@article{
 title = {Prospects of gravitational-waves detections from common-envelope evolution with LISA},
 type = {article},
 year = {2021},
 websites = {http://arxiv.org/abs/2102.00078},
 month = {1},
 day = {29},
 id = {4a99bd3a-a02a-3462-9890-edfc8dd6d35d},
 created = {2021-02-02T10:21:47.016Z},
 accessed = {2021-02-02},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-02-09T13:43:05.847Z},
 read = {true},
 starred = {false},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 private_publication = {false},
 abstract = {Understanding common envelope (CE) evolution is an outstanding problem in binary evolution. Although the CE phase is not driven by gravitational-wave (GW) emission, the in-spiraling binary emits GWs that passively trace the CE dynamics. Detecting this GW signal would provide direct insight into the gas-driven physics. Even a non-detection might offer invaluable constraints. We investigate the prospects of detection of a Galactic CE by LISA. While the dynamical phase of the CE is likely sufficiently loud for detection, it is short and thus rare. We focus instead on the self-regulated phase that proceeds on a thermal timescale. Based on population synthesis calculations and the (unknown) signal duration in the LISA band, we expect $\sim 0.1-100$ sources in the Galaxy during the mission duration. We map the GW observable parameter space of frequency $f_\mathrmGW$ and its derivative $\dot f_\mathrmGW$ remaining agnostic on the specifics of the inspiral, and find that signals with $\mathrmSNR>10$ are possible if the CE stalls at separations such that $f_\mathrmGW\gtrsim2\times10^-3\,\mathrmHz$. We investigate the possibility of misidentifying the signal with other known sources. If the second derivative $\ddot f_\mathrmGW$ can also be measured, the signal can be distinguished from other sources using a GW braking-index. Alternatively, coupling LISA with electromagnetic observations of peculiar red giant stars and/or infrared and optical transients might allow for the disentangling of a Galactic CE from other Galactic and extra-galactic GW sources.},
 bibtype = {article},
 author = {Renzo, M. and Callister, T. and Chatziioannou, K. and van Son, L. A. C. and Mingarelli, C. M. F. and Cantiello, M. and Ford, K. E. S. and McKernan, B. and Ashton, G.}
}

Understanding common envelope (CE) evolution is an outstanding problem in binary evolution. Although the CE phase is not driven by gravitational-wave (GW) emission, the in-spiraling binary emits GWs that passively trace the CE dynamics. Detecting this GW signal would provide direct insight into the gas-driven physics. Even a non-detection might offer invaluable constraints. We investigate the prospects of detection of a Galactic CE by LISA. While the dynamical phase of the CE is likely sufficiently loud for detection, it is short and thus rare. We focus instead on the self-regulated phase that proceeds on a thermal timescale. Based on population synthesis calculations and the (unknown) signal duration in the LISA band, we expect $\sim 0.1-100$ sources in the Galaxy during the mission duration. We map the GW observable parameter space of frequency $f_\mathrmGW$ and its derivative $\dot f_\mathrmGW$ remaining agnostic on the specifics of the inspiral, and find that signals with $\mathrmSNR>10$ are possible if the CE stalls at separations such that $f_\mathrmGW\gtrsim2\times10^-3\,\mathrmHz$. We investigate the possibility of misidentifying the signal with other known sources. If the second derivative $\ddot f_\mathrmGW$ can also be measured, the signal can be distinguished from other sources using a GW braking-index. Alternatively, coupling LISA with electromagnetic observations of peculiar red giant stars and/or infrared and optical transients might allow for the disentangling of a Galactic CE from other Galactic and extra-galactic GW sources.

