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online talks
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Wednesday 13/09
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9:5010:02AlexRawlingsThe stochastic nature of SMBH binary eccentricityWe present a study of the stochasticity of supermassive black hole (SMBH) binary eccentricity in N-body simulations of equal-mass galaxy mergers using the Ketju code and its dependency on the deflection angle before a bound binary is formed. The effect of parsec-scale variation in the impact parameter, and its connection to orbital uncertainty in the real Universe, is discussed.
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10:0210:14DavidIzquierdo-VillalbaProperties and merger signatures of galaxies hosting LISA coalescing massive black hole binariesThe gravitational wave (GW) antenna LISA will detect the signal from coalescing massive black hole binaries (MBHBs) of $\rm 10^4\,{-}\,10^7\, \msun{}$, providing clues on their formation and growth along cosmic history. Some of these events will be localized with a precision of several to less than a deg$^2$, enabling the possible identification of their host galaxy. This work explores the properties of the host galaxies of LISA MBHBs below $z\,{\lesssim}\,3$. We generate a simulated lightcone by using the semi-analytical model \LGalaxies{} applied on the merger trees of the high-resolution N-body cosmological simulation \texttt{Millennium-II}. The model shows that LISA MBHBs are expected to be found in optically dim ($r\,{>}\,20$), star-forming ($\rm sSFR\,{>}\,10^{-10}\, \rm yr^{-1}$), gas-rich ($f_{\rm gas}\,{>}\,0.6$) and disc-dominated ($\rm B/T\,{<}\,0.7$) \textit{low-mass galaxies} of stellar masses $10^8\,{-}\,10^9 \msun{}$. However, these properties are indistinguishable from those of galaxies harboring single massive black holes with comparable mass, making difficult the selection of LISA hosts among the whole population of low-mass galaxies. Motivated by this, we explore the possibility of using merger signatures to select LISA hosts. We find that $40\,{-}\,80$\% of the galaxies housing LISA MBHBs display merger features related to the interaction which brought the secondary MBH to the galaxy. Despite this, around $60\%$ of dwarf galaxies placed in the surroundings of the LISA hosts will show such kind of features as well, challenging the unequivocal detection of LISA hosts through the search of merger signatures. Consequently, the detection of an electromagnetic transient associated with the MBHB merger will be vital to pinpoint the star-forming dwarf galaxy where these binary systems evolve and coalesce.
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10:1410:26Alessia FranchiniPre-merger signatures of massive black hole binaries in gaseous environmentsThe identification of electromagnetic (EM) counterparts to the Gravitational Wave (GW) signals that are expected to be detected by the upcoming Laser Interferometer Space Antenna (LISA) is of fundamental importance to characterize the evolution of Massive Black Hole Binaries (MBHBs) in their environment. Furthermore, EM counterparts complete the multi-messenger picture allowing better sky localization of the GW events. We here study merging equal mass MBHBs embedded in circumbinary discs from separations of 100 Rg down to the merger, following the post merger evolution, with 3D hyper-Lagrangian resolution simulations with the gizmo-MFM code. The binary orbit evolves owing to the presence of the gaseous disc and the addition of 2.5 Post-Newtonian (PN) corrections. We find a drop in X-ray flux by roughly a factor 5, at merger, accompained by a depletion of energy in the UV band that gives a characteristic shape to the spectral energy distribution.
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10:2610:38ValeriyaKorolNeutron Star - White Dwarf Binaries: Probing Natal Kicks and Formation Channels with LISANeutron star-white dwarf (NSWD) binaries detectable with LISA provide a unique opportunity to study a range of phenomena involved in binary evolution, including poorly constrained NS natal kicks. In this talk, I will demonstrate how population synthesis is used to predict the Galactic population of these binaries within LISA's frequency range. I will discuss the challenge of differentiating NSWDs from double white dwarfs at frequencies below 2 mHz, I will present how eccentricity and chirp mass distributions can serve as constraints on models of NS natal kicks and common envelope evolution. Additionally, I will discuss the prospects for identifying NSWDs above the Galactic plane and their potential electromagnetic counterparts in radio.
