@article{21084, abstract = {Self-assembly is a powerful method to obtain large discrete functional molecular architectures. When using a single building block, self-assembly generally yields symmetrical objects in which all the subunits relate similarly to their neighbours. Here we report the discovery of a family of self-constructing cyclic macromolecules with stable folded conformations of low symmetry, which include some with a prime number (13, 17 and 23) of units, despite being formed from a single component. The formation of these objects amounts to the production of polymers with a perfectly uniform length. Design rules for the spontaneous emergence of such macromolecules include endowing monomers with a strong potential for non-covalent interactions that remain frustrated in competing entropically favoured yet conformationally restrained smaller cycles. The process can also be templated by a guest molecule that itself has an asymmetrical structure, which paves the way to molecular imprinting techniques at the level of single polymer chains.}, author = {Pappas, Charalampos G. and Mandal, Pradeep K and Liu, Bin and Kauffmann, Brice and Miao, Xiaoming and Komáromy, Dávid and Hoffmann, Waldemar and Manz, Christian and Chang, Rayoon and Liu, Kai and Pagel, Kevin and Huc, Ivan and Otto, Sijbren}, issn = {1755-4349}, journal = {Nature Chemistry}, number = {12}, pages = {1180--1186}, publisher = {Springer Nature}, title = {{Emergence of low-symmetry foldamers from single monomers}}, doi = {10.1038/s41557-020-00565-2}, volume = {12}, year = {2020}, } @article{21085, abstract = {Foldamers combining aliphatic and aromatic main-chain units often produce atypical structures that cannot easily be accessed from purely aromatic or aliphatic sequences. We report solid-state evidence that sequences comprising α-amino acids and quinoline-based monomers adopt conformations that combine the folding propensities of both components. Foldamers 2 and 3 having an XQQ repeat motif (X=α-amino acid, Q=quinoline) were synthesized. Crystals of 2 (X=Phe, Q with an anionic side chain) obtained from water revealed an aromatic helix where amide groups belonging to the α-amino acids created a hydrogen-bond array typical of peptidic helices. Crystals of 3 (X=Ser, Q with a lipophilic side chain) obtained from organic solvents revealed a helix-turn-helix structure in which α-amino acid side chains interfere with main-chain hydrogen bonding. High sequence-dependency of the conformation is typical of peptides but is shown here to include aromatic folding features.}, author = {Hu, Xiaobo and Mandal, Pradeep K and Kauffmann, Brice and Huc, Ivan}, issn = {2192-6506}, journal = {ChemPlusChem}, number = {7}, pages = {1580--1586}, publisher = {Wiley}, title = {{Hybrid sequences that express both aromatic amide and α‐peptidic folding features}}, doi = {10.1002/cplu.202000416}, volume = {85}, year = {2020}, } @misc{17444, abstract = {The first wafer-scale growth of site-controlled Ge/Si nanowires is reported by Georgios Katsaros, Jian-Jun Zhang, and co-workers in article number 1906523. They are highly uniform and their position, distance, length, and even square- or L-shaped structures can all be precisely controlled. The electrically tunable spin-orbit coupling demonstrated by transport measurements and the charge sensing between quantum dots in closely spaced wires open a path toward scalable qubit devices using nanowires on silicon.}, author = {Gao, Fei and Wang, Jian‐Huan and Watzinger, Hannes and Hu, Hao and Rančić, Marko J. and Zhang, Jie‐Yin and Wang, Ting and Yao, Yuan and Wang, Gui‐Lei and Kukucka, Josip and Vukušić, Lada and Kloeffel, Christoph and Loss, Daniel and Liu, Feng and Katsaros, Georgios and Zhang, Jian‐Jun}, booktitle = {Advanced Materials}, issn = {1521-4095}, number = {16}, publisher = {Wiley}, title = {{Nanowires: Site‐controlled uniform Ge/Si Hut wires with electrically tunable spin–orbit coupling (Adv. Mater. 