@article{
 title = {Rapid stellar and binary population synthesis with COMPAS},
 type = {article},
 year = {2021},
 websites = {http://arxiv.org/abs/2109.10352},
 month = {9},
 day = {20},
 id = {6550303c-68c5-3eb4-bce1-b3e3e75efaf1},
 created = {2021-09-24T15:47:24.633Z},
 accessed = {2021-09-24},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2022-03-04T17:05:49.424Z},
 read = {true},
 starred = {true},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 private_publication = {false},
 abstract = {Compact Object Mergers: Population Astrophysics and Statistics (COMPAS; https://compas.science ) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parameterized assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the GitHub repository https://github.com/TeamCOMPAS/COMPAS/ , and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document that will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.},
 bibtype = {article},
 author = {COMPAS, Team and :, undefined and Riley, Jeff and Agrawal, Poojan and Barrett, Jim W. and Boyett, Kristan N. K. and Broekgaarden, Floor S. and Chattopadhyay, Debatri and Gaebel, Sebastian M. and Gittins, Fabian and Hirai, Ryosuke and Howitt, George and Justham, Stephen and Khandelwal, Lokesh and Kummer, Floris and Lau, Mike Y. M. and Mandel, Ilya and de Mink, Selma E. and Neijssel, Coenraad and Riley, Tim and van Son, Lieke and Stevenson, Simon and Vigna-Gomez, Alejandro and Vinciguerra, Serena and Wagg, Tom and Willcox, Reinhold},
 doi = {10.3847/1538-4365/ac416c}
}

Compact Object Mergers: Population Astrophysics and Statistics (COMPAS; https://compas.science ) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parameterized assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the GitHub repository https://github.com/TeamCOMPAS/COMPAS/ , and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document that will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.

@article{
 title = {The redshift evolution of the binary black hole merger rate: a weighty matter},
 type = {article},
 year = {2021},
 websites = {https://arxiv.org/abs/2110.01634,http://arxiv.org/abs/2110.01634},
 month = {10},
 day = {4},
 id = {64baeb4d-354b-381d-8592-ca42b6a84238},
 created = {2021-10-06T13:39:46.050Z},
 accessed = {2021-10-06},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-11-26T12:36:44.379Z},
 read = {true},
 starred = {false},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 private_publication = {false},
 abstract = {Gravitational wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate, $R_\mathrmBBH(z)$. We make predictions for $R_\mathrmBBH(z)$ as a function of black hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations, COMPAS. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterised by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about $30\rmM_\odot$ and short delay times ($t_\rm delay \lesssim 1$Gyr), while the stable RLOF channel primarily forms systems with BH masses above $30\rmM_\odot$ and long delay times ($t_\rm delay \gtrsim 1$Gyr). We provide a new fit for the metallicity specific star-formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction of $R_\mathrmBBH(z)$. This leads to a distinct redshift evolution of $R_\mathrmBBH(z)$ for high and low primary BH masses. We furthermore find that, at high redshift, $R_\mathrmBBH(z)$ is dominated by the CE channel, while at low redshift it contains a large contribution ($\sim 40\%$) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above $30\rmM_\odot$ will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution of $R_\mathrmBBH(z)$ for different BH masses can be tested with future detectors.},
 bibtype = {article},
 author = {van Son, L. A. C. and de Mink, S. E. and Callister, T. and Justham, S. and Renzo, M. and Wagg, T. and Broekgaarden, F. S. and Kummer, F. and Pakmor, R. and Mandel, I.}
}

Gravitational wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate, $R_\mathrmBBH(z)$. We make predictions for $R_\mathrmBBH(z)$ as a function of black hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations, COMPAS. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterised by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about $30\rmM_\odot$ and short delay times ($t_\rm delay \lesssim 1$Gyr), while the stable RLOF channel primarily forms systems with BH masses above $30\rmM_\odot$ and long delay times ($t_\rm delay \gtrsim 1$Gyr). We provide a new fit for the metallicity specific star-formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction of $R_\mathrmBBH(z)$. This leads to a distinct redshift evolution of $R_\mathrmBBH(z)$ for high and low primary BH masses. We furthermore find that, at high redshift, $R_\mathrmBBH(z)$ is dominated by the CE channel, while at low redshift it contains a large contribution ($\sim 40\%$) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above $30\rmM_\odot$ will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution of $R_\mathrmBBH(z)$ for different BH masses can be tested with future detectors.