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11:1511:27MuditGargThe minimum detectable eccentricity in gravitational waves from LISA massive black hole binariesWe explore the eccentricity detection threshold of the future space-based mission LISA for gravitational waves (GWs) radiated by massive black hole binaries (MBHBs) with BH masses in the range ~ 10^4–10^6 MSun at redshift z = 1. We will generate mock high-order post-Newtonian eccentric waveforms, project them in LISA arms to perform time delay interferometry to cancel laser noise, and use both Fisher and Bayesian inference via MCMC to see how well we can constrain injected parameters as a function of the waveform’s signal-to-noise ratio. This study is much needed as eccentricity can be a unique tracer of the environment where these MBHBs evolve to reach the merger phase in the LISA band.
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11:2711:39LucaBroggiDynamics of EMRI formation in nuclear star clustersWe have developed a computationally efficient, two-population, time-dependent Fokker–Plank approach in the two dimensions of energy and angular momentum to study the rates of tidal disruption events (TDEs), extreme mass ratio inspirals (EMRIs), and direct plunges occurring around massive black holes (MBHs) in galactic nuclei. We find that mass segregation and, more in general, the time dependency of the distribution function regulate the event rate: TDEs always decline with time, whereas EMRIs and plunges reach a maximum and undergo a subsequent nearly exponential decay. Once suitably normalized, the rates associated to different choices of MBH mass and galaxy density overlap nearly perfectly. Based on this, we provide a simple scaling that allows to reproduce the time-dependent event rates for any MBH mass and underlying galactic nucleus. Although our peak rates are in general agreement with the literature relying on the steady-state (non-time-dependent) assumption, those can be sustained on a time-scale that strongly depends on the properties of the system. In particular, this can be much shorter than a Gyr for relatively light MBHs residing in dense systems. This warns against using steady-state models to compute global TDE, EMRI, and plunge rates and calls for a more sophisticated, time-dependent treatment of the problem.
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11:3911:51AliceSpadaroGlitch systematics on the observation of massive black-hole binaries with LISADetecting and coherently characterizing thousands of gravitational-wave signals is a core data- analysis challenge for the Laser Interferometer Space Antenna (LISA). Transient artifacts, or “glitches”, with disparate morphologies are expected to be present in the data, potentially affecting the scientific return of the mission. We present the first joint reconstruction of short-lived astrophysical signals and noise artifacts. Our analysis is inspired by glitches observed by the LISA Pathfinder mission, including both acceleration and fast displacement transients. We perform full Bayesian inference using LISA time-delay interferometric data and gravitational waveforms describing mergers of massive black holes. We focus on a representative binary with a detector-frame total mass of 6 × 107M⊙ at redshift 5, yielding a signal lasting ∼ 30 h in the LISA sensitivity band. We explore two glitch models of different flexibility, namely a fixed parametric family and a shapelet decomposition. In the most challenging scenario, we report a complete loss of the gravitational-wave signal if the glitch is ignored; more modest glitches induce biases on the black-hole parameters. On the other hand, a joint inference approach fully sanitizes the reconstruction of both the astrophysical and the glitch signal. We also inject a variety of glitch morphologies in isolation, without a superimposed gravitational signal, and show we can identify the correct transient model. Our analysis is an important stepping stone toward a realistic treatment of LISA data in the context of the highly sought-after “global fit”.
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11:5112:03AlessandroTrincaUnveiling the nature of early black hole seeds with multifrequency gravitational wave observationsUnderstanding the formation and growth of supermassive black holes (SMBHs) at high redshift still represents a major challenge for theoretical models. Despite the latest observational facilities opened to the detection of AGNs shining at increasingly earlier epochs, a deeper understanding of the evolutionary path of the initial SMBH progenitors, also called BH seeds, will be allowed only by the future generation of gravitational waves (GW) interferometers, and especially with the advent of the Laser Interferometer Space Antenna (LISA), which will detect the signal from coalescing massive black hole binaries (MBHBs) of 10^4-10^7 solar masses up to z~20. Within this framework, we use the Cosmic Archaeology Tool, a semi-analytical model that reconstructs the formation and evolution of the first galaxies and AGNs, implementing a detailed modeling of the pairing, hardening and merger timescales of MBHBs to track their evolution and swift transit across the LISA bandwidth as GW sources. In particular, we focus on how different competing channels for the formation of first BH seed and alternative scenarios of BH growth impact on the predicted rate of observable merger events. This enable us to determine how tightly future LISA detections will constrain the dominant mechanisms of BH seed formation and evolution in the early Universe.
