High-Resolution VLA Low Radio Frequency Observations of the Perseus Cluster: Radio Lobes, Mini-Halo and Bent-Jet Radio Galaxies
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MNRAS 000,1{17 (2020) Preprint 12 November 2020 Compiled using MNRAS LATEX style file v3.0 High-resolution VLA low radio frequency observations of the Perseus cluster: radio lobes, mini-halo and bent-jet radio galaxies M. Gendron-Marsolais1?, J. Hlavacek-Larrondo2, R. J. van Weeren3, L. Rudnick4, T. E. Clarke5, B. Sebastian6, T. Mroczkowski7, A. C. Fabian8, K. M. Blundell9, E. Sheldahl10, K. Nyland11, J. S. Sanders12, W. M. Peters5, and H. T. Intema3 1European Southern Observatory, Alonso de Co´ordova 3107, Vitacura, Casilla 19001, Santiago de Chile 2D´epartement de Physique, Universit´ede Montr´eal, Montr´eal, QC H3C 3J7, Canada 3Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333CA, Leiden, The Netherlands 4Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA 5Naval Research Laboratory, Code 7213, 4555 Overlook Ave. SW, Washington, DC 20375, USA 6National Center for Radio Astrophysics - Tata Institute of Fundamental Research Post Box 3, Ganeshkhind P.O., Pune 41007, India 7European Southern Observatory, Karl-Schwarzschild-Str. 2, DE-85748 Garching b. Munchen,¨ Germany 8Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA 9University of Oxford, Astrophysics, Keble Road, Oxford OX1 3RH, UK 10University of New Mexico, Albuquerque, NM, USA 11 National Research Council, resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, USA 12Max-Planck-Institut fur¨ extraterrestrische Physik, 85748 Garching, Germany Accepted for publication in MNRAS ABSTRACT We present the first high-resolution 230-470 MHz map of the Perseus cluster obtained with the Karl G. Jansky Very Large Array. The high dynamic range and resolution achieved has allowed the identification of previously-unknown structures in this nearby galaxy cluster. New hints of sub-structures appear in the inner radio lobes of the brightest cluster galaxy NGC 1275. The spurs of radio emission extending into the outer X-ray cavities, inflated by past nuclear outbursts, are seen for the first time at these frequencies, consistent with spectral aging. Beyond NGC 1275, we also analyze complex radio sources harbored in the cluster. Two new distinct, narrowly-collimated jets are visible in IC 310, consistent with a highly-projected narrow-angle tail radio galaxy infalling into the cluster. We show how this is in agreement with its blazar-like behavior, implying that blazars and bent-jet radio galaxies are not mutually exclusive. We report the presence of filamentary structures across the entire tail of NGC 1265, including two new pairs of long filaments in the faintest bent extension of the tail. Such filaments have been seen in other cluster radio sources such as relics and radio lobes, indicating that there may be a fundamental connection between all these radio structures. We resolve the very narrow and straight tail of CR 15 without indication of double jets, so that the interpretation of such head-tail sources is yet unclear. Finally, we note that only the brightest western parts of the mini-halo remain, near NGC 1272 and its bent double jets. arXiv:2005.12298v2 [astro-ph.GA] 10 Nov 2020 Key words: Galaxies: clusters: individual: Perseus cluster - galaxies: jets - radio con- tinuum: galaxies - X-rays: galaxies: clusters - cooling flows 1 INTRODUCTION our universe. The X-ray emitting intracluster medium (ICM) can be perturbed both internally by the outburst of the ac- Cluster environments host numerous remarkable phenomena tive galactic nuclei (AGN) of the dominant galaxy and ex- as they form the largest gravitationally bound structures in ternally from interactions with other clusters, groups, and individual galaxies The Perseus cluster is a classic example of such an environment. Being the brightest cluster in the ? E-mail: [email protected] © 2020 The Authors 2 M. Gendron-Marsolais et al. X-ray sky, it is a well-studied object and has been observed ies have bent radio jets caused by the ram pressure from the extensively across all the electromagnetic spectrum. ICM (e.g. Jones & Owen 1979; Begelman et al. 1979). Deep X-ray observations of the Perseus cluster have re- These multi-wavelength studies of the Perseus clus- vealed several types of disturbances in the ICM. At least two ter have fundamentally changed our understanding of clus- pairs of X-ray cavities have been identified: the first pair, ter's environment. Among these, the results presented in located at 5 < r < 20 kpc from the AGN, are filled with ra- Gendron-Marsolais et al.