@article{
 title = {Evidence from Disrupted Halo Dwarfs that $r$-process Enrichment via Neutron Star Mergers is Delayed by $\gtrsim500$ Myrs},
 type = {article},
 year = {2021},
 websites = {http://arxiv.org/abs/2110.14652},
 month = {10},
 day = {27},
 id = {94681577-f5c8-3615-97f7-7d8bfb3f52fc},
 created = {2021-11-05T20:41:12.107Z},
 accessed = {2021-11-05},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-11-05T20:42:37.776Z},
 read = {false},
 starred = {false},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 private_publication = {false},
 abstract = {The astrophysical origins of $r$-process elements remain elusive. Neutron star mergers (NSMs) and special classes of core-collapse supernovae (rCCSNe) are leading candidates. Due to these channels' distinct characteristic timescales (rCCSNe: prompt, NSMs: delayed), measuring $r$-process enrichment in galaxies of similar mass, but differing star-formation durations might prove informative. Two recently discovered disrupted dwarfs in the Milky Way's stellar halo, Kraken and \textitGaia-Sausage Enceladus (GSE), afford precisely this opportunity: both have $M_\star\approx10^8M_\rm\odot$, but differing star-formation durations of $\approx2$ Gyrs and $\approx3.6$ Gyrs. Here we present $R\approx50,000$ Magellan/MIKE spectroscopy for 31 stars from these systems, detecting the $r$-process element Eu in all stars. Stars from both systems have similar [Mg/H]$\approx-1$, but Kraken has a median [Eu/Mg]$\approx-0.1$ while GSE has an elevated [Eu/Mg]$\approx0.2$. With simple models we argue NSM enrichment must be delayed by $500-1000$ Myrs to produce this difference. rCCSNe must also contribute, especially at early epochs, otherwise stars formed during the delay period would be Eu-free. In this picture, rCCSNe account for $\approx50\%$ of the Eu in Kraken, $\approx25\%$ in GSE, and $\approx15\%$ in dwarfs with extended star-formation durations like Sagittarius. The inferred delay time for NSM enrichment is $10-100\times$ longer than merger delay times from stellar population synthesis -- this is not necessarily surprising because the enrichment delay includes time taken for NSM ejecta to be incorporated into subsequent generations of stars. For example, this may be due to natal kicks that result in $r$-enriched material deposited far from star-forming gas, which then takes $\approx10^8-10^9$ years to cool in these galaxies.},
 bibtype = {article},
 author = {Naidu, Rohan P. and Ji, Alexander P. and Conroy, Charlie and Bonaca, Ana and Ting, Yuan-Sen and Zaritsky, Dennis and van Son, Lieke A. C. and Broekgaarden, Floor S. and Tacchella, Sandro and Chandra, Vedant and Caldwell, Nelson and Cargile, Phillip and Speagle, Joshua S.}
}

The astrophysical origins of $r$-process elements remain elusive. Neutron star mergers (NSMs) and special classes of core-collapse supernovae (rCCSNe) are leading candidates. Due to these channels' distinct characteristic timescales (rCCSNe: prompt, NSMs: delayed), measuring $r$-process enrichment in galaxies of similar mass, but differing star-formation durations might prove informative. Two recently discovered disrupted dwarfs in the Milky Way's stellar halo, Kraken and \textitGaia-Sausage Enceladus (GSE), afford precisely this opportunity: both have $M_\star\approx10^8M_\rm\odot$, but differing star-formation durations of $\approx2$ Gyrs and $\approx3.6$ Gyrs. Here we present $R\approx50,000$ Magellan/MIKE spectroscopy for 31 stars from these systems, detecting the $r$-process element Eu in all stars. Stars from both systems have similar [Mg/H]$\approx-1$, but Kraken has a median [Eu/Mg]$\approx-0.1$ while GSE has an elevated [Eu/Mg]$\approx0.2$. With simple models we argue NSM enrichment must be delayed by $500-1000$ Myrs to produce this difference. rCCSNe must also contribute, especially at early epochs, otherwise stars formed during the delay period would be Eu-free. In this picture, rCCSNe account for $\approx50\%$ of the Eu in Kraken, $\approx25\%$ in GSE, and $\approx15\%$ in dwarfs with extended star-formation durations like Sagittarius. The inferred delay time for NSM enrichment is $10-100\times$ longer than merger delay times from stellar population synthesis -- this is not necessarily surprising because the enrichment delay includes time taken for NSM ejecta to be incorporated into subsequent generations of stars. For example, this may be due to natal kicks that result in $r$-enriched material deposited far from star-forming gas, which then takes $\approx10^8-10^9$ years to cool in these galaxies.