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12:0312:15MartinaToscaniGravitational lensing in the context of LISA and space-based detectorsIn this talk, I will describe gravitational lensing applied to sources of interest for LISA and other (possible) space-based detectors. I will mainly focus on lensed estreme mass ratio inspirals (LEMRIs), providing detection rates and parameter estimation of these sources (Toscani et al. 2023b, in progress). Then I will extend the discussion on lensing to the case of tidal disruption events (Toscani et al. 2023) and massive black hole binaries.
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12:1512:27Manuel Arca SeddaThe growth of intermediate-mass black holes in star clustersThe processes that govern the formation of intermediate-mass black holes (IMBHs) in dense stellar clusters are still unclear. Here, we discuss the role of stellar mergers, star-BH interactions and accretion, as well as BH binary (BBH) mergers in seeding and growing IMBHs in the Dragon-II simulation database, a suite of 19 direct N - body models representing dense clusters with up to 10^6 stars. Dragon-II IMBHs have typical masses of mIMBH = (100 − 380) M and relatively large spins χIMBH > 0.6. We find a link between the IMBH formation mechanism and the cluster structure. In clusters denser than 3 × 10^5 Msun pc^−3, the collapse of massive star collision products represents the dominant IMBH formation process, leading to the formation of heavy IMBHs (mIMBH > 200 M ), possibly slowly rotating, that form over times < 5 Myr and grow further via stellar accretion and mergers in just < 30 Myr. BBH mergers are the dominant IMBH formation channel in less dense clusters, for which we find that the looser the cluster, the longer the formation time (10 − 300 Myr) and the larger the IMBH mass, although remaining within 200 M . Strong dynamical scatterings and relativistic recoil efficiently eject all IMBHs in Dragon-II clusters, suggesting that IMBHs in this type of clusters are unlikely to grow beyond a few 10^2 M. According to our models, I will show that LISA could detect N det = 19 BBHs and ∼ 5 IMBH-BH binaries per year.
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Thursday 14/09
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9:309:42Kunyang LiUsing Dual AGNs to Predict the Rate of Black Hole MergersDual active galaxy nuclei (dAGNs) trace the population of post-merger galaxies and are the precursors to massive black hole (MBH) mergers, an important source of gravitational waves that may be observed by LISA. We used the population of nearly 2000 galaxy mergers predicted by the TNG50-3 simulation to seed semi-analytic models of the orbital evolution and coalescence of MBH pairs with initial separations of about 1 kpc. We also calculate the dAGN luminosities and separation of these pairs as they evolve in post-merger galaxies, and show how the coalescence fraction of dAGNs changes with redshift. We present a method to estimate the MBH coalescence rate as well as the potential LISA detection rate given a survey of dAGNs. Comparing these rates to the eventual LISA measurements will help determine the efficiency of dynamical friction in post-merger galaxies.
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9:429:54JoeMcCaffreyBuilding a BH Merger Catalogue using the Renaissance Simulations In this project we will focus on the High resolution, high-z Renaissance Simulations to make predictions on the merger rate of MBHs. As these simulations do not contain a prescription for a central massive black hole seed, we will search for candidate halos in post processing. We seed the halos found in Renaissance based on their inflow rate, compactness and metallicity, to build a number density of seed host halos. After the halos have been seeded, we will track the haloes via merger trees to calculate halo merger rates and hence MBH merger rates (including delay times). We can then use this to build a merger catalog to aid in the observations made by LISA.
