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1. Evidence for AGN-regulated Cooling in Clusters at z ∼ 1.4: A Multiwavelength View of SPT-CL J0607-4448

   https://doi.org/10.3847/1538-4357/acae9e  

   Masterson, Megan ; McDonald, Michael ; Ansarinejad, Behzad ; Bayliss, Matthew ; Benson, Bradford A. ; Bleem, Lindsey E. ; Calzadilla, Michael S. ; Edge, Alastair C. ; Floyd, Benjamin ; Kim, Keunho J. ; et al ( February 2023 , The Astrophysical Journal)

   We present a multiwavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope atz= 1.4010 ± 0.0028. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool-core nature of the cluster is supported by a centrally peaked density profile and low central entropy ($K_0={18}_{-9}^{+11}$keV cm²), which we estimate assuming an isothermal temperature profile due to the limited spectral information given the distance to the cluster. Using the density profile and gas cooling time inferred from the X-ray data, we find a mass-cooling rate${\dot{M}}_{\mathrm{cool}}={100}_{-60}^{+90}{M}_{\odot }$yr⁻¹. From optical spectroscopy and photometry around the [Oii] emission line, we estimate that the BCG star formation rate is${\mathrm{SFR}}_{[\mathrm{O}\mathrm{II}]}={1.7}_{-0.6}^{+1.0}{M}_{\odot }$yr⁻¹, roughly two orders of magnitude lower than the predicted mass-cooling rate. In addition, using ATCA radio data at 2.1 GHz, we measure a radio jet power$P_{\mathrm{cav}}={3.2}_{-1.3}^{+2.1}\times {10}^{44}$erg s⁻¹, which is consistent withmore »the X-ray cooling luminosity ($L_{\mathrm{cool}}={1.9}_{-0.5}^{+0.2}\times {10}^{44}$erg s⁻¹withinr_cool= 43 kpc). These findings suggest that SPT0607 is a relaxed, cool-core cluster with AGN-regulated cooling at an epoch shortly after cluster formation, implying that the balance between cooling and feedback can be reached quickly. We discuss the implications for these findings on the evolution of AGN feedback in galaxy clusters.

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2. AGN feeding and feedback in M84: from kiloparsec scales to the Bondi radius

   https://doi.org/10.1093/mnras/stad824  

   Bambic, C. J. ; Russell, H. R. ; Reynolds, C. S. ; Fabian, A. C. ; McNamara, B. R. ; Nulsen, P. E. J. ( May 2023 , Monthly Notices of the Royal Astronomical Society)

   We present the deepest Chandra observation to date of the galaxy M84 in the Virgo Cluster, with over 840 ks of data provided by legacy observations and a recent 730 ks campaign. The increased signal-to-noise ratio allows us to study the origins of the accretion flow feeding the supermassive black hole in the centre of M84 from the kiloparsec scales of the X-ray halo to the Bondi radius, RB. Temperature, metallicity, and deprojected density profiles are obtained in four sectors about M84’s active galactic nucleus (AGN), extending into the Bondi radius. Rather than being dictated by the potential of the black hole, the accretion flow is strongly influenced by the AGN’s bipolar radio jets. Along the jet axis, the density profile is consistent with ne ∝ r−1; however, the profiles flatten perpendicular to the jet. Radio jets produce a significant asymmetry in the flow, violating a key assumption of Bondi accretion. Temperature in the inner kiloparsec is approximately constant, with only a slight increase from 0.6 to 0.7 keV approaching RB, and there is no evidence for a temperature rise imposed by the black hole. The Bondi accretion rate $\dot{M}_{\rm B}$ exceeds the rate inferred from AGN luminosity and jet power bymore »over four orders of magnitude. In sectors perpendicular to the jet, $\dot{M}_{\rm B}$ measurements agree; however, the accretion rate is >4σ lower in the North sector along the jet, likely due to cavities in the X-ray gas. Our measurements provide unique insight into the fuelling of AGN responsible for radio mode feedback in galaxy clusters.

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3. Chandra view of Abell 407: the central compact group of galaxies and the interaction between the radio AGN and the ICM

   https://doi.org/10.1093/mnras/stac355  

   Geng, Chao ; Ge, Chong ; Lal, Dharam V. ; Sun, Ming ; Ji, Li ; Xu, Haiguang ; Liu, Wenhao ; Hardcastle, Martin ; Forman, William ; Kraft, Ralph ; et al ( February 2022 , Monthly Notices of the Royal Astronomical Society)

