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1. 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)

   ABSTRACT 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 is 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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2. Redshift Evolution of the Feedback–Cooling Equilibrium in the Core of 48 SPT Galaxy Clusters: A Joint Chandra–SPT–ATCA Analysis

   https://doi.org/10.3847/1538-4357/acc38d  

   Ruppin, F.; McDonald, M.; Hlavacek-Larrondo, J.; Bayliss, M.; Bleem, L. E.; Calzadilla, M.; Edge, A. C.; Filipović, M. D.; Floyd, B.; Garmire, G.; et al (May 2023, The Astrophysical Journal)

   Abstract We analyze the cooling and feedback properties of 48 galaxy clusters at redshifts 0.4 < z < 1.3 selected from the South Pole Telescope (SPT) catalogs to evolve like the progenitors of massive and well-studied systems at z ∼ 0. We estimate the radio power at the brightest cluster galaxy (BCG) location of each cluster from an analysis of Australia Telescope Compact Array data. Assuming that the scaling relation between the radio power and active galactic nucleus (AGN) cavity power P cav observed at low redshift does not evolve with redshift, we use these measurements in order to estimate the expected AGN cavity power in the core of each system. We estimate the X-ray luminosity within the cooling radius L cool of each cluster from a joint analysis of the available Chandra X-ray and SPT Sunyaev–Zel’dovich (SZ) data. This allows us to characterize the redshift evolution of the P cav / L cool ratio. When combined with low-redshift results, these constraints enable investigations of the properties of the feedback–cooling cycle across 9 Gyr of cluster growth. We model the redshift evolution of this ratio measured for cool-core clusters by a log-normal distribution Log -  ( α + β z , σ 2 ) and constrain the slope of the mean evolution to β = −0.05 ± 0.47. This analysis improves the constraints on the slope of this relation by a factor of two. We find no evidence of redshift evolution of the feedback–cooling equilibrium in these clusters, which suggests that the onset of radio-mode feedback took place at an early stage of cluster formation. High values of P cav / L cool are found at the BCG location of noncool-core clusters, which might suggest that the timescales of the AGN feedback cycle and the cool core–noncool core transition are different. This work demonstrates that the joint analysis of radio, SZ, and X-ray data solidifies the investigation of AGN feedback at high redshifts. 

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3. 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)

   Abstract 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 ${\mathrm{SFR}}_{\left[\mathrm{O}\mathrm{II}\right]}={1.7}_{-0.6}^{+1.0}{M}_{\odot }$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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4. The composition and thermal properties of a cool core lacking a brightest cluster galaxy

   https://doi.org/10.1093/mnras/stad3172  

   Su, Yuanyuan; Combes, Francoise; Olivares, Valeria; Castignani, Gianluca; Torne, Pablo; van Weeren, Reinout (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present a multiwavelength observation of a cool core that does not appear to be associated with any galaxy, in a nearby cluster, Abell 1142. Its X-ray surface brightness peak of ≲2 keV is cooler than the ambient intracluster gas of ≳3 keV, and is offset from its brightest cluster galaxy (BCG) by 80 kpc in projection, representing the largest known cool core – BCG separation. This BCG-less cool core allows us to measure the metallicity of a cluster centre with a much-reduced contribution from the interstellar medium (ISM) of the BCG. XMM–Newton observation reveals a prominent Fe abundance peak of $$1.07^{+0.16}_{-0.15}$$ Z⊙ and an α/Fe abundance ratio close to the solar ratio, fully consistent with those found at the centres of typical cool core clusters. This finding hints that BCGs play a limited role in enriching the cluster centres. However, the discussion remains open, given that the α/Fe abundance ratios of the orphan cool core and the BCG ISM are not significantly different. Abell 1142 may have experienced a major merger more than 100 Myr ago, which has dissociated its cool core from the BCG. This implies that the Fe abundance peak in cool core clusters can be resilient to cluster mergers. Our recent Institut de Radio Astronomie Millimétrique 30-m observation did not detect any CO emission at its X-ray peak and we find no evidence for massive runaway cooling in the absence of recent active galactic nucleus feedback. The lack of a galaxy may contribute to an inefficient conversion of the ionized warm gas to the cold molecular gas. 

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5. Multiwavelength scrutiny of X-ray sources in dwarf galaxies: ULXs versus AGNs

   https://doi.org/10.1093/mnras/stad002  

   Thygesen, Erica; Plotkin, Richard M.; Soria, Roberto; Reines, Amy E.; Greene, Jenny E.; Anderson, Gemma E.; Baldassare, Vivienne F.; Owens, Milo G.; Urquhart, Ryan T.; Gallo, Elena; et al (January 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Owing to their quiet evolutionary histories, nearby dwarf galaxies (stellar masses $$M_\star \lesssim 3 \times 10^9 \, \mathrm{M}_\odot$$) have the potential to teach us about the mechanism(s) that ‘seeded’ the growth of supermassive black holes, and also how the first stellar mass black holes formed and interacted with their environments. Here, we present high spatial resolution observations of three dwarf galaxies in the X-ray (Chandra), the optical/near-infrared (Hubble Space Telescope), and the radio (Karl G. Jansky Very Large Array). These three galaxies were previously identified as hosting candidate active galactic nuclei on the basis of lower resolution X-ray imaging. With our new observations, we find that X-ray sources in two galaxies (SDSS J121326.01+543631.6 and SDSS J122111.29+173819.1) are off-nuclear and lack corresponding radio emission, implying they are likely luminous X-ray binaries. The third galaxy (Mrk 1434) contains two X-ray sources (each with LX ≈ 1040 erg s−1) separated by 2.8 arcsec, has a low metallicity [12 + log(O/H)  = 7.8], and emits nebular He ii λ4686 line emission. The northern source has spatially coincident point-like radio emission at 9.0 GHz and extended radio emission at 5.5 GHz. We discuss X-ray binary interpretations (where an ultraluminous X-ray source blows a ‘radio bubble’) and active galactic nucleus interpretations (where an $$\approx 4\times 10^5 \, \mathrm{M}_\odot$$ black hole launches a jet). In either case, we find that the He ii emission cannot be photoionized by the X-ray source, unless the source was ≈30–90 times more luminous several hundred years ago. 

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