Constraining the Black Hole Initial Mass Function with LIGO/VIRGO Observations

Rosalba Perna; Yi-Han Wang; Will M. Farr; Nathan Leigh; Matteo Cantiello

doi:10.3847/2041-8213/ab2336

paper

Constraining the Black Hole Initial Mass Function with LIGO/VIRGO Observations

arXiv:1901.03345 · doi:10.3847/2041-8213/ab2336

Abstract

Prior to the detection of black holes (BHs) via the gravitational waves (GWs) they generate at merger, the presence of BHs was inferred in X-ray binaries, mostly via dynamical measurements, with masses in the range between $\sim 5 - 20 M_{⊙}$ . The LIGO discovery of the first BHs via GWs was surprising in that the two BHs that merged had masses of $35. 6_{- 3.0}^{+ 4.8}$ and $30. 6_{- 4.4}^{+ 3.0} M_{⊙}$ , which are both above the range inferred from X-ray binaries. With 20 BH detections from the O1/O2 runs, the distribution of masses remains generally higher than the X-ray inferred one, while the effective spins are generally lower, suggesting that, at least in part, the GW-detected population might be of dynamical origin rather than produced by the common evolution of field binaries. Here we perform high-resolution N-body simulations of a cluster of isolated BHs with a range of initial mass spectra and upper mass cut-offs, and study the resulting binary mass spectrum resulting from the dynamical interactions. Our clusters have properties similar to those of the massive remnants in an OB association $\sim 10 Myr$ after formation. We perform a likelihood analysis for each of our dynamically-formed binary population against the data from the O1 and O2 LIGO/Virgo runs. We find that an initial mass spectrum $M_{BH} \propto M^{- 2.35}$ with an upper mass cutoff $M_{max} \sim 50 M_{⊙}$ is favored by the data, together with a slight preference for a merger rate that increases with redshift.

Accepted to ApJL. Major updates

Constraining the Black Hole Initial Mass Function with LIGO/VIRGO Observations

Abstract

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