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9:5410:06MatteoBoschiniExtending black-hole remnant surrogate models to extreme mass ratiosNumerical-relativity surrogate models for both black-hole merger waveforms and remnants have emerged as important tools in gravitational-wave astronomy. While producing very accurate predictions, their applicability is limited to the region of the parameter space where numerical- relativity simulations are available and computationally feasible. Notably, this excludes extreme mass ratios. We present a machine-learning approach to extend the validity of existing and future numerical-relativity surrogate models toward the test-particle limit, targeting in particular the mass and spin of post-merger black-hole remnants. Our model is trained on both numerical- relativity simulations at comparable masses and analytical predictions at extreme mass ratios. We extend the gaussian-process-regression model NRSur7dq4Remnant, validate its performance via cross validation, and test its accuracy against additional numerical-relativity runs. Our fit, which we dub NRSur7dq4EmriRemnant, reaches an accuracy that is comparable to or higher than that of existing remnant models while providing robust predictions for arbitrary mass ratios.
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10:0610:18ShihongLiaoHydrodynamical galaxy merger simulations with the KETJU codeThe coalescence of massive black hole (BH) binaries during galaxy mergers is of great interest for upcoming low-frequency gravitational wave observatories, including LISA. We have recently incorporated a new model for the accretion and feedback of BH binaries into the KETJU code, enabling us to resolve the evolution of BH binaries down to separations of tens of Schwarzschild radii in gas-rich galaxy mergers. Our subgrid binary accretion model extends the widely used Bondi-Hoyle-Lyttleton accretion into the binary phase and incorporates preferential mass accretion onto the secondary SMBH, guided by results from small-scale hydrodynamical circumbinary disc simulations. Utilizing this new BH accretion and feedback model, we conducted a series of idealized hydrodynamical galaxy merger simulations, including disc-disc and elliptical-elliptical mergers, to investigate BH merger times and the influence of various galaxy formation processes. In this talk, I will present our findings from these KETJU galaxy merger simulations.
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10:1810:30BastiánReinosoSupermassive star formation in the first star clusters: Emergence of massive black hole seedsThe formation of supermassive stars is an essential intermediate-step during the formation of the most massive black hole seeds with 10^4-10^5 MSun. Numerical simulations have shown that this is possible in pristine atomic-cooling halos that grow rapidly via mergers with smaller halos, or in halos irradiated by a nearby star-forming region. In this scenario, all the gas is accreted into a single central object. Although no fragmentation is seen at parsec scales in simulations, this remains uncertain as they cannot resolve the smallest scales. In this talk, I present the results of numerical simulations in which we mimic sub-parsec scale fragmentation during the assembly of supermassive stars in atomic-cooling halos and show that, despite fragmentation, it is still possible to form objects with 10^4 MSun via a combination of gas accretion and stellar collisions.
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10:3010:42MassimoDottiIdentification of LISA MBHB progenitors in electromagnetic surveysI will review the electromagnetic searches of massive black hole binaries performed to date, highlighting the observational bias that led to no binary candidates in the LISA mass range. I will then describe a new and fast method to search for binaries in large multi-epoch spectral databases.
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11:1511:27CarolynDrakeA Preliminary Census of Time-Evolving LISA Error Volumes Utilizing SDSS PhotometrySignals from merging intermediate mass black holes (IMBH) (105 – 107M☉) are outside the detection range of current gravitational wave (GW) observatories, such as pulsar timing arrays or the Laser Interferometer Gravitational-wave Observatory. However, with the launch of the Laser Interferometer Space Antenna (LISA), we will be able to estimate properties of merging IMBH systems, such as sky position, luminosity distance, chirp mass, and mass ratio. Further, LISA’s uncertainties on these estimates will evolve over time such that the process of identifying the source system using electromagnetic (EM) follow up can begin as early as a month from merger. A single coincident EM and GW observation of a LISA merger will not only elucidate the gaseous environment around the black hole binary itself, but will provide two distinctive redshift measurements, creating a unique probe for cosmology and spacetime. In this talk, I present a framework that creates simulated time evolving LISA error volumes based on the uncertainty constraints for sky position and luminosity distance for a variety of systems of different masses and redshifts. I then apply these error volumes to Sloan Digital Sky Survey photometry and perform a census of objects at various times until merger. This is the first time a census of this nature has been done using real astronomical objects and is the first step in creating a process for coincident EM observations of LISA sources. Additionally, I will discuss the work that needs to be accomplished and the questions that need to be addressed prior to LISA’s launch to successfully complete these observations.