16/2020)}}, doi = {10.1002/adma.202070122}, volume = {32}, year = {2020}, } @article{17524, abstract = {The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disc of a supermassive black hole are expected to produce correlated flux variations in ultraviolet (UV) and optical bands. Recent work has further argued that binary quasars should exhibit strongly correlated UV and optical periodicities. Strong UV–optical correlations have indeed been established in small samples of (N ≲ 30) quasars with well-sampled light curves, and have extended the ‘bluer-when-brighter’ trend previously found within the optical bands. Here, we further test the nature of quasar variability by examining the observed-frame UV–optical correlations among bright quasars extracted from the Half Million Quasars (HMQ) catalogue. We identified a large sample of 1315 quasars in HMQ with overlapping UV and optical light curves from the Galaxy Evolution Explorer and the Catalina Real-time Transient Survey, respectively. We find that strong correlations exist in this much larger sample, but we rule out, at ∼95 per cent confidence, the simple hypothesis that the intrinsic UV and optical variations of all quasars are fully correlated. Our results therefore imply the existence of physical mechanism(s) that can generate uncorrelated optical and UV flux variations.}, author = {Xin, Chengcheng and Charisi, Maria and Haiman, Zoltán and Schiminovich, David}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {1403--1413}, publisher = {Oxford University Press}, title = {{Correlation between optical and UV variability of a large sample of quasars}}, doi = {10.1093/mnras/staa1258}, volume = {495}, year = {2020}, } @article{17528, abstract = {We performed a series of numerical experiments to quantify the sensitivity of the predictions for weak lensing statistics obtained in ray-tracing dark matter (DM)-only simulations, to two hyper-parameters that influence the accuracy as well as the computational cost of the predictions: the thickness of the lens planes used to build past light cones and the mass resolution of the underlying DM simulation. The statistics considered are the power spectrum (PS) and a series of non-Gaussian observables, including the one-point probability density function, lensing peaks, and Minkowski functionals. Counterintuitively, we find that using thin lens planes (< 60 h−1 Mpc on a 240 h−1 Mpc simulation box) suppresses the PS over a broad range of scales beyond what would be acceptable for a survey comparable to the Large Synoptic Survey Telescope (LSST). A mass resolution of 7.2 × 1011 h−1 M⊙ per DM particle (or 2563 particles in a (240 h−1 Mpc)3 box) is sufficient to extract information using the PS and non-Gaussian statistics from weak lensing data at angular scales down to 1' with LSST-like levels of shape noise.}, author = {Matilla, José Manuel Zorrilla and Waterval, Stefan and Haiman, Zoltán}, issn = {0004-6256}, journal = {The Astronomical Journal}, number = {6}, publisher = {American Astronomical Society}, title = {{Optimizing simulation parameters for weak lensing analyses involving non-Gaussian observables}}, doi = {10.3847/1538-3881/ab8f8c}, volume = {159}, year = {2020}, } @article{17529, abstract = {The astrophysical origin of gravitational wave (GW) events is one of the most timely problems in the wake of the LIGO/Virgo discoveries. In active galactic nuclei (AGN), binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Previous studies have suggested that binary black hole (BBH) mergers in AGN disks can contribute significantly to BBH mergers observed by GW interferometers. Here we examine the distribution of the effective spin parameter χeff of this GW source population. We extend our semi-analytical model of binary formation and evolution in AGN disks by following the evolution of the binary orbital angular momenta and black hole (BH) spins. BH spins change due to gas accretion and BH mergers, while the binary orbital angular momenta evolve due to gas accretion and binary-single interactions. We find that the distribution of χeff predicted by our AGN model is similar to the distribution observed during LIGO/Virgo O1 and O2. On the other hand, if radial migration of BHs is inefficient, χeff is skewed toward higher values compared with the observed distribution, because of the paucity of scattering events that would randomize spin directions relative to the orbital plane. We suggest that high binary masses and the positive correlation between binary mass and the standard deviation of χeff for chirp masses up to ≈20 M⊙, can be possible signatures for mergers originating in AGN disks. Finally, hierarchical mergers in AGN disks naturally produce properties of the recent GW event GW190412, including a low mass ratio, a high primary BH spin, and a significant spin component in the orbital plane.