Periodic Reporting for period 1 - MASSIVEBAYES (Bayesian inference of massive black hole binaries formation and evolution scenarios with gravitational waves)
Reporting period: 2022-12-01 to 2024-11-30
The scope of my project is to use gravitational wave (GW) observations to answer open questions in astrophysics and cosmology. To achieve this, I propose to use the GW signals generated by the coalescence of massive black hole binaries (MBHBs) detected by the forthcoming Laser Interferometer Space Antenna (LISA).
In the standard cosmological scenario, dark matter halos merge leading to the structure formation along the filaments of the cosmic web. These regions are the birthplace of the first seed black holes (BHs) and proto-galaxies that grow together through episodes of accretion and merger leading to the massive BHs (MBHs) that we currently observe in the center of galaxies. MBHs are expected to interact with their host galaxies, leading to a complex evolutionary path where each actor influences the other. For example, MBHs can grow throughout accretion phases while the in-falling gas powers strong jets and disk winds that act as a feedback mechanism on the host galaxy.
If the galaxies are brought sufficiently close, the MBHs residing at their centers might bind and form a binary that will eventually coalesce emitting GWs. In ~2034 LISA, the third Large class mission of the European Space Agency (ESA), will be able to observe GWs from the coalescence of MBHBs in the milli-hertz domain throughout the entire Universe.
MBHBs are one of the core targets of LISA mission: coalescing at a typical frequency of milli-hertz, these sources are not accessible to ground-based (present and future) GW detectors operating in the frequency band above few Hz, and, even if there are binary AGN candidates, LISA will be the only instrument to observe MBHBs at sub-parsec scale. The promised LISA scientific case for MBHBs is outstanding: scanning the entire Universe with GWs, LISA will be able not only to provide exquisite estimate of the binary parameters such as masses and luminosity distance but especially to shed light on the history merger of MBHBs and on the astrophysical processes driving their evolution. Thanks to the close interplay between MBH and the host galaxy, GWs from MBHBs are an excellence way to investigate their formation and evolution. Moreover, if an electromagnetic (EM) counterpart is emitted together with the GW signal, multimessenger observations of MBHBs are the perfect tools to test the expansion of the Universe and to perform tests of General Relativity.
In the standard cosmological scenario, dark matter halos merge leading to the structure formation along the filaments of the cosmic web. These regions are the birthplace of the first seed black holes (BHs) and proto-galaxies that grow together through episodes of accretion and merger leading to the massive BHs (MBHs) that we currently observe in the center of galaxies. MBHs are expected to interact with their host galaxies, leading to a complex evolutionary path where each actor influences the other. For example, MBHs can grow throughout accretion phases while the in-falling gas powers strong jets and disk winds that act as a feedback mechanism on the host galaxy.
If the galaxies are brought sufficiently close, the MBHs residing at their centers might bind and form a binary that will eventually coalesce emitting GWs. In ~2034 LISA, the third Large class mission of the European Space Agency (ESA), will be able to observe GWs from the coalescence of MBHBs in the milli-hertz domain throughout the entire Universe.
MBHBs are one of the core targets of LISA mission: coalescing at a typical frequency of milli-hertz, these sources are not accessible to ground-based (present and future) GW detectors operating in the frequency band above few Hz, and, even if there are binary AGN candidates, LISA will be the only instrument to observe MBHBs at sub-parsec scale. The promised LISA scientific case for MBHBs is outstanding: scanning the entire Universe with GWs, LISA will be able not only to provide exquisite estimate of the binary parameters such as masses and luminosity distance but especially to shed light on the history merger of MBHBs and on the astrophysical processes driving their evolution. Thanks to the close interplay between MBH and the host galaxy, GWs from MBHBs are an excellence way to investigate their formation and evolution. Moreover, if an electromagnetic (EM) counterpart is emitted together with the GW signal, multimessenger observations of MBHBs are the perfect tools to test the expansion of the Universe and to perform tests of General Relativity.
In the first year, I explored the possible multimessenger synergies between LISA and future EM facilities. I analysed a population of MBHBs and, for each event, I simulated the GW signal, evaluating LISA ability to reconstruct the sky position of the event, a key information for the search of EM counterparts. Together with the GW signal, I also modeled the EM counterparts in radio, optical and X-ray band to get an independent estimate of the redshift. I found that we expect between 7 and 20 multimessenger MBHB events with LISA in 4 years of observations. However these numbers decrease to just 2-3 events in 4 years in some models where absorption and collimated radio emission are included. The end-product of the study was a catalogue of events that could be used for cosmological inference.
With the population of MBHBs with detectable EM counterparts, I started exploring the constraints we can put on the expansion of the Universe. I develop a code for the cosmological inference and tested several cosmological models as well as model-independent approach. I found that MBHBs can constrain the Hubble factor down to ~10% at redshift z=2-3, a poorly explore range in cosmology due to the lack of observations. My results correspond to the state-of-the-art predictions of the capabilities of LISA and further support its science objectives.
With the population of MBHBs with detectable EM counterparts, I started exploring the constraints we can put on the expansion of the Universe. I develop a code for the cosmological inference and tested several cosmological models as well as model-independent approach. I found that MBHBs can constrain the Hubble factor down to ~10% at redshift z=2-3, a poorly explore range in cosmology due to the lack of observations. My results correspond to the state-of-the-art predictions of the capabilities of LISA and further support its science objectives.
I found that MBHBs represent excellent tools to perform cosmological tests: while the previous studies focused mostly on local measurements, i.e. trying to constrain the Hubble constant or the local matter density, I employed multimessenger MBHB observations to probe the Universe up to redshift z~7. We tested several cosmological models where we managed to reach an accuracy of 20% on the Hubble parameter.
However, the most promising results come from a model-independent approach based on the splines interpolation in which we approximate the relation between luminosity distance and redshift with a set of cubic polynomials. According to this model-independent approach, the constraints on the Hubble parameter at z~2 can be of the order of ~10%. This approach has never been tested and it represents a change in the idea of MBHBs as cosmological probes: even if these sources might not be able to be competitive with other probes as observations from Cosmic Microwave Background or Supernovae, they will still be able to give us additional information at intermediate redshifts.
However, the most promising results come from a model-independent approach based on the splines interpolation in which we approximate the relation between luminosity distance and redshift with a set of cubic polynomials. According to this model-independent approach, the constraints on the Hubble parameter at z~2 can be of the order of ~10%. This approach has never been tested and it represents a change in the idea of MBHBs as cosmological probes: even if these sources might not be able to be competitive with other probes as observations from Cosmic Microwave Background or Supernovae, they will still be able to give us additional information at intermediate redshifts.