We would like to contribute in the definition of cutting-edge science questions for LISA. In particular:

• Do high redshift LISA black holes merge “on clock” when halos merge or is there a time delay between formation of the new halo and black hole merging? What are the physical processes ruling the massive black hole dynamics? How time delays vary with redshift and with properties of the galaxy halos? To what extent do time delays affect the massive black hole merger rate? What is the chirp mass and spin distribution of LISA massive black hole binary coalescences, and what is the rate of coalescence events as function of redshift and mass ratio?

• Do massive black hole mergers have an associated ElectroMagnetic (EM) counterpart, and if so, how fast can we identify the EM signal when the binary sweeps through the LISA band? How fast sky localization will become available to alert ground and space based observatories to search for an EM counterpart? Does the EM signal anticipate the merger proper, and if so what is the best time window for sending alerts? How would the EM signal be modulated by spin precession in the early phases of the inspiral? How do the black hole spins couple with the mini-discs orbiting around the inspiralling black holes to leave clear signatures of an ongoing merger? What is the expected EM light curve and spectrum? Does it extend from radio to gamma-rays or is there a main contribution in the optical from the mini-accretion discs?

• How observations of DUAL AGN, QSOs and active black holes in dwarf galaxies tell us about the merging rates, the extent of recoils and the ubiquity of black holes in galaxies below redshift of a few?

• Is the LISA horizon for stellar origin black hole deep enough to detect the mass gap in the stellar black hole population, as predicted in stellar evolution models? Can we envisage multi-band observations of heavy stellar black holes with LIGO-Virgo to help localizing the source year-months-weeks before the merger?

The Group is structured into four Working Groups in order to fulfill the commitment to the LISA Consortium and contribute to advances in the science for LISA:

• Astro-WG-Dynamics

• Astro-WG-Catalog

• Astro-WG-EM counterpart

• Astro-WG-X