Recent progress in gravitational-wave and multi-messenger astronomy poses new questions in a wide range of astrophysical topics, from the evolution of massive stars to super-massive black holes, from multi-wavelength observations of high-energy sources to cosmology and galaxy evolution. Clearly, a coordinated effort from the community is required to take full advantage of this new observational window. Indeed, gravitational- wave astronomy provides the opportunity for new collaborations across different astrophysical fields. We propose to discuss these exciting synergies in a dedicated workshop organized by the « Source populations » and « Multi-messenger Astronomy » Working Groups of the GdR « Ondes Gravitationnelles » and the national programs PNCG, PNPS and PNHE. The goal of this workshop is to present the latest results of the field to the French astrophysics community and to inspire cross-disciplinary discussions, in particular in the context of upcoming missions.

The workshop will be divided into two afternoon sessions. One session, planned in coordination with PNHE and PNPS, will be devoted to stellar-mass sources of gravitational waves, the evolution of their stellar progenitors and the properties of their host galaxies. A particular emphasis will be given to high-energy astrophysics and electromagnetic counterparts to gravitational-wave sources. We will also discuss recent discoveries from the ground-based instruments LIGO and Virgo as well as the future Einstein Telescope.

Another session, planned in coordination with PNCG will target intermediate and super- massive black holes and their role to structure matter at different scales in the Universe, applications to cosmography, such as measurements of the Hubble constant, stochastic backgrounds and cross-correlations with galaxy catalogues. We will focus on the future space mission LISA and its possible synergies with electromagnetic missions, and on the exciting recent progress of Pulsar Timing Array measurements, which open strong connections with extragalactic astrophysics and galaxy evolution.

Co-chair : Irina Dvorkin ; Francesca Calore ; Sylvain Chaty ; Olivier Godet ; Astrid Lamberts ; Gilles Theureau ; Marta Volonteri