liquid. As the population of particles structure above a long Ha filament (Fabian et al. 2011). filling cavities loses its energy through synchrotron emission, the radio lobes become less clear at higher radio frequencies, The Perseus cluster also harbours a mini-halo (Sobol- providing an explanation of the lack of high-frequency radio eva et al. 1983; Pedlar et al. 1990; Burns et al. 1992; Sijbring emission in the older ghost cavities (e.g. Blundell et al. 2002; 1993), a faint diffuse source of radio emission detected so far Fabian et al. 2002). in about thirty cool core clusters (Giacintucci et al. 2017, see Feretti et al. 2012 for a review). The X-rays and mini-halo Heinz et al.(1998) first estimated the input power of structure of Perseus have been compared in Fabian et al. the jets originating from the AGN in the central dominant (2011). This emission differs from that filling the X-ray cav- galaxy NGC 1275, known as the Brightest Cluster Galaxy ities, being 3 times radio fainter and having a steeper spec- (BCG, Forman et al. 1972), to be of the order of 1045 erg s−1, & tral index (a < −1 for S(n) ∝ na , where S is the flux den- a value comparable to the radiative losses. This AGN is sity and n is the frequency, Giacintucci et al. 2014a). Since +7 8 thought to be powered by a 8−2 × 10 M SMBH (Schar- the radiative timescale of the electrons is much shorter than w¨achter et al. 2013). The advent of the Chandra X-ray ob- the time required for them to reach the extent of the mini- servatory and its high spatial resolution enabled, in addition, halo, the origin of mini-halos remains unclear. Two possible the detection of quasi-spherical ripples interpreted as sound mechanisms have been proposed in the literature to explain MNRAS 000,1{9 (2017) The mini-halo in the Perseus Cluster at 230-470 MHz 3 the mini-halo emission: it might originate from the reaccel- eration of pre-existing electrons by turbulence (Gitti et al. 4’= 90 kpc 2002, 2004) or from the generation of new particles from in- Beam elastic collisions between relativistic cosmic-ray protons and Northern extension thermal protons (e.g. Pfrommer & Enßlin 2004). Simulations seem to suggest that turbulence created by sloshing motions of the cold gas in the core region is sufficient to re-accelerate Eastern spurs electrons (e.g. ZuHone et al. 2013). A key prediction of these simulations is that mini-halos should be bounded by cold NGC 1272 fronts. Observationally, the Hitomi Soft X-ray Spectrometer showed that the line-of-sight velocity dispersions are on the order of 164 ± 10 km/s in the 30-60 kpc region around the nucleus of the Perseus cluster. This is sufficient to sustain the synchrotron emission of relativistic electrons population (Hitomi collaboration 2016) and sets a limit on the maxi- mum energy density in turbulent motions available (Fabian South-western et al. 2017). The efficiency of the acceleration by turbulence edge depends however on the assumptions on the spectrum of Southern edge Plume turbulent motions and on the ICM microphysics (Brunetti 2016). In this article, we present new, deep Karl G. Jansky Figure 2. A zoom on the emission surrounding NGC 1275 from Very Large Array (JVLA) observations of the Perseus clus- the 270-430 MHz radio map seen in Fig.1. The main structures ter in the P-band (230-470 MHz). The resolution and sensi- of the mini-halo are identified: the northern extension, the two tivity of these data provide a detailed and extended view of eastern spurs, the concave edge to the south, the south-western the mini-halo structure, on which we will focus our analysis. edge and a plume of emission to the south-south-west. The small The recent update of the facilities with the EVLA project knob at the end of the western tail is the galaxy NGC 1272.