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1. SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova

   https://doi.org/10.3847/2041-8213/ace4ca  

   Kilpatrick, Charles D. ; Foley, Ryan J. ; Jacobson-Galán, Wynn V. ; Piro, Anthony L. ; Smartt, Stephen J. ; Drout, Maria R. ; Gagliano, Alexander ; Gall, Christa ; Hjorth, Jens ; Jones, David O. ; et al ( July 2023 , The Astrophysical Journal Letters)

   We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HSTRband to Spitzer 4.5μm. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600R_⊙circumstellar shell of dusty material with a mass ∼5 × 10⁻⁵M_⊙surrounding a$\log (L/L_{\odot })=4.74\pm 0.07$and$T_{\mathrm{eff}}={3920}_{-160}^{+200}$K RSG. This luminosity is consistent with RSG models of initial mass 11M_⊙, depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5μm imaging, exhibiting ∼70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent withκ-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such asαOrionis (Betelgeuse).

    

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2. The Stellar Mass–Black Hole Mass Relation at z ∼ 2 down to BH∼107M⊙ Determined by HETDEX

   https://doi.org/10.3847/1538-4357/acc2c2  

   Zhang, Yechi ; Ouchi, Masami ; Gebhardt, Karl ; Liu, Chenxu ; Harikane, Yuichi ; Cooper, Erin Mentuch ; Davis, Dustin ; Farrow, Daniel J. ; Gawiser, Eric ; Hill, Gary J. ; et al ( May 2023 , The Astrophysical Journal)

   We investigate the stellar mass–black hole mass (${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$) relation with type 1 active galactic nuclei (AGNs) down to${\mathit{}}_{\mathrm{BH}}={10}^7{M}_{\odot }$, corresponding to a ≃ −21 absolute magnitude in rest-frame ultraviolet, atz= 2–2.5. Exploiting the deep and large-area spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGNs with${\mathit{}}_{\mathrm{BH}}$ranging from 10⁷–10¹⁰M_⊙that are measured with single-epoch virial method using Civemission lines detected in the HETDEX spectra.${\mathit{}}_{*}$of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, the Wide-field Infrared Survey Explorer, and ground-based 4–8 m class telescopes byCIGALEspectral energy distribution (SED) fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially resolved host galaxies with the James Webb Space Telescope/NIRCam CEERS data. We obtain the${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation covering the unexplored low-mass ranges of${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$, and conduct forward modeling to fully account for the selection biases and observational uncertainties. The intrinsic${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation atz∼ 2 has a moderate positive offset of 0.52 ± 0.14 dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$. Our${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation is inconsistent with the${\mathit{}}_{\mathrm{BH}}$suppression at the low-${\mathit{}}_{*}$regime predicted by recent hydrodynamic simulations at a 98% confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations.

    

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3. An Exceptional Dimming Event for a Massive, Cool Supergiant in M51

   https://doi.org/10.3847/1538-4357/ac626c  

   Jencson, Jacob E. ; Sand, David J. ; Andrews, Jennifer E. ; Smith, Nathan ; Pearson, Jeniveve ; Strader, Jay ; Valenti, Stefano ; Beasor, Emma R. ; Rothberg, Barry ( May 2022 , The Astrophysical Journal)

   We present the discovery of an exceptional dimming event in a cool supergiant star in the Local Volume spiral M51. The star, dubbed M51-DS1, was found as part of a Hubble Space Telescope (HST) search for failed supernovae (SNe). The supergiant, which is plausibly associated with a very young (≲6 Myr) stellar population, showed clear variability (amplitude ΔF814W≈ 0.7 mag) in numerous HST images obtained between 1995 and 2016, before suddenly dimming by >2 mag inF814Wsometime between late 2017 and mid-2019. In follow-up data from 2021, the star rebrightened, ruling out a failed supernova. Prior to its near-disappearance, the star was luminous and red (M_F814W≲ − 7.6 mag,F606W−F814W= 1.9–2.2 mag). Modeling of the pre-dimming spectral energy distribution of the star favors a highly reddened, very luminous ($\log [L/L_{\odot }]=5.4$–5.7) star withT_eff≈ 3700–4700 K, indicative of a cool yellow or post-red supergiant (RSG) with an initial mass of ≈26–40M_⊙. However, the local interstellar extinction and circumstellar extinction are uncertain, and could be lower: the near-IR colors are consistent with an RSG, which would be cooler (T_eff≲ 3700 K) and slightly less luminous ($\log [L/L_{\odot }]=5.2$–5.3), giving an inferred initial mass of ≈19–22M_⊙. In either case, the dimming may be explained by a rare episode of enhanced mass loss that temporarily obscures the star, potentially a more extreme counterpart to the 2019–2020 “Great Dimming” of Betelgeuse. Given the emerging evidence that massive evolved stars commonly exhibit variability that can mimic a disappearing star, our work highlights a substantial challenge in identifying true failed SNe.