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11:2711:39GiuliaFumagalliSpin-eccentricity interplay in merging black holesTo understand the formation channel of black hole binaries, it is crucial to simultaneously measure the orientation of the spins of the black holes and the orbital eccentricity. Due to the emission of gravitational waves, we expect that initially eccentric binaries will reach the merger with an eccentricity lower than what can be measured by gravitational wave detectors. To overcome this problem, we develop a formalism capable of describing the evolution of spinning and eccentric binaries within the framework of the Post-Newtonian regime. We investigate the impact of eccentricity on the evolution of black hole spins, and we propose leveraging this interplay to deduce the eccentricity of binaries.
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11:3911:51FlorentinaPislanThe Impact of Gravitational Waves on Multi-Messenger Analysis of Observed Electromagnetic SourcesAstrophysical events, such as mergers of black holes and neutron stars or strong emitting sources such as pulsars or supernovae, can be better understood when analyzed from multiple perspectives. With the current and upcoming gravitational wave experiments, we expect to add gravitational wave (GW) signals as important messengers for analyzing these kinds of events. In this work, we present our studies on the influence of GW source parameters upon the shape of the waveform and on how we can use these new detected and characterized messengers to improve our knowledge of sources already observed in electromagnetic and with astrophysical particles. We also show the results of our multimessenger analysis on different astrophysical sources such as quasars and X-shaped radio galaxies.
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11:5112:03FedericoPozzoliA new approach to detection and parameter estimation of SGWBs in LISAOne of the primary objectives of the LISA gravitational wave (GW) detector is to detect stochastic gravitational wave foregrounds and backgrounds (henceforth, SGWB), both of astrophyisical and cosmological origin. However, disentangling the different components while taking into account the instrumental noise uncertainty is challenging. In this talk, assuming an accurate LISA response function, we propose an innovative method to search and estimate parameters of SGWB. We apply it to the astrophysical case of a foreground originating from populations of Extreme Mass Ratio Inspirals (EMRIs).
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12:0312:15PeterJohanssonKETJU -resolving small-scale supermassive black hole dynamics in GADGET-4We present the new public version of the KETJU supermassive black hole (SMBH) dynamics module, as implemented into GADGET-4. KETJU adds a small region around each SMBH where the dynamics of the SMBHs and stellar particles are integrated using an algorithmically regularised integrator instead of the leapfrog integrator with gravitational softening used by GADGET-4. This enables modelling SMBHs as point particles even during close interactions with stellar particles or other SMBHs, effectively removing the spatial resolution limitation caused by gravitational softening. KETJU also includes post-Newtonian corrections, which allows following the dynamics of SMBH binaries below sub-parsec scales down to tens of Schwarzschild radii.
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12:1512:27Chi-HoChanRadiative magnetohydrodynamics simulations of supermassive black hole binaries: Implications for the electromagnetic signatures of LISA verification binariesSupermassive black hole binaries in gas-rich environments may put out distinctive electromagnetic signatures. Binaries with orbital periods of days and merger times of about a decade are of special interest, because they are more abundant than imminent mergers, their luminous output may be modulated on easily detectable timescales, and binaries discovered today will coalesce while LISA is operational. To produce self-consistent electromagnetic predictions for these binaries, we simulate for the first time in Newtonian radiative magnetohydrodynamics the circumbinary disk and minidisks of an equal-mass circular binary. Uniquely, these simulations use realistic opacity and the most accurate radiative transfer prescriptions. With the inclusion of radiative effects, the disks are thinner, denser, and more filamentary, but are otherwise unchanged. Radiation may influence the structure of the lump and the accretion streams. We discuss the observational implications of our simulations.
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18:0018:10GolamShaifullahEvidence for the GWB - On the cusp of Nanohertz GW astronomyI will present the recent results on the evidence for a nanohertz gravitational wave background as detected by pulsar timing arrays. I will discuss the astrophysical interpretations of such a background and the future of low-frequency gravitational wave astronomy.