}, author = {Tagawa, Hiromichi and Haiman, Zoltán and Bartos, Imre and Kocsis, Bence}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, publisher = {American Astronomical Society}, title = {{Spin evolution of stellar-mass black hole binaries in active galactic nuclei}}, doi = {10.3847/1538-4357/aba2cc}, volume = {899}, year = {2020}, } @article{17537, abstract = {The recent gravitational wave merger event, GW190521, has challenged our understanding of the stellar-mass black hole (BH) formation. The primary and secondary BH are both inferred to fall inside the pair-instability (PI) mass gap. Here we propose that the formation of such binaries is possible through gas accretion onto the BH remnants of Population III (Pop~III) stars born in high-redshift (z>10) minihalos. Once the parent halo has grown to the atomic-cooling limit, even brief episodes of gas accretion in the dense central regions of the halo can increase the masses of Pop~III remnant BHs above the PI limit. Starting with a BBH with an initial mass of O(100) M⊙ we find that it would only need to spend about 100~Myr in the inner few pc of an atomic-cooling halo to accrete about 50~M⊙ of material and resemble a system similar to GW190521. The dynamical friction timescale for the binary to sink to the dense inner region of its parent halo is comparable or shorter than the accretion timescale required to increase their mass above the PI limit. Once in the core of the halo, the binary can enter a phase of hyper-Eddington accretion, where it would only take a few thousand years to exceed the PI limit through accretion. Even more massive BBHs could form through this channel, and be detectable by detectors with improved low-frequency sensitivity. Single Pop~III BH remnants would also grow through accretion and could later form binaries dynamically. As little as a few percent of Pop~III BH remnants may be sufficient to match the rate of massive BBH mergers inferred from GW190521 of 0.13+0.3−0.11Gpc−3yr−1.}, author = {Safarzadeh, Mohammadtaher and Haiman, Zoltán}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {American Astronomical Society}, title = {{Formation of GW190521 via gas accretion onto population III stellar black hole remnants born in high-redshift minihalos}}, doi = {10.3847/2041-8213/abc253}, volume = {903}, year = {2020}, } @article{17538, abstract = {Recent three-dimensional cosmological simulations of protogalaxy formation have suggested that supermassive stars (SMSs) can form in gas clouds in which H2 cooling is suppressed by dynamical heating prior to the activation of atomic cooling (Wise et al. 2019), but they stopped short of the following growth of a central protostar. Here we examine whether accretion on the protostellar core in this cloud is sufficiently rapid, in the face of the radiation feedback, to produce a SMS. We perform one-dimensional radiation-hydrodynamical simulations of the hot collapsing cloud with non-equilibrium chemical reactions directly adopting the cloud properties from Wise et al. (2019) as an initial condition. We find that the stellar Lyman-Werner (LW) radiation from the SMS dissociates H2 in the inner regions of the gas flow, increasing gas temperature and thermal pressure, and temporarily stopping the accretion. However, this negative feedback ceases when the self-gravity and inward ram pressure force on larger scales push the gas inward. The central protostar is unable to expand an HII region due to the high density, and grows to a mass of ≳105M⊙. Our results suggests the successful formation of SMSs, and resulting massive (∼105M⊙) remnant black holes in the clouds, but need to be confirmed in two- or three-dimensional simulations.}, author = {Sakurai, Yuya and Haiman, Zoltán and Inayoshi, Kohei}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {5960--5971}, publisher = {Oxford University Press}, title = {{Radiative feedback for supermassive star formation in a massive cloud with H2 molecules in an atomic-cooling halo}}, doi = {10.1093/mnras/staa3227}, volume = {499}, year = {2020}, } @article{17540, abstract = {Among the potential milliHz gravitational wave (GW) sources for the upcoming space-based interferometer LISA are extreme- or intermediate-mass ratio inspirals (EMRI/IMRIs). These events involve the coalescence of supermassive black holes in the mass range 105M⊙≲M≲107M⊙ with companion BHs of much lower