The formation and coalescence sites of the first gravitational wave events

Abstract

We present a novel theoretical model to characterize the formation and coalescence sites of compact binaries in a cosmological context. This is based on the coupling between the binary population synthesis code SeBa with a simulation following the formation of a Milky Way-like halo in a well resolved cosmic volume of 4 cMpc, performed with the GAMESH pipeline. We have applied this technique to investigate when and where systems with properties similar to the recently observed LIGO/VIRGO events are more likely to form and where they are more likely to reside when they coalesce. We find that more than 70% of GW151226 and LVT151012-like systems form in galaxies with stellar mass M* > 10^8 Msun in the redshift range [0.06 - 3] and [0.14 - 11.3], respectively. All GW150914-like systems form in low-metallicity dwarfs with M* < 5 10^6 Msun at 2.4 < z < 4.2. Despite these initial differences, by the time they reach coalescence the observed events are most likely hosted by star forming galaxies with M* > 10^{10} Msun. Due to tidal stripping and radiative feedback, a non negligible fraction of GW150914-like candidates end-up in galaxies with properties similar to dwarf spheroidals and ultra-faint satellites.