@article{
 title = {Gravitational wave sources in our Galactic backyard: Predictions for BHBH, BHNS and NSNS binaries detectable with LISA},
 type = {article},
 year = {2021},
 websites = {http://arxiv.org/abs/2111.13704},
 month = {11},
 day = {26},
 id = {7d07928c-0cdd-3ffd-baf6-0169e6aba357},
 created = {2021-11-30T13:24:09.649Z},
 accessed = {2021-11-30},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-12-01T13:21:49.439Z},
 read = {false},
 starred = {false},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 private_publication = {false},
 abstract = {Future searches for gravitational waves from space will be sensitive to double compact objects (DCOs) in our Milky Way. We present new simulations of the populations of double black holes (BHBHs), black hole neutron stars (BHNSs) and double neutron stars (NSNSs) that will be detectable by the planned space-based gravitational wave detector LISA. For our estimates, we use an empirically-informed model of the metallicity dependent star formation history of the Milky Way. We populate it using an extensive suite of binary population-synthesis predictions for varying assumptions relating to mass transfer, common-envelope, supernova kicks, remnant masses and wind mass loss physics. For a 4(10)-year LISA mission, we predict between 30-370(50-550) detections over these variations, out of which 6-154(9-238) are BHBHs, 2-198(3-289) are BHNSs and 3-35(4-57) are NSNSs. We discuss how the variations in the physics assumptions alter the distribution of properties of the detectable systems, even when the detection rates are unchanged. In particular we discuss the observable characteristics such as the chirp mass, eccentricity and sky localisation and how the BHBH, BHNS and NSNS populations can be distinguished, both from each other and from the more numerous double white dwarf population. We further discuss the possibility of multi-messenger observations of pulsar populations with the Square Kilometre Array (SKA) and assess the benefits of extending the LISA mission.},
 bibtype = {article},
 author = {Wagg, Tom and Broekgaarden, Floor S. and de Mink, Selma E. and van Son, Lieke A. C. and Frankel, Neige and Justham, Stephen}
}

Future searches for gravitational waves from space will be sensitive to double compact objects (DCOs) in our Milky Way. We present new simulations of the populations of double black holes (BHBHs), black hole neutron stars (BHNSs) and double neutron stars (NSNSs) that will be detectable by the planned space-based gravitational wave detector LISA. For our estimates, we use an empirically-informed model of the metallicity dependent star formation history of the Milky Way. We populate it using an extensive suite of binary population-synthesis predictions for varying assumptions relating to mass transfer, common-envelope, supernova kicks, remnant masses and wind mass loss physics. For a 4(10)-year LISA mission, we predict between 30-370(50-550) detections over these variations, out of which 6-154(9-238) are BHBHs, 2-198(3-289) are BHNSs and 3-35(4-57) are NSNSs. We discuss how the variations in the physics assumptions alter the distribution of properties of the detectable systems, even when the detection rates are unchanged. In particular we discuss the observable characteristics such as the chirp mass, eccentricity and sky localisation and how the BHBH, BHNS and NSNS populations can be distinguished, both from each other and from the more numerous double white dwarf population. We further discuss the possibility of multi-messenger observations of pulsar populations with the Square Kilometre Array (SKA) and assess the benefits of extending the LISA mission.