masses. A subset of E/IMRIs are expected to occur in the accretion discs of active galactic nuclei (AGN), where torques exerted by the disc can interfere with the inspiral and cause a phase shift in the GW waveform. Here we use a suite of two-dimensional hydrodynamical simulations with the moving-mesh code DISCO to present a systematic study of disc torques. We measure torques on an inspiraling BH and compute the corresponding waveform deviations as a function of the binary mass ratio q≡M2/M1, the disc viscosity (α), and gas temperature (or equivalently Mach number; M). We find that the absolute value of the gas torques is within an order of magnitude of previously determined planetary migration torques, but their precise value and sign depends non-trivially on the combination of these parameters. The gas imprint is detectable by LISA for binaries embedded in AGN discs with surface densities above Σ0≥104−6gcm−2, depending on q, α and M. Deviations are most pronounced in discs with higher viscosities, and for E/IMRIs detected at frequencies where LISA is most sensitive. Torques in colder discs exhibit a noticeable dependence on the GW-driven inspiral rate as well as strong fluctuations at late stages of the inspiral. Our results further suggest that LISA may be able to place constraints on AGN disc parameters and the physics of disc-satellite interaction.}, author = {Derdzinski, A and D’Orazio, D and Duffell, P and Haiman, Zoltán and MacFadyen, A}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {3540--3557}, publisher = {Oxford University Press}, title = {{Evolution of gas disc–embedded intermediate mass ratio inspirals in the LISA band}}, doi = {10.1093/mnras/staa3976}, volume = {501}, year = {2020}, } @article{17542, abstract = {We present a new semianalytic model of the formation of the first stars. Our method takes dark matter halo merger trees (including three-dimensional spatial information) from cosmological N-body simulations as input and applies analytic prescriptions to compute both the Population III and metal-enriched star formation histories. We have developed a novel method to accurately compute the major feedback processes affecting Population III star formation: H2 photodissociation from Lyman–Werner (LW) radiation, suppression of star formation due to inhomogeneous reionization, and metal enrichment via supernova winds. Our method utilizes a grid-based approach relying on fast Fourier transforms to rapidly track the LW intensity, ionization fraction, and metallicity in three dimensions throughout the simulation box. We present simulations for a wide range of astrophysical model parameters from z ≈ 30 to 6. Initially long-range LW feedback and local metal enrichment and reionization feedback dominate. However, for z ≲ 15 we find that the star formation rate density (SFRD) of Population III stars is impacted by the combination of external metal enrichment (metals from one halo polluting other pristine halos) and inhomogeneous reionization. We find that the interplay of these processes is particularly important for the Population III SFRD at z ≲ 10. Reionization feedback delays star formation long enough for metal bubbles to reach halos that would otherwise form Population III stars. Including these effects can lead to more than an order-of-magnitude decrease in the Population III SFRD at z = 6 compared to LW feedback alone.}, author = {Visbal, Eli and Bryan, Greg L. and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, publisher = {American Astronomical Society}, title = {{Self-consistent semianalytic modeling of feedback during primordial star formation and reionization}}, doi = {10.3847/1538-4357/ab994e}, volume = {897}, year = {2020}, } @article{17552, abstract = {We examine the light curves of two quasars, motivated by recent suggestions that a supermassive black hole binary (SMBHB) can exhibit sharp lensing spikes. We model the variability of each light curve as due to a combination of two relativistic effects: the orbital relativistic Doppler boost and gravitational binary self-lensing. In order to model each system we extend previous Doppler plus self-lensing models to include eccentricity. The first quasar is identified in optical data as a binary candidate with a 20-yr period (Ark 120), and shows a prominent spike. For this source, we rule out the lensing hypothesis and disfavor the Doppler-boost