Clustering between high-mass X-ray binaries and OB associations in the Milky Way

TL;DR

This study measures the spatial cross-correlation between high-mass X-ray binaries and OB associations in the Milky Way, revealing their close association and providing insights into their evolution and natal kicks.

Contribution

First direct measurement of the spatial cross-correlation function between HMXBs and OB associations in the Milky Way, linking their distribution and evolutionary history.

Findings

HMXBs are significantly clustered with OB associations within 1 kpc.

Average offset of 0.4 kpc suggests natal kicks at ~100 km/s.

Correlation scale indicates an average age of ~4 Myr for HMXBs.

Abstract

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 7-sigmas 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. 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.