The recent detection of gravitational waves has proven the existence of massive stellar black hole binaries (BBHs) and has opened a new window on the Universe.
In this work, we study the cosmic merger rate density of BBHs, intending to put some constraints on their possible formation channel, which remains an open question. Here, we adopt an innovative approach to investigate the cosmic history of BBH mergers. We combine extended population-synthesis simulations, performed with MOBSE, with the Illustris cosmological simulation. In particular, we consider different population-synthesis models, varying the prescription of some key processes like supernova explosions, common-envelope evolution, and natal kicks.
We find that the normalization of the cosmic BBH merger rate strongly depends on the treatment of common envelope and the distribution of natal kicks (see the figure on the bottom). Our analyses also show that most merging BBHs within LIGO’s instrumental horizon come from relatively metal-poor progenitors (Z <= 0.004). In particular, the heavy systems, like GW150914, that merge in the local Universe appear to have formed at high redshift, with a long delay time.
This study represents the first work where MOBSE has been used, but it will be presented in full detail in upcoming posts/articles. Thus, stay tuned.
Left y-axis: Cosmic merger rate density of BBHs (in the plot referred as BHBs) in the comoving frame, as a function of the look-back time (bottom x-axis) and of the redshift (top x-axis) adopting our models (see Table 1 in Mapelli et al. 2017 for more details). Red solid line: D (fiducial model); black dashed line: R; violet dash-dot line: DHG; orange dashed line: DK; blue dotted line: D0.02; green dash-dot line: D1.5. Green-shaded area: BBH merger rate inferred from LIGO detections (Abbott et al. 2016a). Right y-axis: cosmic SFR density from the Illustris (grey thin solid line), as a function of the look-back time (bottom x-axis) and of the redshift (top x-axis).