@article{
 title = {Successful Common Envelope Ejection and Binary Neutron Star Formation in 3D Hydrodynamics},
 type = {article},
 year = {2020},
 websites = {http://arxiv.org/abs/2011.06630},
 month = {11},
 day = {12},
 id = {6c961088-d73a-33bd-9d79-fd2f72428f0b},
 created = {2020-11-16T14:09:09.090Z},
 accessed = {2020-11-16},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-01-31T17:07:26.078Z},
 read = {true},
 starred = {false},
 authored = {true},
 confirmed = {false},
 hidden = {false},
 folder_uuids = {90b2a8a7-4864-4c54-a93a-09a09fef7c31},
 private_publication = {false},
 abstract = {The coalescence of two neutron stars was recently observed in a multi-messenger detection of gravitational wave (GW) and electromagnetic (EM) radiation. Binary neutron stars that merge within a Hubble time, as well as many other compact binaries, are expected to form via common envelope evolution. Yet five decades of research on common envelope evolution have not yet resulted in a satisfactory understanding of the multi-spatial multi-timescale evolution for the systems that lead to compact binaries. In this paper, we report on the first successful simulations of common envelope ejection leading to binary neutron star formation in 3D hydrodynamics. We simulate the dynamical inspiral phase of the interaction between a 12$M_\odot$ red supergiant and a 1.4$M_\odot$ neutron star for different initial separations and initial conditions. For all of our simulations, we find complete envelope ejection and a final orbital separation of $\approx 1.1$-$2.8 R_\odot$, leading to a binary neutron star that will merge within 0.01-1 Gyr. We find an $\alpha_\rm CE$-equivalent efficiency of $\approx 0.1$-$0.4$ for the models we study, but this may be specific for these extended progenitors. We fully resolve the core of the star to $\lesssim 0.005 R_\odot$ and our 3D hydrodynamics simulations are informed by an adjusted 1D analytic energy formalism and a 2D kinematics study in order to overcome the prohibitive computational cost of simulating these systems. The framework we develop in this paper can be used to simulate a wide variety of interactions between stars, from stellar mergers to common envelope episodes leading to GW sources.},
 bibtype = {article},
 author = {Law-Smith, Jamie A. P. and Everson, Rosa Wallace and Ramirez-Ruiz, Enrico and de Mink, Selma E. and van Son, Lieke A. C. and Götberg, Ylva and Zellmann, Stefan and Vigna-Gómez, Alejandro and Renzo, Mathieu and Wu, Samantha and Schrøder, Sophie L. and Foley, Ryan J. and Hutchinson-Smith, Tenley}
}

The coalescence of two neutron stars was recently observed in a multi-messenger detection of gravitational wave (GW) and electromagnetic (EM) radiation. Binary neutron stars that merge within a Hubble time, as well as many other compact binaries, are expected to form via common envelope evolution. Yet five decades of research on common envelope evolution have not yet resulted in a satisfactory understanding of the multi-spatial multi-timescale evolution for the systems that lead to compact binaries. In this paper, we report on the first successful simulations of common envelope ejection leading to binary neutron star formation in 3D hydrodynamics. We simulate the dynamical inspiral phase of the interaction between a 12$M_\odot$ red supergiant and a 1.4$M_\odot$ neutron star for different initial separations and initial conditions. For all of our simulations, we find complete envelope ejection and a final orbital separation of $\approx 1.1$-$2.8 R_\odot$, leading to a binary neutron star that will merge within 0.01-1 Gyr. We find an $\alpha_\rm CE$-equivalent efficiency of $\approx 0.1$-$0.4$ for the models we study, but this may be specific for these extended progenitors. We fully resolve the core of the star to $\lesssim 0.005 R_\odot$ and our 3D hydrodynamics simulations are informed by an adjusted 1D analytic energy formalism and a 2D kinematics study in order to overcome the prohibitive computational cost of simulating these systems. The framework we develop in this paper can be used to simulate a wide variety of interactions between stars, from stellar mergers to common envelope episodes leading to GW sources.

