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1. SPT-CL J2215−3537: A Massive Starburst at the Center of the Most Distant Relaxed Galaxy Cluster

   https://doi.org/10.3847/1538-4357/acc6c2  

   Calzadilla, Michael S. ; Bleem, Lindsey E. ; McDonald, Michael ; Gladders, Michael D. ; Mantz, Adam B. ; Allen, Steven W. ; Bayliss, Matthew B. ; Eilers, Anna-Christina ; Floyd, Benjamin ; Hlavacek-Larrondo, Julie ; et al ( April 2023 , The Astrophysical Journal)

   We present the discovery of the most distant, dynamically relaxed cool core cluster, SPT-CL J2215−3537 (SPT2215), and its central brightest cluster galaxy (BCG) atz= 1.16. Using new X-ray observations, we demonstrate that SPT2215 harbors a strong cool core with a central cooling time of 200 Myr (at 10 kpc) and a maximal intracluster medium cooling rate of 1900 ± 400M_⊙yr⁻¹. This prodigious cooling may be responsible for fueling the extended, star-forming filaments observed in Hubble Space Telescope imaging. Based on new spectrophotometric data, we detect bright [Oii] emission in the BCG, implying an unobscured star formation rate (SFR) of${320}_{-140}^{+230}$M_⊙yr⁻¹. The detection of a weak radio source (2.0 ± 0.8 mJy at 0.8 GHz) suggests ongoing feedback from an active galactic nucleus (AGN), though the implied jet power is less than half the cooling luminosity of the hot gas, consistent with cooling overpowering heating. The extreme cooling and SFR of SPT2215 are rare among known cool core clusters, and it is even more remarkable that we observe these at such high redshift, when most clusters are still dynamically disturbed. The high mass of this cluster, coupled with the fact that it is dynamically relaxed with a highly isolated BCG, suggests that it is an exceptionally rare system that must have formed very rapidly in the early universe. Combined with the high SFR, SPT2215 may be a high-zanalog of the Phoenix cluster, potentially providing insight into the limits of AGN feedback and star formation in the most massive galaxies.

    

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2. The Abell 3391/95 galaxy cluster system: A 15 Mpc intergalactic medium emission filament, a warm gas bridge, infalling matter clumps, and (re-) accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU and DECam data

   https://doi.org/10.1051/0004-6361/202039590  

   Reiprich, T. H. ; Veronica, A. ; Pacaud, F. ; Ramos-Ceja, M. E. ; Ota, N. ; Sanders, J. ; Kara, M. ; Erben, T. ; Klein, M. ; Erler, J. ; et al ( March 2021 , Astronomy & Astrophysics)

   null (Ed.)

   Context. Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters. Aims. Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model. Methods. We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg 2 region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the Planck survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite. Results. We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii, r 200 . Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius, r 100 , of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift z = 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at >4 σ . The Planck SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the individual system level, including the surrounding warm-hot intergalactic medium distribution; the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure. 

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3. Constraining radio mode feedback in galaxy clusters with the cluster radio AGNs properties to z ∼ 1

   https://doi.org/10.1093/mnras/staa832  

   Gupta, N ; Pannella, M ; Mohr, J J ; Klein, M ; Rykoff, E S ; Annis, J ; Avila, S ; Bianchini, F ; Brooks, D ; Buckley-Geer, E ; et al ( May 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We study the properties of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz radio active galactic nuclei (AGNs) population in galaxy clusters from two large catalogues created using the Dark Energy Survey (DES): ∼11 800 optically selected RM-Y3 and ∼1000 X-ray selected MARD-Y3 clusters. We show that cluster radio loud AGNs are highly concentrated around cluster centres to $z$ ∼ 1. We measure the halo occupation number for cluster radio AGNs above a threshold luminosity, finding that the number of radio AGNs per cluster increases with cluster halo mass as N ∝ M1.2 ± 0.1 (N ∝ M0.68 ± 0.34) for the RM-Y3 (MARD-Y3) sample. Together, these results indicate that radio mode feedback is favoured in more massive galaxy clusters. Using optical counterparts for these sources, we demonstrate weak redshift evolution in the host broad-band colours and the radio luminosity at fixed host galaxy stellar mass. We use the redshift evolution in radio luminosity to break the degeneracy between density and luminosity evolution scenarios in the redshift trend of the radio AGNs luminosity function (LF). The LF exhibits a redshift trend of the form (1 + $z$)γ in density and luminosity, respectively, of γD = 3.0 ± 0.4 and γP = 0.21 ± 0.15 in the RM-Y3 sample, and γD = 2.6 ± 0.7 and γP = 0.31 ± 0.15 in MARD-Y3. We discuss the physical drivers of radio mode feedback in cluster AGNs, and we use the cluster radio galaxy LF to estimate the average radio-mode feedback energy as a function of cluster mass and redshift and compare it to the core (<0.1R500) X-ray radiative losses for clusters at $z$ < 1. 

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4. 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 with 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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5. RASS-MCMF: a full-sky X-ray selected galaxy cluster catalogue

   https://doi.org/10.1093/mnras/stad2729  

   Klein, Matthias ; Hernández-Lang, Daniel ; Mohr, Joseph J. ; Bocquet, Sebastian ; Singh, Aditya ( September 2023 , Monthly Notices of the Royal Astronomical Society)

   We present the RASS-MCMF catalogue of 8449 X-ray selected galaxy clusters over 25 000 deg2 of extragalactic sky. The accumulation of deep multiband optical imaging data, the development of the Multi-Component Matched Filter (MCMF) cluster confirmation algorithm, and the release of the DESI Legacy Survey DR10 catalogue makes it possible – for the first time, more than 30 yr after the launch of the ROSAT X-ray satellite – to identify the majority of the galaxy clusters detected in the second ROSAT All-Sky-Survey (RASS) source catalogue (2RXS). The resulting 90 per cent pure RASS-MCMF catalogue is the largest intracluster medium (ICM)-selected cluster sample to date. RASS-MCMF probes a large dynamic range in cluster mass spanning from galaxy groups to the most massive clusters. The cluster redshift distribution peaks at $z$ ∼ 0.1 and extends to redshifts $z$ ∼ 1. Out to $z$ ∼ 0.4, the RASS-MCMF sample contains more clusters per redshift interval (dN/dz) than any other ICM-selected sample. In addition to the main sample, we present two subsamples with 6912 and 5506 clusters, exhibiting 95 per cent and 99 per cent purity, respectively. We forecast the utility of the sample for a cluster cosmological study, using realistic mock catalogues that incorporate most observational effects, including the X-ray exposure time and background variations, the existence likelihood selection and the impact of the optical cleaning with the algorithm MCMF. Using realistic priors on the observable–mass relation parameters from a DES-based weak lensing analysis, we estimate the constraining power of the RASS-MCMF×DES sample to be of 0.026, 0.033, and 0.15 (1σ) on the parameters Ωm, σ8, and $w$, respectively.

    

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