    

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4. The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and Its Implications for Structure Growth

   https://doi.org/10.3847/1538-4357/acfe06  

   Qu, Frank J. ; Sherwin, Blake D. ; Madhavacheril, Mathew S. ; Han, Dongwon ; Crowley, Kevin T. ; Abril-Cabezas, Irene ; Ade, Peter A. R. ; Aiola, Simone ; Alford, Tommy ; Amiri, Mandana ; et al ( February 2024 , The Astrophysical Journal)

   We present new measurements of cosmic microwave background (CMB) lensing over 9400 deg²of the sky. These lensing measurements are derived from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB data set, which consists of five seasons of ACT CMB temperature and polarization observations. We determine the amplitude of the CMB lensing power spectrum at 2.3% precision (43σsignificance) using a novel pipeline that minimizes sensitivity to foregrounds and to noise properties. To ensure that our results are robust, we analyze an extensive set of null tests, consistency tests, and systematic error estimates and employ a blinded analysis framework. Our CMB lensing power spectrum measurement provides constraints on the amplitude of cosmic structure that do not depend on Planck or galaxy survey data, thus giving independent information about large-scale structure growth and potential tensions in structure measurements. The baseline spectrum is well fit by a lensing amplitude ofA_lens= 1.013 ± 0.023 relative to the Planck 2018 CMB power spectra best-fit ΛCDM model andA_lens= 1.005 ± 0.023 relative to the ACT DR4 + WMAP best-fit model. From our lensing power spectrum measurement, we derive constraints on the parameter combination$S_8^{\mathrm{CMBL}}\equiv {\sigma }_8{\left({\mathrm{\Omega }}_m/0.3\right)}^{0.25}$of$S_8^{\mathrm{CMBL}}=0.818\pm 0.022$from ACT DR6 CMB lensing alone and$S_8^{\mathrm{CMBL}}=0.813\pm 0.018$when combining ACT DR6 and PlanckNPIPECMB lensing power spectra. These results are in excellent agreement with ΛCDM model constraints from Planck or ACT DR4 + WMAP CMB power spectrum measurements. Our lensing measurements from redshiftsz∼ 0.5–5 are thus fully consistent with ΛCDM structure growth predictions based on CMB anisotropies probing primarilyz∼ 1100. We find no evidence for a suppression of the amplitude of cosmic structure at low redshifts.

    

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5. Uniform Forward-modeling Analysis of Ultracool Dwarfs. III. Late-M and L Dwarfs in Young Moving Groups, the Pleiades, and the Hyades

   https://doi.org/10.3847/1538-4357/ad0b12  

   Hurt, Spencer A. ; Liu, Michael C. ; Zhang, Zhoujian ; Phillips, Mark ; Allers, Katelyn N. ; Deacon, Niall R. ; Aller, Kimberly M. ; Best, William M. J. ( January 2024 , The Astrophysical Journal)

   We present a uniform forward-modeling analysis of 90 late-M and L dwarfs in nearby young (∼10–200 Myr) moving groups, the Pleiades, and the Hyades using low-resolution (R≈ 150) near-infrared (0.9–2.4μm) spectra and the BT-Settl model atmospheres. We derive the objects’ effective temperatures, surface gravities, radii, and masses by comparing our spectra to the models using a Bayesian framework with nested sampling and calculate the same parameters using evolutionary models. Assuming the evolutionary-based parameters are more robust, our spectroscopically inferred parameters from BT-Settl exhibit two types of systematic behavior for objects near the M-L spectral type boundary. Several objects are clustered aroundT_eff≈ 1800 K and$\log g\approx 5.5$dex, implying impossibly large masses (150–1400M_Jup), while others are clustered aroundT_eff≳ 3000 K and$\log g\lesssim 3.0$dex, implying unphysically low masses and unreasonably young ages. We find the fitted BT-Settl model spectra tend to overpredict the peakJ- andH-band flux for objects located near the M-L boundary, suggesting the dust content included in the model atmospheres is insufficient to match the observations. By adding an interstellar medium–like reddening law to the BT-Settl model spectra, we find the fits between models and observed spectra are greatly improved, with the largest reddening coefficients occurring at the M-L transition. This work delivers a systematic examination of the BT-Settl model atmospheres and constitutes the largest spectral analysis of benchmark late-M- and L-type brown dwarfs to date.

    

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