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1. Now You See It, Now You Don’t: Star Formation Truncation Precedes the Loss of Molecular Gas by ∼100 Myr in Massive Poststarburst Galaxies at z ∼ 0.6

   https://doi.org/10.3847/1538-4357/ac3dfa  

   Bezanson, Rachel ; Spilker, Justin S. ; Suess, Katherine A. ; Setton, David J. ; Feldmann, Robert ; Greene, Jenny E. ; Kriek, Mariska ; Narayanan, Desika ; Verrico, Margaret ( February 2022 , The Astrophysical Journal)

   We use ALMA observations of CO(2–1) in 13 massive (M_*≳ 10¹¹M_⊙) poststarburst galaxies atz∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu$$\overrightarrow{L}\mathrm{ar}$$momentum, and Evolution ($\mathit{SQuIGG}\vec{L}E$) program. Early results showed that two poststarburst galaxies host large H₂reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with$M_{{\mathrm{H}}_2}\gtrsim {10}^9$M_⊙. Given their high stellar masses, this mass limit corresponds to an average gas fraction of$〈f_{{\mathrm{H}}_2}\equiv M_{{\mathrm{H}}_2}/M_{*}〉\sim 7\%$or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with theD_n4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H₂reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, the$\mathit{SQuIGG}\vec{L}E$galaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H₂scaling relations.

    

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2. Extreme Mass Loss in Low-mass Type Ib/c Supernova Progenitors

   https://doi.org/10.3847/2041-8213/ac9b3d  

   Wu, Samantha C. ; Fuller, Jim ( November 2022 , The Astrophysical Journal Letters)

   Many core-collapse supernovae (SNe) with hydrogen-poor and low-mass ejecta, such as ultra-stripped SNe and type Ibn SNe, are observed to interact with dense circumstellar material (CSM). These events likely arise from the core collapse of helium stars that have been heavily stripped by a binary companion and have ejected significant mass during the last weeks to years of their lives. In helium star models run to days before core collapse we identify a range of helium core masses ≈2.5–3M_⊙whose envelopes expand substantially due to the helium shell burning while the core undergoes neon and oxygen burning. When modeled in binary systems, the rapid expansion of these helium stars induces extremely high rates of late-stage mass transfer ($\dot{M}\gtrsim {10}^{-2}{M}_{\odot }{\mathrm{yr}}^{-1}$) beginning weeks to decades before core collapse. We consider two scenarios for producing CSM in these systems: either mass transfer remains stable and mass loss is driven from the system in the vicinity of the accreting companion, or mass transfer becomes unstable and causes a common envelope event (CEE) through which the helium envelope is unbound. The ensuing CSM properties are consistent with the CSM masses (∼10⁻²–1M_⊙) and radii (∼10¹³–10¹⁶cm) inferred for ultra-stripped SNe and several type Ibn SNe. Furthermore, systems that undergo a CEE could produce short-period neutron star binaries that merge in less than 100 Myr.

    

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3. Strong Variability in AzV 493, an Extreme Oe-type Star in the SMC

   https://doi.org/10.3847/1538-4357/acb690  

   Oey, M. S. ; Castro, N. ; Renzo, M. ; Vargas-Salazar, I. ; Suffak, M. W. ; Ratajczak, M. ; Monnier, J. D. ; Szymanski, M. K. ; Phillips, G. D. ; Calvet, N. ; et al ( April 2023 , The Astrophysical Journal)

   We present 18 yr of OGLE photometry together with spectra obtained over 12 yr revealing that the early Oe star AzV 493 shows strong photometric (ΔI< 1.2 mag) and spectroscopic variability with a dominant, 14.6 yr pattern and ∼40 day oscillations. We estimate the stellar parametersT_eff= 42,000 K,$\log L/L_{\odot }=5.83\pm 0.15$,M/M_⊙= 50 ± 9, andvsini= 370 ± 40 km s⁻¹. Direct spectroscopic evidence shows episodes of both gas ejection and infall. There is no X-ray detection, and it is likely a runaway star. The star AzV 493 may have an unseen companion on a highly eccentric (e> 0.93) orbit. We propose that close interaction at periastron excites ejection of the decretion disk, whose variable emission-line spectrum suggests separate inner and outer components, with an optically thick outer component obscuring both the stellar photosphere and the emission-line spectrum of the inner disk at early phases in the photometric cycle. It is plausible that AzV 493’s mass and rotation have been enhanced by binary interaction followed by the core-collapse supernova explosion of the companion, which now could be either a black hole or a neutron star. This system in the Small Magellanic Cloud can potentially shed light on OBe decretion disk formation and evolution, massive binary evolution, and compact binary progenitors.

    

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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. Bridging Scales in Black Hole Accretion and Feedback: Magnetized Bondi Accretion in 3D GRMHD

   https://doi.org/10.3847/2041-8213/ad1048  

   Cho 조, Hyerin 혜린 ; Prather, Ben S. ; Narayan, Ramesh ; Natarajan, Priyamvada ; Su, Kung-Yi ; Ricarte, Angelo ; Chatterjee, Koushik ( December 2023 , The Astrophysical Journal Letters)

   Fueling and feedback couple supermassive black holes (SMBHs) to their host galaxies across many orders of magnitude in spatial and temporal scales, making this problem notoriously challenging to simulate. We use a multi-zone computational method based on the general relativistic magnetohydrodynamic (GRMHD) code KHARMA that allows us to span 7 orders of magnitude in spatial scale, to simulate accretion onto a non-spinning SMBH from an external medium with a Bondi radius ofR_B≈ 2 × 10⁵GM_•/c², whereM_•is the SMBH mass. For the classic idealized Bondi problem, spherical gas accretion without magnetic fields, our simulation results agree very well with the general relativistic analytic solution. Meanwhile, when the accreting gas is magnetized, the SMBH magnetosphere becomes saturated with a strong magnetic field. The density profile varies as ∼r⁻¹rather thanr^−3/2and the accretion rate$\dot{M}$is consequently suppressed by over 2 orders of magnitude below the Bondi rate${\dot{M}}_{\mathrm{B}}$. We find continuous energy feedback from the accretion flow to the external medium at a level of$\sim {10}^{-2}\dot{M}{c}^2\sim 5\times {10}^{-5}{\dot{M}}_{\mathrm{B}}{c}^2$. Energy transport across these widely disparate scales occurs via turbulent convection triggered by magnetic field reconnection near the SMBH. Thus, strong magnetic fields that accumulate on horizon scales transform the flow dynamics far from the SMBH and naturally explain observed extremely low accretion rates compared to the Bondi rate, as well as at least part of the energy feedback.

    

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