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1. Modeling ALMA Observations of the Warped Molecular Gas Disk in the Red Nugget Relic Galaxy NGC 384

   https://doi.org/10.3847/1538-4357/ad7bb0  

   Cohn, Jonathan H; Curliss, Maeve; Walsh, Jonelle L; Kabasares, Kyle M; Boizelle, Benjamin D; Barth, Aaron J; Gebhardt, Karl; Gültekin, Kayhan; Buote, David A; Darling, Jeremy; et al (November 2024, The Astrophysical Journal)

   We present 0.22" resolution CO(2–1) observations of the circumnuclear gas disk in the local compact galaxy NGC 384 with the Atacama Large Millimeter/submillimeter Array (ALMA). While the majority of the disk displays regular rotation with projected velocities rising to 370 km/s, the inner ~0.5" exhibits a kinematic twist. We develop warped disk gas-dynamical models to account for this twist, fit those models to the ALMA data cube, and find a stellar mass-to-light ratio in the H-band of M/L_H = 1.34 ± 0.01 [1σ statistical] ±0.02 [systematic] M⊙/L⊙ and a supermassive black hole (BH) mass (M_BH) of M_BH = (7.26_{−0.48}^{+0.43} [1σ statistical]_{-1.00}^{+0.55} [systematic]x10^8 M⊙. In contrast to most previous dynamical M_BH measurements in local compact galaxies, which typically found over-massive BHs compared to the local BH mass−bulge luminosity and BH mass−bulge mass relations, NGC 384 lies within the scatter of those scaling relations. NGC 384 and other local compact galaxies are likely relics of z~2 red nuggets, and over-massive BHs in these relics indicate BH growth may conclude before the host galaxy stars have finished assembly. Our NGC 384 results may challenge this evolutionary picture, suggesting there may be increased scatter in the scaling relations than previously thought. However, this scatter could be inflated by systematic differences between stellar- and gas-dynamical measurement methods, motivating direct comparisons between the methods for NGC 384 and the other compact galaxies in the sample. 

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2. Black Hole Mass Measurements of Early-type Galaxies NGC 1380 and NGC 6861 through ALMA and HST Observations and Gas-dynamical Modeling*

   https://doi.org/10.3847/1538-4357/ac7a38  

   Kabasares, Kyle M.; Barth, Aaron J.; Buote, David A.; Boizelle, Benjamin D.; Walsh, Jonelle L.; Baker, Andrew J.; Darling, Jeremy; Ho, Luis C.; Cohn, Jonathan (August 2022, The Astrophysical Journal)

   Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of CO(2–1) emission from the circumnuclear disks in two early-type galaxies, NGC 1380 and NGC 6861. The disk in each galaxy is highly inclined ( i ∼ 75°), and the projected velocities of the molecular gas near the galaxy centers are ∼300 km s −1 in NGC 1380 and ∼500 km s −1 in NGC 6861. We fit thin disk dynamical models to the ALMA data cubes to constrain the masses of the central black holes (BHs). We created host galaxy models using Hubble Space Telescope images for the extended stellar mass distributions and incorporated a range of plausible central dust extinction values. For NGC 1380, our best-fit model yields M BH = 1.47 × 10 8 M ⊙ with a ∼40% uncertainty. For NGC 6861, the lack of dynamical tracers within the BH’s sphere of influence due to a central hole in the gas distribution precludes a precise measurement of M BH . However, our model fits require a value for M BH in the range of (1–3) × 10 9 M ⊙ in NGC 6861 to reproduce the observations. The BH masses are generally consistent with predictions from local BH–host galaxy scaling relations. Systematic uncertainties associated with dust extinction of the host galaxy light and choice of host galaxy mass model dominate the error budget of both measurements. Despite these limitations, the measurements demonstrate ALMA’s ability to provide constraints on BH masses in cases where the BH’s projected radius of influence is marginally resolved or the gas distribution has a central hole. 

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3. Running late: testing delayed supermassive black hole growth models against the quasar luminosity function

   https://doi.org/10.1093/mnras/stac398  

   Tillman, Megan Taylor; Wellons, Sarah; Faucher-Giguère, Claude-André; Kelley, Luke Zoltan; Anglés-Alcázar, Daniel (March 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Observations of massive galaxies at low redshift have revealed approximately linear scaling relations between the mass of a supermassive black hole (SMBH) and properties of its host galaxy. How these scaling relations evolve with redshift and whether they extend to lower-mass galaxies, however, remain open questions. Recent galaxy formation simulations predict a delayed, or ‘two-phase,’ growth of SMBHs: slow, highly intermittent BH growth due to repeated gas ejection by stellar feedback in low-mass galaxies, followed by more sustained gas accretion that eventually brings BHs on to the local scaling relations. The predicted two-phase growth implies a steep increase, or ‘kink,’ in BH-galaxy scaling relations at a stellar mass $$\rm {M}_{*}\sim 5\times 10^{10}$$ M⊙. We develop a parametric, semi-analytic model to compare different SMBH growth models against observations of the quasar luminosity function (QLF) at z ∼ 0.5−4. We compare models in which the relation between SMBH mass and galaxy mass is purely linear versus two-phase models. The models are anchored to the observed galaxy stellar mass function, and the BH mass functions at different redshifts are consistently connected by the accretion rates contributing to the QLF. The best fits suggest that two-phase evolution is significantly preferred by the QLF data over a purely linear scaling relation. Moreover, when the model parameters are left free, the two-phase model fits imply a transition mass consistent with that predicted by simulations. Our analysis motivates further observational tests, including measurements of BH masses and active galactic nuclei activity at the low-mass end, which could more directly test two-phase SMBH growth. 