hypothesis due to discrepancies in the measured vs. recovered values of the binary mass and optical spectral slope. The second source, which we nickname Spikey, is the rare case of an active galactic nucleus (AGN) identified in Kepler's high-quality, high-cadence photometric data. For this source, we find a model, consisting of a combination of a Doppler modulation and a narrow symmetric lensing spike, consistent with an eccentric SMBHB with a total mass of approximately 30 million solar masses, rest-frame orbital period T=418 days, eccentricity e=0.5, and seen at an inclination of 8 degrees from edge-on. This interpretation can be tested by monitoring Spikey for periodic behavior and recurring flares in the next few years. In preparation for such monitoring we present the first X-ray observations of this object taken by the Neil Gehrels Swift observatory.}, author = {Hu, Betty X and D’Orazio, Daniel J and Haiman, Zoltán and Smith, Krista Lynne and Snios, Bradford and Charisi, Maria and Di Stefano, Rosanne}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {4061--4070}, publisher = {Oxford University Press}, title = {{Spikey: self-lensing flares from eccentric SMBH binaries}}, doi = {10.1093/mnras/staa1312}, volume = {495}, year = {2020}, } @article{17554, abstract = {The bright quasar PG1302-102 has been identified as a candidate supermassive black hole binary from its near-sinusoidal optical variability. While the significance of its optical periodicity has been debated due to the stochastic variability of quasars, its multiwavelength variability in the ultraviolet (UV) and optical bands is consistent with relativistic Doppler boost caused by the orbital motion in a binary. However, this conclusion was based previously on sparse UV data that were not taken simultaneously with the optical data. Here, we report simultaneous follow-up observations of PG1302-102 with the Ultraviolet Optical Telescope on the Neil Gehrels Swift Observatory in six optical + UV bands. The additional nine Swift observations produce light curves roughly consistent with the trend under the Doppler boost hypothesis, which predicts that UV variability should track the optical, but with a ∼2.2 times higher amplitude. We perform a statistical analysis to quantitatively test this hypothesis. We find that the data are consistent with the Doppler boost hypothesis when we compare the the amplitudes in optical B-band and UV light curves. However, the ratio of UV to V-band variability is larger than expected and is consistent with the Doppler model, only if either the UV/optical spectral slopes vary, the stochastic variability makes a large contribution in the UV, or the sparse new optical data underestimate the true optical variability. We have evidence for the latter from comparison with the optical light curve from All-Sky Automated Survey for Supernovae. Additionally, the simultaneous analysis of all four bands strongly disfavours the Doppler boost model whenever Swift V band is involved. Additional, simultaneous optical + UV observations tracing out another cycle of the 5.2-yr proposed periodicity should lead to a definitive conclusion.}, author = {Xin, Chengcheng and Charisi, Maria and Haiman, Zoltán and Schiminovich, David and Graham, Matthew J and Stern, Daniel and D’Orazio, Daniel J}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {1683--1696}, publisher = {Oxford University Press}, title = {{Testing the relativistic Doppler boost hypothesis for the binary candidate quasar PG1302-102 with multiband Swift data}}, doi = {10.1093/mnras/staa1643}, volume = {496}, year = {2020}, } @article{17564, abstract = {The existence of ≈10^9 Msun supermassive black holes (SMBHs) within the first billion year of the universe has stimulated numerous ideas for the prompt formation and rapid growth of BHs in the early universe. Here we review ways in which the seeds of massive BHs may have first assembled, how they may have subsequently grown as massive as ≈10^9 Msun, and how multi-messenger observations could distinguish between different SMBH assembly scenarios. We conclude the following: (1) The ultra-rare ≈10^9 Msun SMBHs represent only the tip of the iceberg. Early BHs likely fill a continuum from stellar-mass (approx. 