@article{
 title = {Polluting the Pair-instability Mass Gap for Binary Black Holes through Super-Eddington Accretion in Isolated Binaries},
 type = {article},
 year = {2020},
 keywords = {Accretion,Binary black holes,Eddington limit,Gravitational wave sources,Pair-instability},
 pages = {100},
 volume = {897},
 websites = {https://iopscience.iop.org/article/10.3847/1538-4357/ab9809},
 month = {7},
 publisher = {arXiv},
 day = {7},
 id = {dd48f191-f8a3-360d-8bed-68ed6a9a0397},
 created = {2021-01-31T16:44:23.849Z},
 accessed = {2020-05-21},
 file_attached = {false},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-03-10T12:41:34.490Z},
 read = {true},
 starred = {true},
 authored = {true},
 confirmed = {true},
 hidden = {false},
 folder_uuids = {90b2a8a7-4864-4c54-a93a-09a09fef7c31,c7b399c6-10ad-492c-9c98-b723817d125a},
 private_publication = {false},
 abstract = {The theory for single stellar evolution predicts a gap in the mass distribution of black holes (BHs) between approximately 45-130M⊙, the so-called "pair-instability mass gap". We examine whether BHs can pollute the gap after accreting from a stellar companion. To this end, we simulate the evolution of isolated binaries using a population synthesis code, where we allow for super-Eddington accretion. Under our most extreme assumptions, we find that at most about 2% of all merging binary BH systems contains a BH with a mass in the pair-instability mass gap, and we find that less than 0.5% of the merging systems has a total mass larger than 90 M⊙. We find no merging binary BH systems with a total mass exceeding 100 M⊙. We compare our results to predictions from several dynamical pathways to pair-instability mass gap events and discuss the distinguishable features. We conclude that the classical isolated binary formation scenario will not significantly contribute to the pollution of the pair-instability mass gap. The robustness of the predicted mass gap for the isolated binary channel is promising for the prospective of placing constraints on (i) the relative contribution of different formation channels, (ii) the physics of the progenitors including nuclear reaction rates, and (iii), tentatively, the Hubble parameter.},
 bibtype = {article},
 author = {van Son, L. A. C. and De Mink, S. E. and Broekgaarden, F. S. and Renzo, M. and Justham, S. and Laplace, E. and Morán-Fraile, J. and Hendriks, D. D. and Farmer, R.},
 doi = {10.3847/1538-4357/ab9809},
 journal = {The Astrophysical Journal},
 number = {1}
}

The theory for single stellar evolution predicts a gap in the mass distribution of black holes (BHs) between approximately 45-130M⊙, the so-called "pair-instability mass gap". We examine whether BHs can pollute the gap after accreting from a stellar companion. To this end, we simulate the evolution of isolated binaries using a population synthesis code, where we allow for super-Eddington accretion. Under our most extreme assumptions, we find that at most about 2% of all merging binary BH systems contains a BH with a mass in the pair-instability mass gap, and we find that less than 0.5% of the merging systems has a total mass larger than 90 M⊙. We find no merging binary BH systems with a total mass exceeding 100 M⊙. We compare our results to predictions from several dynamical pathways to pair-instability mass gap events and discuss the distinguishable features. We conclude that the classical isolated binary formation scenario will not significantly contribute to the pollution of the pair-instability mass gap. The robustness of the predicted mass gap for the isolated binary channel is promising for the prospective of placing constraints on (i) the relative contribution of different formation channels, (ii) the physics of the progenitors including nuclear reaction rates, and (iii), tentatively, the Hubble parameter.