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4. Circumnuclear Dust in Luminous Early-type Galaxies. I. Sample Properties and Stellar Luminosity Models

   https://doi.org/10.3847/1538-4357/ad5be4  

   Davidson, Jared R; Boizelle, Benjamin D; Walsh, Jonelle L; Barth, Aaron J; Rasmussen, Emma; Baker, Andrew J; Buote, David A; Darling, Jeremy; Ho, Luis C; Kabasares, Kyle M; et al (August 2024, The Astrophysical Journal)

   Dusty circumnuclear disks (CNDs) in luminous early-type galaxies (ETGs) show regular, dynamically cold molecular gas kinematics. For a growing number of ETGs, Atacama Large Millimeter/sub-millimeter Array (ALMA) CO imaging and detailed gas-dynamical modeling facilitate moderate-to-high precision black hole (BH) mass (M_BH) determinations. From the ALMA archive, we identified a subset of 26 ETGs with estimated M_BH/Msun ≳ 10^8 to a few x 10^9 and clean CO kinematics but that previously did not have sufficiently high-angular-resolution near-IR observations to mitigate dust obscuration when constructing stellar luminosity models. We present new optical and near-IR Hubble Space Telescope (HST) images of this sample to supplement the archival HST data, detailing the sample properties and data-analysis techniques. After masking the most apparent dust features, we measure stellar surface-brightness profiles and model the luminosities using the multi-Gaussian expansion (MGE) formalism. Some of these MGEs have already been used in CO dynamical modeling efforts to secure quality M_BH determinations, and the remaining ETG targets here are expected to significantly improve the high-mass end of the current BH census, facilitating new scrutiny of local BH mass–host galaxy scaling relationships. We also explore stellar isophotal behavior and general dust properties, finding these CNDs generally become optically thick in the near-IR (A_H ≳ 1 mag). These CNDs are typically well aligned with the larger-scale stellar photometric axes, with a few notable exceptions. Uncertain dust impact on the MGE often dominates the BH mass error budget, so extensions of this work will focus on constraining CND dust attenuation. 

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5. Growth of massive black holes in FFB galaxies at cosmic dawn

   https://doi.org/10.1051/0004-6361/202452393  

   Dekel, Avishai; Stone, Nicholas C; Chowdhury, Dhruba Dutta; Gilbaum, Shmuel; Li, Zhaozhou; Mandelker, Nir; van_den_Bosch, Frank C (March 2025, Astronomy & Astrophysics)

   Aims.The scenario of feedback-free starbursts (FFB), which predicts excessively bright galaxies at cosmic dawn as observed using JWST, may provide a natural setting for black hole (BH) growth. This involves the formation of intermediate-mass seed BHs and their runaway mergers into super-massive BHs with high BH-to-stellar mass ratios and low Active Galactic Nucleus (AGN) luminosities. Methods.We present a scenario of merger-driven BH growth in FFB galaxies and study its feasibility. Results.Black hole seeds form within the building blocks of the FFB galaxies, namely, thousands of compact star clusters, each starbursting in a free-fall time of a few million years before the onset of stellar and supernova feedback. The BH seeds form by rapid core collapse in the FFB clusters, in a few free-fall times, which is sped up by the migration of massive stars due to the young, broad stellar mass function and stimulated by a “gravo-gyro” instability due to internal cluster rotation and flattening. BHs of ∼10⁴ M_⊙are expected in ∼10⁶ M_⊙FFB clusters within sub-kiloparsec galactic disks atz​ ∼ ​10. The BHs then migrate to the galaxy center by dynamical friction, hastened by the compact FFB stellar galactic disk configuration. Efficient mergers of the BH seeds will produce ∼10^6 − 8 M_⊙BHs with a BH-to-stellar mass ratio ∼0.01 byz​ ∼ ​4 − 7, as observed. The growth of the central BH by mergers can overcome the bottleneck introduced by gravitational wave recoils if the BHs inspiral within a relatively cold disk or if the escape velocity from the galaxy is boosted by a wet compaction event. Such events, common in massive galaxies at high redshifts, can also help by speeding up the inward BH migration and by providing central gas to assist with the final parsec problem. Conclusions.The cold disk version of the FFB scenario provides a feasible route for the formation of supermassive BHs. 

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