10 Msun) to the super-massive (≈10^9 Msun) regime, reflecting a range of initial masses and growth histories. (2) Stellar-mass BHs were likely left behind by the first generation of stars at redshifts as high as z=30, but their initial growth was typically stunted due to the shallow potential wells of their host galaxies. (3) Conditions in some larger, metal-poor galaxies soon became conducive to the rapid formation and growth of massive `seed' holes, via gas accretion and by mergers in dense stellar clusters. (4) BH masses depend on the environment (such as the number and properties of nearby radiation sources and the local baryonic streaming velocity), and on the metal enrichment and assembly history of the host galaxy. (5) Distinguishing between assembly mechanisms will be difficult, but a combination of observations by LISA (probing massive BH growth via mergers) and by deep multi-wavelength electromagnetic observations (probing growth via gas accretion) is particularly promising.}, author = {Inayoshi, Kohei and Visbal, Eli and Haiman, Zoltán}, issn = {0066-4146}, journal = {Annual Review of Astronomy and Astrophysics}, number = {1}, pages = {27--97}, publisher = {Annual Reviews}, title = {{The Assembly of the First Massive Black Holes}}, doi = {10.1146/annurev-astro-120419-014455}, volume = {58}, year = {2020}, } @article{17566, abstract = {The formation of supermassive stars has generally been studied under the assumption of rapid accretion of pristine metal-free gas. Recently it was found, however, that gas enriched to metallicities up to Z∼10−3 Z⊙ can also facilitate supermassive star formation, as long as the total mass infall rate onto the protostar remains sufficiently high. We extend the analysis further by examining how the abundance of supermassive star candidate haloes would be affected if all haloes with super-critical infall rates, regardless of metallicity were included. We investigate this scenario by identifying all atomic cooling haloes in the Renaissance simulations with central mass infall rates exceeding a fixed threshold. We find that among these haloes with central mass infall rates above 0.1 M⊙ yr−1 approximately two-thirds of these haloes have metallicities of Z>10−3 Z⊙. If metal mixing within these haloes is inefficient early in their assembly and pockets of metal-poor gas can remain then the number of haloes hosting supermassive stars can be increased by at least a factor of four. Additionally the centres of these high infall-rate haloes provide ideal environments in which to grow pre-existing black holes. Further research into the (supermassive) star formation dynamics of rapidly collapsing haloes, with inhomogeneous metal distributions, is required to gain more insight into both supermassive star formation in early galaxies as well as early black hole growth.}, author = {Regan, John A. and Haiman, Zoltán and Wise, John H. and O'Shea, Brian W. and Norman, Michael L.}, issn = {2565-6120}, journal = {The Open Journal of Astrophysics}, number = {1}, publisher = {Maynooth University}, title = {{Massive star formation in metal-enriched haloes at high redshift}}, doi = {10.21105/astro.2006.14625}, volume = {3}, year = {2020}, } @article{17579, abstract = {Approximately 200 supermassive black holes (SMBHs) have been discovered within the first ∼gigayear after the Big Bang. One pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs). A possible obstacle to this scenario is that the collapsing gas fragments and forms a cluster of main-sequence stars. Here, we raise the possibility that stellar collisions may be sufficiently frequent and energetic to inhibit the contraction of the massive protostar, avoiding strong UV radiation driven outflows, and allowing it to continue growing into an SMS. We investigate this scenario with semianalytic models incorporating star formation; gas accretion; dynamical friction from stars and gas; stellar collisions; and gas ejection. We find that when the collapsing gas fragments at a density of ≲3 × 1010 cm−3, the central protostar contracts due to infrequent stellar mergers, and in turn photoevaporates the remaining collapsing gas, resulting in the formation of a ≲104 M⊙ object. On the other hand, when the collapsing gas fragments at higher densities (expected for a metal-poor cloud with Z ≲ 10−5 Z⊙ with suppressed H2 abundance) the central protostar avoids contraction and keeps growing via frequent stellar mergers, reaching masses as high as ∼105–106 M⊙. We conclude that frequent stellar mergers represent a possible pathway to form massive BHs in the early universe.