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18:1018:20LukeKelleyConnecting PTAs with LISA: expectations for MBH mergers based on low-frequency GW measurementsPulsar Timing Arrays (PTAs) have detected strong evidence of spatial correlations indicating a gravitational wave (GW) background in the nanohertz regime. In the NANOGrav PTA’s astrophysics working group, we have developed a new population synthesis framework for modeling massive black hole (MBH) binaries, which we have applied to NANOGrav’s recent 15yr measurements. In this talk, I will present our simulations and update parametric constraints for MBH binary evolution. Using these updated constraints we make predictions for LISA detections of MBHs. I will also discuss prospects for electromagnetic counterparts and host galaxy identification.
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18:2018:30MariaCharisiMulti-messenger observations of supermassive black hole binaries before LISASupermassive black hole binaries produce bright electromagnetic emission and can be detected as quasars with periodic variability. They are also strong sources of low-frequency gravitational waves making them excellent targets for multi-messenger observations. Pulsar Timing Arrays (PTA) will pave the way for multi-messenger detections before LISA launches. I will discuss the benefits of combining gravitational data from PTAs with electromagnetic data from time-domain surveys and the prospects for near-future discoveries
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Friday 15/09
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9:309:42AlejandroTorres OrjuelaDetection of astrophysical gravitational wave sources with TianQin and LISATianQin and LISA are space-based laser interferometer gravitational wave (GW) detectors planned to be launched in the mid-2030s. Both detectors will detect low-frequency GWs around $10^{-2}\,{\rm Hz}$, however, TianQin is more sensitive to frequencies above this common sweet-spot while LISA is more sensitive to frequencies below $10^{-2}\,{\rm Hz}$. Therefore, TianQin and LISA will be able to detect the same sources but with different accuracy for different sources and their parameters. We study the horizon distance and the detection accuracy with which TianQin and LISA will be able to detect some of the most important astrophysical sources -- massive black hole binaries, stellar-mass black holes binaries, double white dwarfs, extreme mass-ratio inspirals, light and heavy intermediate mass-ratio inspirals, as well as the stochastic gravitational background produced by binaries. We, further, study the horizon distance and detection accuracy from joint detections. In particular, we consider the different orientations, lifetimes, and duty cycles of the two detectors to explore how they can give a more complete picture when working together.
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9:429:54AaronStemoIdentifying Weak Links in the LISA MMA Chain from the EM SideThe first multimessenger observations of astronomical objects, combining simultaneous electromagnetic (EM) and gravitational wave (GW) signals, are less than a decade old; but the insights gleaned from them have already begun to address key questions regarding the physics of the universe. The Laser Interferometer Space Antenna (LISA) is set to launch in the 2030’s, at which time it will enable the first observational studies of massive black hole mergers (105 < M < 107 solar mass) – a mass regime not able to be probed by pulsar timing arrays nor ground-based GW observatories. Further, LISA will be able to detect these mergers as soon as a month before coalescence, enabling EM searches to identify and observe the merger system as it evolves in real time. This presents an exciting, but also challenging opportunity to EM observers in many ways. In this talk, I will briefly discuss methodologies that astronomers are considering to rapidly identify the most likely EM counterparts of LISA GW sources in the pursuit of effective multimessenger searches. I will primarily focus on the necessity and difficulty of using large volume, photometric surveys to find EM counterparts – diving into some of the specific challenges (e.g., galaxy and black hole mass estimation) that need to be overcome in order to ensure and maximize LISA’s multimessenger success.
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9:5410:06FilippoMannucciDiscovering the progenitors dual SMBHs at kpc separationsThe calculations of the expected low-frequency GW background and event rate start from the parent population of dual SMBHs at kpc separations produced by the merger of host galaxies. Knowing the main properties of this population (number density, mass distribution, separation distribution, etc.) would provide information on the stage of dynamical friction and reduce the uncertainties of the results on GW. We present an ongoing observational prpgram that allows us to detect, for the first time, a substantial number of dual AGNs in the same host galaxy. We have used Gaia to select many dual AGN candidates at z > 0.5 and separations between ~0.2” and ~0.7”, and obtained resolved spectroscopy of a number of them to classify the systems and study their properties. We have already collected ~15 spectroscopically confirmed dual AGNs with separations below 7kpc and are beginning to investigate their properties.
