A complete view of the outskirts of the Coma cluster

Abstract

We present a new extended XMM-Newton mosaic of the nearby Coma cluster, which covers the cluster out to the virial radius with nearly complete azimuthal coverage. This large mosaic is combined with the Planck Sunyaev Zel’dovich effect observations to recover the thermodynamic properties of the intracluster medium in an azimuthally averaged profile and 36 angular sectors, producing the highest spatial resolution view of the thermodynamics of the outskirts of a galaxy cluster in its entirety. Beyond r500, our clumping corrected entropy measurements along the less disturbed directions are statistically consistent with the power-law entropy profile predicted by non-radiative simulations, and the gas mass fraction agrees with the mean cosmic baryon fraction. However, there is a clear entropy deficit in the outskirts to the southwest, coinciding with where Coma connects to a cosmic web filament which joins it to Abell 1367. The low entropy to the southwest extends from 0.5-1.0r200, and is consistent with what is expected from simulations of a filamentary gas stream penetrating into the cluster as it continues to accrete matter from the cosmic web. We also find that the radial profiles of the recovered quantities become increasingly asymmetric in the outskirts, particularly along the more disturbed directions, consistent with the predictions of cosmological simulations.

γ-ray detection toward the Coma cluster withFermi-LAT: Implications for the cosmic ray content in the hadronic scenario

“…It also coincides well with the location where a radio front was identified (Brown & Rudnick 2011). This front is coincident with a discontinuity seen in the X-ray surface brightness, temperature and entropy (Simionescu et al 2013;Uchida et al 2016;Mirakhor & Walker 2020) local CR might have been accelerated by a shock. However, given the significance of the excess and the Fermi-LAT angular resolution, this remains difficult to interpret further, as also shown in Sect.…”

“…The region around Coma is not affected by the presence of bright γray compact sources. Finally, the Coma cluster is a well-known ongoing merger, which has been extensively observed at various wavelengths using various probes (e.g., Kent & Gunn 1982;Briel et al 1992;Gavazzi et al 2009;Bonafede et al 2010;Planck Collaboration X 2013;Mirakhor & Walker 2020). In particular, a well-measured giant radio halo and a radio relic have been observed, proving the presence of CRe (e.g., Willson 1970;Giovannini et al 1993;Thierbach et al 2003;Brown & Rudnick 2011;Bonafede et al 2021).…”

Tempestuous life beyond R500: X-ray view on the Coma cluster with SRG/eROSITA

“…This image reveals some of the features, which appear less prominently in the original image. Some of these features have already been noticed in the ROSAT, XMM-Newton and Chandra images (e.g., Vikhlinin et al 1997;Donnelly et al 1999;Watanabe et al 1999;Neumann et al 2003;Sanders et al 2013;Simionescu et al 2013;Mirakhor & Walker 2020), although in the flattened eROSITA image these features can now be traced over their full extent 2 . The most spectacular is a bow-like sharp 1 Formally the singly scattered photons should be removed from the observed profile before the convolution.…”

“…Due to different dependences of the X-ray and SZ signals on the gas density and temperature, it is possible to use them in order A41, page 5 of 16 A&A 651, A41 (2021) to constrain the gas thermodynamic properties or variations of these properties (see, e.g., Ghirardini et al 2018;Churazov et al 2016). In particular, Mirakhor & Walker (2020) combined the XMM-Newton and Planck data on the Coma cluster in a number of wedges. With the extended spatial coverage provided by eROSITA, it is now possible to further advance the joint analysis of the SZ and X-ray data.…”

“…While initially classified as a relaxed cluster (e.g., Kent & Gunn 1982), it later became recognized as a merger (e.g., Fitchett & Webster 1987;Briel et al 1992;Neumann et al 2003). Recent studies of the Coma cluster in X-rays revealed a number of substructures, which are plausibly connected to the recent merger(s), namely, a prominent X-ray excess to the west of the Coma center (Neumann et al 2003;Simionescu et al 2013), an excess to the east, elongated in the east-west direction (Vikhlinin et al 1997;Neumann et al 2003;Simionescu et al 2013), the NGC 4839 group merging with Coma (e.g., Burns et al 1994;Neumann et al 2001;Lyskova et al 2019;Malavasi et al 2020;Mirakhor & Walker 2020), and high density "arms" in the Coma core (Churazov et al 2012;Sanders et al 2013Sanders et al , 2020Zhuravleva et al 2019). Similarly, remarkable progress with characterizing the Coma cluster has been achieved in the optical and radio bands (Adami et al 2005;Malavasi et al 2020;Brown & Rudnick 2011;Bonafede et al 2021, among others).…”