}, author = {Tagawa, Hiromichi and Haiman, Zoltán and Kocsis, Bence}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, publisher = {American Astronomical Society}, title = {{Making a supermassive star by stellar bombardment}}, doi = {10.3847/1538-4357/ab7922}, volume = {892}, year = {2020}, } @article{17581, abstract = {We present analysis of Chandra X-ray observations of seven quasars that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on the apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs, including harder or softer X-ray spectra, ripple-like profiles in the Fe K-α line, and distinct peaks in the spectrum due to the separation of the accretion disk into a circumbinary disk and mini disks around each SMBH. We obtained Chandra observations to test these models and assess whether these quasars could contain binary SMBHs. We instead find that the quasar spectra are all well fit by simple absorbed power-law models, with the rest-frame 2–10 keV photon indices, Γ, and the X-ray-to-optical power slopes, αOX, indistinguishable from those of the larger quasar population. This may indicate that these seven quasars are not truly subparsec binary SMBH systems, or it may simply reflect that our sample size was too small to robustly detect any differences. Alternatively, the X-ray spectral changes might only be evident at energies higher than probed by Chandra. Given the available models and current data, no firm conclusions are drawn. These observations will help motivate and direct further work on theoretical models of binary SMBH systems, such as modeling systems with thinner accretion disks and larger binary separations.}, author = {Saade, M. Lynne and Stern, Daniel and Brightman, Murray and Haiman, Zoltán and Djorgovski, S. G. and D’Orazio, Daniel and Ford, K. E. S. and Graham, Matthew J. and Jun, Hyunsung D. and Kraft, Ralph P. and McKernan, Barry and Vikhlinin, Alexei and Walton, Dominic J.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, publisher = {American Astronomical Society}, title = {{Chandra observations of candidate subparsec binary supermassive black holes}}, doi = {10.3847/1538-4357/abad31}, volume = {900}, year = {2020}, } @article{17587, abstract = {The astrophysical origin of gravitational wave (GW) events discovered by LIGO/VIRGO remains an outstanding puzzle. In active galactic nuclei (AGNs), compact-object binaries form, evolve, and interact with a dense star cluster and a gas disk. An important question is whether and how binaries merge in these environments. To address this question, we have performed one-dimensional N-body simulations combined with a semianalytical model that includes the formation, disruption, and evolution of binaries self-consistently. We point out that binaries can form in single–single interactions through the dissipation of kinetic energy in a gaseous medium. This "gas-capture" binary formation channel contributes up to 97% of gas-driven mergers and leads to a high merger rate in AGN disks even without preexisting binaries. We find the merger rate to be in the range of ∼0.02–60 Gpc−3 yr−1. The results are insensitive to the assumptions on the gaseous hardening processes: we find that once they are formed, binaries merge efficiently via binary–single interactions even if these gaseous processes are ignored. We find that the average number of mergers per black hole (BH) is 0.4, and the probability for repeated mergers in 30 Myr is ∼0.21–0.45. High BH masses due to repeated mergers, high eccentricities, and a significant Doppler drift of GWs are promising signatures that distinguish this merger channel from others. Furthermore, we find that gas-capture binaries reproduce the distribution of low-mass X-ray binaries in the Galactic center, including an outer cutoff at ∼1 pc due to the competition between migration and hardening by gas torques.