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1. A Rapidly Accreting Active Galactic Nucleus Hidden in a Dust-obscured Galaxy at z ∼ 0.8

   https://doi.org/10.3847/1538-4357/ad8c3f  

   Cristello, Nathan; Zou, Fan; Brandt, William_N; Yu, Zhibo; Vito, Fabio; Zhu, Shifu (December 2024, The Astrophysical Journal)

   Abstract Dust-obscured galaxies (DOGs) containing central supermassive black holes (SMBHs) that are rapidly accreting (i.e., having high Eddington ratios,λ_Edd) may represent a key phase closest to the peak of both the black hole and galaxy growth in the coevolution framework for SMBHs and galaxies. In this work, we present a 68 ks XMM-Newton observation of the high-λ_EddDOG J1324+4501 atz∼ 0.8, which was initially observed by Chandra. We analyze the XMM-Newton spectra jointly with archival Chandra spectra. In performing a detailed X-ray spectral analysis, we find that the source is intrinsically X-ray luminous with $\log (L_{\mathrm{X}}$/erg ${\mathrm{s}}^{-1})={44.71}_{-0.12}^{+0.08}$and heavily obscured with $\log \left(N_{\mathrm{H}}/{\mathrm{cm}}^{-2}\right)={23.43}_{-0.13}^{+0.09}$. We further utilize UV-to-IR archival photometry to measure and fit the source’s spectral energy distribution to estimate its host-galaxy properties. We present a supplementary comparison sample of 21 X-ray luminous DOGs from the XMM-SERVS survey with sufficient (>200) 0.5–10 keV counts to perform a similarly detailed X-ray spectral analysis. Of the X-ray luminous DOGs in our sample, we find that J1324+4501 is the most remarkable, possessing one of the highest X-ray luminosities, column densities, and star formation rates. We demonstrate that J1324+4501 is in an extreme evolutionary stage where SMBH accretion and galaxy growth are at their peaks. 

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2. Investigating the Star Formation Rates of Active Galactic Nucleus Hosts Relative to the Star-forming Main Sequence

   https://doi.org/10.3847/1538-4357/ad2177  

   Cristello, Nathan; Zou, Fan; Brandt, W. N.; Chen, Chien-Ting J.; Leja, Joel; Ni, Qingling; Yang, Guang (February 2024, The Astrophysical Journal)

   Abstract A fundamental question in galaxy and black hole evolution remains how galaxies and their supermassive black holes have evolved together over cosmic time. Specifically, it is still unclear how the position of X-ray active galactic nucleus (AGN) host galaxies with respect to the star-forming main sequence (MS) may change with the X-ray luminosity (L_X) of the AGN or the stellar mass (M_⋆) of the host galaxy. We use data from the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) to probe this issue. XMM-SERVS is covered by the largest medium-depth X-ray survey (with superb supporting multiwavelength data) and thus contains the largest sample to date for study. To ensure consistency, we locally derive the MS from a large reference galaxy sample. In our analysis, we demonstrate that the turnover of the galaxy MS does not allow reliable conclusions to be drawn for high-mass AGNs, and we establish a robust safe regime where the results do not depend upon the choice of MS definition. Under this framework, our results indicate that less massive AGN host galaxies ( $\log M_{\star }\sim 9.5–10.5M_{\odot }$) generally possess enhanced star formation rates compared to their normal-galaxy counterparts while the more massive AGN host galaxies ( $\log M_{\star }\sim 10.5–11.5M_{\odot }$) lie on or below the star-forming MS. Further, we propose an empirical model for how the placement of an AGN with respect to the MS (SFR_norm) evolves as a function of bothM_⋆andL_X. 

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3. The X-Ray Link between High Eddington Ratio Dust-obscured Galaxies (DOGs) and Hot DOGs

   https://doi.org/10.3847/1538-4357/adf55c  

   Zou, Fan; Brandt, W N; Gallo, Elena; Vito, Fabio; Yu, Zhibo (September 2025, The Astrophysical Journal)

   Abstract Dust-obscured galaxies (DOGs) with extremely red optical-to-infrared colors are often associated with intense starburst and active galactic nucleus (AGN) activity. Studying DOGs can provide insights into the processes that drive the growth of galaxies and their central supermassive black holes. However, the general DOG population is heterogeneous, spanning a wide range of evolutionary stages, and has X-ray obscuring column densities (N_H) covering low to high levels. In this work, we focus on seven high Eddington ratio DOGs ( $\log {\lambda }_{\mathrm{Edd}}\gtrsim -0.5$) to examine their X-ray obscuration properties using new and archival X-ray observations. We confirm that these systems are generally heavily obscured, with six out of seven havingN_H ≳ 10²³cm⁻²and three out of seven havingN_H ≳ 10²⁴cm⁻². Based on the observed similarity with the rare Hot DOG population, we argue that both high-λ_EddDOGs and Hot DOGs likely trace the postmerger phase, during which AGNs are enshrouded by large columns of dust-rich material. 

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4. Dinosaur in a Haystack: X-Ray View of the Entrails of SN 2023ixf and the Radio Afterglow of Its Interaction with the Medium Spawned by the Progenitor Star (Paper I)*

   https://doi.org/10.3847/1538-4357/adc2fb  

   A_J, Nayana; Margutti, Raffaella; Wiston, Eli; Chornock, Ryan; Campana, Sergio; Laskar, Tanmoy; Murase, Kohta; Krips, Melanie; Migliori, Giulia; Tsuna, Daichi; et al (May 2025, The Astrophysical Journal)

   Abstract We present the results from our extensive hard-to-soft X-ray (NuSTAR, Swift-XRT, XMM-Newton, Chandra) and meter-to-millimeter-wave radio (Giant Metrewave Radio Telescope, Very Large Array, NOEMA) monitoring campaign of the very nearby (d = 6.9 Mpc) Type II supernova (SN) 2023ixf spanning ≈4–165 days post-explosion. This unprecedented data set enables inferences on the explosion’s circumstellar medium (CSM) density and geometry. In particular, we find that the luminous X-ray emission is well modeled by thermal free–free radiation from the forward shock with rapidly decreasing photoelectric absorption with time. The radio spectrum is dominated by synchrotron radiation from the same shock. Similar to the X-rays, the level of free–free absorption affecting the radio spectrum rapidly decreases with time as a consequence of the shock propagation into the dense CSM. While the X-ray and the radio modeling independently support the presence of a dense medium corresponding to an effective mass-loss rate $\dot{M}\approx 10^{-4}{M}_{\odot }{\mathrm{yr}}^{-1}$atR = (0.4–14) × 10¹⁵cm (forv_w = 25 km s⁻¹), our study points at a complex CSM density structure with asymmetries and clumps. The inferred densities are ≈10–100 times those of typical red supergiants, indicating an extreme mass-loss phase of the progenitor in the ≈200 yr preceding core collapse, which leads to the most X-ray luminous Type II SN and the one with the most delayed emergence of radio emission. These results add to the picture of the complex mass-loss history of massive stars on the verge of collapse and demonstrate the need for panchromatic campaigns to fully map their intricate environments. 

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5. 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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