(2017) showed the capability of VLA data at 230-470 MHz to provide a detailed view of the dio emission (B¨ohringer et al. 1993) and the second, located further out at 25 < r < 45 kpc from the AGN, are devoid of radio structures in Perseus by revealing a multitude of new structures associated with the mini-halo. We now extend radio emission above & 1 GHz (Branduardi-Raymont et al. 1981; Fabian et al. 1981; Churazov et al. 2000). Inflated by this study to higher spatial resolutions and investigate the generations of outbursts from the central AGN, these con- smaller scales of the various radio structures at the same low stitute the imprint of radio mode feedback, injecting energy radio frequencies. In this article, we present new, deep VLA into the ICM and compensating its radiative losses. Beyond high-resolution observations of the Perseus cluster at 230- these cavities are ripple-like quasi-spherical structures inter- 470 MHz. These A-configuration observations reach a res- preted as sound waves which may be responsible for part olution more than 4 times higher than the B-configuration of the transport and dispersion of this energy throughout observations at the same frequencies presented in Gendron- the cooling region (Fabian et al. 2003). Shocks surrounding Marsolais et al.(2017) and constitute the highest resolution the inner cavities have also been identified in Fabian et al. observations of the Perseus cluster below 1 GHz. (2006). A large semicircular cold front is seen ∼ 100 kpc west In Section2, we present the observations used in this of the nucleus (Fabian et al. 2011), and another one is also work and the data reduction of the VLA dataset. Sections3, detected much further out, ∼ 730 kpc east of the nucleus 4,5 and6 discuss the different structures found in the radio (Simionescu et al. 2012; Walker et al. 2018). These struc- observations. Results are summarized in Section7. tures are interpreted as the result of perturbations of the We assume a redshift of z = 0:0183 for NGC 1275, the cluster's gravitational potential well from a minor merger. brightest cluster galaxy (BCG, Forman et al. 1972), corre- sponding to a luminosity distance of 78.4 Mpc, assuming Similar to cold fronts but with the opposite curvature, a −1 −1 H0 = 69:6 km s Mpc , WM = 0:286 and Wvac = 0:714. This large region of weak X-ray emission located ∼ 100 kpc south −1 of the nucleus has been identified as a \bay" (Fabian et al. corresponds to an angular scale of 22.5 kpc arcmin . 2011). It could be the imprint of a giant Kelvin-Helmholtz instability (Walker et al. 2017). Besides the radio emission directly originating from the 2 OBSERVATIONS AND DATA REDUCTION central AGN and its jets, a faint diffuse radio component is also present at lower frequencies (. 1GHz, Soboleva et al. 2.1 P-band (230-470 MHz) VLA observations 1983; Pedlar et al. 1990; Burns et al. 1992; Sijbring 1993), The Perseus cluster has been extensively imaged with the classified as a \mini-halo". Mini-halos are faint and diffuse pre-upgrade VLA at all frequencies and configurations. Here radio structures with steep spectra, filling the cooling core we present the first P-band (230-470 MHz) observations of of some relaxed clusters (e.g. Feretti et al. 2012; Giacintucci Perseus taken with the upgraded VLA (following the Ex- et al. 2017). Their origin remains unclear since the radiative panded Very Large Array Project, Perley et al. 2011) in timescale of the relativistic electrons coming from the cen- A-configuration (project 13B − 026, PI Hlavacek-Larrondo). tral AGN is much shorter than the time required for them to The data were taken on May 16, 2014 for a total of 5 hours. reach the extent of the mini-halo. Two possible mechanisms The A-configuration is the most extended of the VLA, yield- are debated to explain the mini-halo emission: the hadronic ing to the highest resolution, with typical synthesized beam or the turbulent re-acceleration models. According to these, sizes of ∼ 500 and maximum recoverable scales of ∼ 30 at P- mini-halos originate either from the generation of new par- band frequencies. We also obtained B-configuration obser- ticles from inelastic collisions between relativistic cosmic- vations (synthesized beam sizes of ∼ 1500 and largest recov- ray protons and thermal protons (e.g. Pfrommer & Enßlin erable scales of ∼ 100) that have been the subject of a recent 2004), or from the reacceleration of pre-existing electrons publication (see Gendron-Marsolais et al. 2017), focusing on by turbulence (Gitti et al. 2002, 2004). About thirty mini- the mini-halo emission. halos are known so far and most have irregular morpholo- The A-configuration observations were taken with 27 gies extending on ∼ 100 kpc scales (e.g. Giacintucci et al. operational antennas. Antenna 14 was flagged at the be- 2014a, 2017, 2019; Richard-Laferri`ere et al. 2020). Recent ginning of the data reduction process as problems with the deep NSF's Karl G. Jansky Very Large Array (VLA) ob- P-band receiver during the observation period were reported servations of the Perseus cluster at 230-470 MHz have how- in the operator log.