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10:0610:18ViolaDe RenzisParameter estimation of binary black holes in the endpoint of the up-down instabilityBlack-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti-) aligned spins. Among these, binaries in the up–down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. The occurrence of the up–down instability leads to gravitational-wave sources that formed with aligned spins but are detected with precessing spins. We present a Bayesian procedure based on the Savage-Dickey density ratio to test the up–down origin of gravitational-wave events. This is applied to both simulated signals, which indicate that achieving strong evidence is within the reach of current experiments, and the LIGO/Virgo events released to date, which indicate that current data are not informative enough.
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10:1810:30LudovicaVariscoAn effective model for the tidal disruption of satellites in minor mergersWe are in a unique era for investigating the cosmic growth of galaxies and the black holes they enshroud. Gravitational wave facilities, promise to unveil the hierarchical aggregation of cosmic structures, while Gaia is delivering unprecedented information on the formation history of our Milky Way. Yet, resolution limitations and computational costs of cosmological simulations on one side, and difficulties of simplistic semi-analytical models in accounting for stochastic evolution on the other, make the theoretical modelling of the aggregation of galaxies still very challenging. My project is part of a collective work aiming at building a novel semi-analytical approach able to follow the orbital evolution of massive perturbers (as galaxies and massive black holes) brought into a multi-component, larger galaxy through a minor merger. The model includes a treatment for dynamical friction adapted to flattened and rotating hosts, and accounts for structures as galactic bars, spirals, and massive clumps. I developed a careful prescription for the tidal stripping of extended intruding galaxies; differently from previous works, this prescription is suitable for any geometry of the analytical potential of the primary galaxy. We proved our analytical model to well reproduce the results of N-body simulations for both spherical and flattened hosts. Future prospects of this work include the implementation of a prescription for the cosmological growth of the primary galaxy during the inspiral of the secondary.
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10:3010:42DanielD'OrazioBinary-Disk InteractionsI will discuss recent results on the interaction of a binary with a gaseous medium and its implications for orbital evolution and observability.
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11:1511:27GermanoNardiniConstraining the SOBBH population via SGWB measurements at LISAOne of the LISA mission objective is the detection and characterization of the SGWB. In this talk we illustrate the information on the stellar-mass binary black hole (SmBBH) population that can be inferred thanks to this mission objective. Such information is complementary to the one that LISA will achieve by means of the individual SmBBH event detections, as the SGWB measurement is also sensitive to the population's statistical properties at high-redshift. For the same reason, the SGWB reconstruction may help identify the SmBBH formation channels. We illustrate it in some proof-of-principle cases including PBHs. The science case showed in this talk serves as an illustrative example to highlight some of the AstroWG research lines relevant for the SGWB subWork Package (part of the Science Investigations Work Package).
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11:2711:39Chi AnDong PáezMultimessenger study of merging massive black holes in the Obelisk simulation: gravitational waves, electromagnetic counterparts, and their link to galaxy and black hole populationsMassive black hole (BH) mergers are predicted to be powerful sources of low-frequency gravitational waves (GWs). Coupling the detection of GWs with an electromagnetic (EM) detection can provide key information about merging BHs and their environments. Another important question is how the astrophysical information extracted from BH mergers can inform us about BH evolution. We analyse the high-resolution cosmological radiation-hydrodynamics simulation Obelisk, run to redshift z=3.5, to study the properties of the merging BH population, its differences with the underlying global BH population in terms of BH and galaxy properties, and its detectability in GW and EM domains, modelling spectral energy distribution and obscuration.