   Abell 407 (A407) is a unique galaxy cluster hosting a central compact group of nine galaxies (named as ‘Zwicky’s Nonet’; G1–G9 in this work) within a 30 kpc radius region. The cluster core also hosts a luminous radio active galactic nucleus (AGN), 4C 35.06 with helically twisted jets extending over 200 kpc. With a 44 ks Chandra observation of A407, we characterize the X-ray properties of its intracluster medium and central galaxies. The mean X-ray temperature of A407 is 2.7 keV and the M200 is $1.9 \times 10^{14}\, {\mathrm{M}_{\odot }}$. We suggest that A407 has a weak cool core at r < 60 kpc scales and at its very centre, <1–2 kpc radius, a small galaxy corona associated with the strong radio AGN. We also conclude that the AGN 4C 35.06 host galaxy is most likely G3. We suggest that the central group of galaxies is undergoing a ‘slow merge’ procedure. The range of the merging time-scale is 0.3 ∼ 2.3 Gyr and the stellar mass of the future brightest cluster galaxy (BCG) will be $7.4\times 10^{11} \, \mathrm{M}_{\odot }$. We find that the regions that overlap with the radio jets have higher temperature and metallicity. This is consistent with AGN feedback activity. The central entropy ismore »higher than that for other clusters, which may be due to the AGN feedback and/or merging activity. With all these facts, we suggest that A407 is a unique and rare system in the local universe that could help us to understand the formation of a massive BCG.

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4. The contribution of non-central radio galaxies to AGN feedback in rich galaxy clusters

   https://doi.org/10.1093/mnras/stac1064  

   Seth, Ruchika ; O’Sullivan, Ewan ; Sebastian, Biny ; Raychaudhury, Somak ; Schellenberger, Gerrit ; Haines, Christopher P. ( April 2022 , Monthly Notices of the Royal Astronomical Society)

   We present a combined radio/X-ray study of six massive galaxy clusters, aimed at determining the potential for heating of the intra-cluster medium (ICM) by non-central radio galaxies. Since X-ray cavities associated with the radio lobes of non-central galaxies are generally not detectable, we use Giant Metrewave Radio Telescope 610 MHz observations to identify jet sources and estimate their size, and Chandra data to estimate the pressure of the surrounding ICM. In the radio, we detect 4.5 per cent of galaxies above the spectroscopic survey limit (M$^{*}_{K}$ + 2.0) of the Arizona cluster redshift survey (ACReS) that covers five of our six clusters. Approximately one-tenth of these are extended radio sources. Using star formation (SF) rates determined from mid-infrared data, we estimate the expected contribution to radio luminosity from the stellar population of each galaxy, and find that most of the unresolved or poorly resolved radio sources are likely SF dominated. The relatively low frequency and good spatial resolution of our radio data allows us to trace SF emission down to galaxies of stellar mass ∼10 9.5 M⊙. We estimate the enthalpy of the (AGN-dominated) jet/lobe and tailed sources, and place limits on the energy available from unresolved radio jets. We find jet powers inmore »the range ∼1043 to 1046 erg s−1, comparable to those of brightest cluster galaxies. Our results suggest that while cluster-central sources are the dominant factor balancing ICM cooling over the long-term, non-central sources may have a significant impact, and that further investigation is possible and warranted.

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5. An H α/X-ray orphan cloud as a signpost of intracluster medium clumping

   https://doi.org/10.1093/mnras/stab1569  

   Ge, Chong ; Luo, Rongxin ; Sun, Ming ; Yagi, Masafumi ; Jáchym, Pavel ; Boselli, Alessandro ; Fossati, Matteo ; Nulsen, Paul E ; Sarazin, Craig ; Edge, Tim ; et al ( June 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Recent studies have highlighted the potential significance of intracluster medium (ICM) clumping and its important implications for cluster cosmology and baryon physics. Many of the ICM clumps can originate from infalling galaxies, as stripped interstellar medium (ISM) mixing into the hot ICM. However, a direct connection between ICM clumping and stripped ISM has not been unambiguously established before. Here, we present the discovery of the first and still the only known isolated cloud (or orphan cloud [OC]) detected in both X-rays and H α in the nearby cluster A1367. With an effective radius of 30 kpc, this cloud has an average X-ray temperature of 1.6 keV, a bolometric X-ray luminosity of ∼3.1 × 1041 erg s−1, and a hot gas mass of ∼1010 M⊙. From the Multi-Unit Spectroscopic Explorer (MUSE) data, the OC shows an interesting velocity gradient nearly along the east-west direction with a low level of velocity dispersion of ∼80 km s−1, which may suggest a low level of the ICM turbulence. The emission line diagnostics suggest little star formation in the main H α cloud and a low-ionization (nuclear) emission-line regions like spectrum, but the excitation mechanisms remain unclear. This example shows that stripped ISM, even long after the initial removal from the galaxy, can still inducemore »ICM inhomogeneities. We suggest that the magnetic field can stabilize the OC by suppressing hydrodynamic instabilities and thermal conduction. This example also suggests that at least some ICM clumps are multiphase in nature and implies that the ICM clumps can also be traced in H α. Thus, future deep and wide-field H α surveys can be used to probe the ICM clumping and turbulence.« less