Description
In $\sim 2034$ the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) from $10^5$ to $10^7 \rm M_{\odot}$ up to $z\sim10$. The gravitational wave (GWs) signal is expected to be accompanied by an electromagnetic (EM) counterpart, from radio to X-ray, generated by the gas accreting on the binary.
In this talk, I present some recent results on the standard sirens rates detectable jointly by LISA and EM telescopes. We combine state-of-the-art models for the galaxy formation and evolution with Bayesian tools to perform the parameter estimation of the GW event and estimate the cosmological parameters.
We explore three different astrophysical scenarios employing different seed formation (light or heavy seeds) and delay-time models, in order to have realistic predictions on the expected number of events. We estimate the detectability of the sources in terms of its signal-to-noise ratio in LISA and perform parameter estimation, focusing especially on the sky localization of the source. Exploiting the additional information from the astrophysical models, such as the amount of accreted gas and BH spins, we model the expected EM counterpart to the GW signal in soft X-ray, optical and radio.
Overall, we predict $\sim 14$ standard sirens (stsi) with detectable counterparts over 4 yr of LISA time mission and $\sim 6$ ($\sim 20$) in the pessimistic (optimistic) scenario.
We also explore the impact of absorption from the surrounding gas both for optical and X-ray emission: assuming typical hydrogen and metal column density distribution, we estimate only $\sim 3$ stsi in 4 yr.
Finally we combined the redshift and luminosity distance information to estimate cosmological parameters: we find that $H_0$ can be constrained to few percent precision thanks to few sources whose redshift is measured spectroscopically.