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11:3911:51RiccardoBuscicchioFrom mHz to kHz: stochastic background implications on astrophysical sources and population reconstructionStochastic gravitational wave backgrounds (SGWBs) are, to date, yet to be unequivocally observed. At the $nHz$ frequencies, significative evidence for the observation of such signals has been recently reported. In this talk, I will focus on prospects for the detection of SGWBs of astrophysical origin in the $10^{-4} Hz - 10^3 Hz$ frequency range. I will show how recent progress in statistics and data-analysis tools for ground-based detectors might offer the opportunity for an imminent detection of popcorn-like SGWBs. Moreover, I will describe the most recent findings on expected SGWBs of astrophysical origin, observable with future space-based observatories (e.g. LISA). They will pollute the observed datastreams, with far-reaching implications on the parameter reconstruction of individual resolvable sources.
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11:5112:03DavideGerosaA lonely gravitational waveGravitational-wave observations have revealed (LIGO/Virgo) and will be revealing (LISA!) sources whose unusual properties challenge our understanding of compact-binary formation. Inferring the formation processes that are best able to reproduce such events may therefore yield key astrophysical insights. To this end, the current to-go strategy is fitting a catalog of observed events to catalogs of simulated sources. But what if we only get *one* gravitational event? For LIGO, this could be the case for an outlier source that is far from others in parameter space, say GW190521. But for LISA this problem is far more interesting! We will observe a variety of sources, some with limited event rates (multi-band binaries, EMRIs), some spanning an extremely wide parameter space (massive BHs with masses across several orders of magnitude). So, how do you compare a lonely gravitational wave against a population of predicted sources? We present a statically consistent, fully Bayesian solution to this problem. In short, this boils down to computing the posterior odds between two simulated populations while conditioning on selection effects.
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12:0312:15RosaValianteLight and sound from early black holesThe formation of supermassive black holes (SMBHs) of >10^9 Msun at z>6 (e.g., Yang et al. 2020; Wang et al. 2021), less than 1 Gyr after the Big Bang, is still difficult to explain. In order to understand their evolution, it is crucial to investigate the nature of their progenitors, the black hole (BH) seeds, and how they efficiently grow through accretion and mergers across cosmic time. To this aim we are working on developing a new generation of theoretical models for quasar/galaxy formation and evolution with improved descriptions of the main physical processes regulating the formation, growth and feedback of stars and BHs across cosmic epochs. By means of a semi-analytical approach we describe the birth of galaxies and BHs performing a statistical study of the nature and properties of the earliest BH populations, investigating the relative role of different seed formation mechanisms and of gas accretion regimes on the growth of z>6 SMBHs and, at the same time, the imprints of these processes on the mass and luminosity function, at cosmic dawn, especially in the low-end tails of the distributions that is still poorly observationally constrained. I will present the main results of our models, focusing on their connection to the current and future observational campaigns.
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12:1512:27NianyiChenMassive Black Hole Dynamics in and beyond Cosmological Simulations: Bridging the Gap between Galaxy Mergers and Gravitational Wave EmissionAccurate modeling of the massive black hole (MBH) dynamics during and after galaxy mergers is crucial for both correctly predicting the gravitational wave (GW) signals produced by MBH mergers and studying the AGN triggering during galaxy mergers through close-separation dual AGN. In this talk, I will present the recent predictions of MBH merger events from the large-volume, high-resolution cosmological hydrodynamic simulation ASTRID. These predictions incorporate the most up-to-date implementation of sub-grid dynamical friction (DF) from both gas and collisionless matter. By comparing them with a simplified MBH dynamics model, I will demonstrate the necessity of including DF for a better understanding of the detectable MBH merger population by future GW detectors, as well as the kpc-scale dual AGN population. Despite the huge gain from the subgrid DF, modeling the dynamics at sub-kpc scale and of MBH seeds remains a challenging task due to the limit in mass and spatial resolution of cosmological simulations. In the second part of the talk, I will discuss our ongoing efforts to enhance MBH dynamics modeling in large-volume simulations through the resimulation of MBH merger events drawn from the cosmological volume at a higher resolution. Our objective is to bridge the current gap in the dynamical range between kpc-scale, DF-driven orbital decay and parsec-scale loss-cone-driven binary hardening. By doing so, we aim to improve the evaluation of MBH merging timescales and orbital eccentricity evolutions.
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