}, author = {Tagawa, Hiromichi and Haiman, Zoltán and Kocsis, Bence}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, publisher = {American Astronomical Society}, title = {{Formation and evolution of compact-object binaries in AGN disks}}, doi = {10.3847/1538-4357/ab9b8c}, volume = {898}, year = {2020}, } @article{17591, abstract = {The rotational kinematic Sunyaev-Zeldovich (rkSZ) signal, imprinted on the cosmic microwave background (CMB) by the gaseous halos (spinning “atmospheres”) of foreground galaxies, would be a novel probe of galaxy formation. Although the signal is too weak to detect in individual galaxies, we analyze the feasibility of its statistical detection via stacking CMB data on many galaxies for which the spin orientation can be estimated spectroscopically. We use an “optimistic” model, in which fully ionized atmospheres contain the cosmic baryon fraction and spin at the halo’s circular velocity 𝑣circ, and a more realistic model, based on hydrodynamical simulations, with multiphase atmospheres spinning at a fraction of 𝑣circ. We incorporate realistic noise estimates into our analysis. Using low-redshift galaxy properties from the MaNGA spectroscopic survey (with median halo mass of 6.6×1011  𝑀⊙), and CMB data quality from Planck, we find that a 3⁢𝜎 detection would require a few×104 galaxies, even in the optimistic model. This is too high for current surveys, but upcoming higher-angular resolution CMB experiments will significantly reduce the requirements: stacking CMB data on galaxy spins in a ∼10 deg2 can rule out the optimistic models, and ≈350  deg2 will suffice for a 3⁢𝜎 detection with ACT. As a proof-of-concept, we stacked Planck data on the position of ≈2,000 MaNGA galaxies, aligned with the galaxies’ projected spin, and scaled to their halos’ angular size. We rule out average temperature dipoles larger than ≈1.9  𝜇⁢K around field spiral galaxies.}, author = {Matilla, José Manuel Zorrilla and Haiman, Zoltán}, issn = {2470-0010}, journal = {Physical Review D}, number = {8}, publisher = {American Physical Society}, title = {{Probing gaseous galactic halos through the rotational kinematic Sunyaev-Zeldovich effect}}, doi = {10.1103/physrevd.101.083016}, volume = {101}, year = {2020}, } @article{17595, abstract = {We study the thermal evolution of UV-irradiated atomic cooling haloes using high-resolution three-dimensional hydrodynamic simulations. We consider the effect of H− photodetachment by Lyα cooling radiation trapped in the optically-thick cores of three such haloes, a process that has not been included in previous simulations. Because H− is a precursor of molecular hydrogen, its destruction can diminish the H2 abundance and cooling. We find that the critical UV flux for suppressing H2-cooling is decreased by ∼15–50 per cent in our fiducial models. Previous one-zone modelling found a larger effect, with Jcrit reduced by a factor of a few; we show that adopting a constant halo mass to determine the trapped Lyα energy density, as is done in the one-zone models, yields a larger reduction in Jcrit, consistent with their findings. Our results nevertheless suggest that Lyα radiation may have an important effect on the thermal evolution of UV-irradiated haloes, and therefore on the potential for massive black hole formation.}, author = {Wolcott-Green, Jemma and Haiman, Zoltán and Bryan, Greg L}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {138--144}, publisher = {Oxford University Press}, title = {{Suppression of H2 cooling in protogalaxies aided by trapped Lyα cooling radiation}}, doi = {10.1093/mnras/staa3057}, volume = {500}, year = {2020}, } @article{17596, abstract = {Binary black hole mergers encode information about their environment and the astrophysical processes that led to their formation. Measuring the redshift dependence of their merger rate will help probe the formation and evolution of galaxies and the evolution of the star formation rate. Here we compute the cosmic evolution of the merger rate for stellar-mass binaries in the disks of active galactic nuclei (AGNs). We focus on recent evolution out to redshift z = 2, covering the accessible range of current Earth-based gravitational-wave observatories. On this scale, the AGN population density is the main contributor to redshift dependence. We find that the AGN-assisted merger rate varies by less than a factor of two in the range 0 < z ≤ 2, comparable to the expected level of evolution for globular clusters, but much smaller than the order-of-magnitude evolution for field binaries.}, author = {Yang, Y. and Bartos, I. and Haiman, Zoltán and Kocsis, B. and Márka, S. and Tagawa, H.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, publisher = {American Astronomical Society}, title = {{Cosmic evolution of stellar-mass black hole merger rate in active galactic nuclei}}, doi = {10.3847/1538-4357/ab91b4}, volume = {896}, year = {2020}, }