@article{
 title = {Galaxies with monstrous black holes in galaxy cluster environments},
 type = {article},
 year = {2019},
 keywords = {galaxies: evolution,galaxies: formation,galaxies: interactions},
 pages = {396-407},
 volume = {485},
 websites = {https://academic.oup.com/mnras/article/485/1/396/5315788},
 month = {5},
 day = {1},
 id = {1d8c3c54-7c59-3c03-8a33-053e928b74a8},
 created = {2020-05-21T13:42:21.691Z},
 accessed = {2020-05-21},
 file_attached = {true},
 profile_id = {7b3f4dc1-fa9b-3ee3-9b44-e1033c3fb950},
 last_modified = {2021-01-31T17:17:23.841Z},
 read = {false},
 starred = {false},
 authored = {true},
 confirmed = {true},
 hidden = {false},
 folder_uuids = {90b2a8a7-4864-4c54-a93a-09a09fef7c31},
 private_publication = {false},
 abstract = {Massive early-type galaxies follow a tight relation between the mass of their central supermassive black hole (MBH) and their stellar mass (M∗). The origin of observed positive outliers from this relation with extremely high MBH (> 109M⊙) remains unclear. We present a study of such outliers in the Hydrangea/C-EAGLE cosmological hydrodynamical simulations, designed to enable the study of high-mass galaxy formation and evolution in cluster environments. We find 69 MBH(M∗) outliers at z=0, defined as those with MBH107M⊙ and MBH/M∗ > 0.01. This paper focuses on a sample of five extreme outliers, that have been selected based on their MBH and M∗ values, which are comparable to the most recent estimates of observed positive outliers. This sample of five outliers, classified as 'black hole monster galaxies' (BMGs), was traced back in time to study their origin and evolution. In agreement with the results of previous simulations for lower mass MBH(M∗) outliers, we find that these galaxies became outliers due to a combination of their early formation times and tidal stripping. For BMGs with MBH 109 M⊙, major mergers (with a stellar mass ratio of μ > 0.25) at early times (z> 2) precede the rapid growth of their supermassive BHs. Furthermore, the scatter in the relation between MBH and stellar velocity dispersion, σ, correlates positively with the scatter in [Mg/Fe](σ). This indicates that the alpha enhancement of these galaxies, which is closely related to their star formation history, is related to the growth of their central BHs.},
 bibtype = {article},
 author = {van Son, Lieke A C and Barber, Christopher and Bahé, Yannick M. and Schaye, Joop and Barnes, David J. and Crain, Robert A. and Kay, Scott T. and Theuns, Tom and Dalla Vecchia, Claudio},
 doi = {10.1093/mnras/stz399},
 journal = {Monthly Notices of the Royal Astronomical Society},
 number = {1}
}

Massive early-type galaxies follow a tight relation between the mass of their central supermassive black hole (MBH) and their stellar mass (M∗). The origin of observed positive outliers from this relation with extremely high MBH (> 109M⊙) remains unclear. We present a study of such outliers in the Hydrangea/C-EAGLE cosmological hydrodynamical simulations, designed to enable the study of high-mass galaxy formation and evolution in cluster environments. We find 69 MBH(M∗) outliers at z=0, defined as those with MBH107M⊙ and MBH/M∗ > 0.01. This paper focuses on a sample of five extreme outliers, that have been selected based on their MBH and M∗ values, which are comparable to the most recent estimates of observed positive outliers. This sample of five outliers, classified as 'black hole monster galaxies' (BMGs), was traced back in time to study their origin and evolution. In agreement with the results of previous simulations for lower mass MBH(M∗) outliers, we find that these galaxies became outliers due to a combination of their early formation times and tidal stripping. For BMGs with MBH 109 M⊙, major mergers (with a stellar mass ratio of μ > 0.25) at early times (z> 2) precede the rapid growth of their supermassive BHs. Furthermore, the scatter in the relation between MBH and stellar velocity dispersion, σ, correlates positively with the scatter in [Mg/Fe](σ). This indicates that the alpha enhancement of these galaxies, which is closely related to their star formation history, is related to the growth of their central BHs.