Clustering Between High-Mass X-Ray Binaries and Ob Associations in the Milky Way

We present the first direct measurement of the spatial cross-correlation function of high-mass X-ray binaries (HMXBs) and active OB star-forming complexes in the Milky Way. This result relied on a sample containing 79 hard X-ray-selected HMXBs and 458 OB associations. Clustering between the two populations is detected with a significance above 7σ for distances <1 kpc. Thus, HMXBs closely trace the underlying distribution of the massive star-forming regions that are expected to produce the progenitor stars of HMXBs. The average offset of 0.4 ± 0.2 kpc between HMXBs and OB associations is consistent with being due to natal kicks at velocities of the order of 100 ± 50 km s−1. The characteristic scale of the correlation function suggests an average kinematical age (since the supernova phase) of ∼4 Myr for the HMXB population. Despite being derived from a global view of our Galaxy, these signatures of HMXB evolution are consistent with theoretical expectations as well as observations of individual objects.