The Galactic distribution of X-ray binaries and its implications for compact object formation and natal kicks

TL;DR

This study investigates how different models of black hole and neutron star formation influence the distribution of X-ray binaries in the Galaxy, using their vertical height as a key indicator to distinguish formation scenarios and natal kicks.

Contribution

It demonstrates that the vertical distribution of X-ray binaries effectively constrains black hole and neutron star formation models and natal kick velocities.

Findings

High natal kicks are consistent with observed black hole X-ray binaries.

Neutron star X-ray binaries favor high natal kick distributions aligned with pulsar data.

Binary evolution after formation has minimal impact on Galactic distribution patterns.

Abstract

The aim of this work is to study the imprints that different models for black hole (BH) and neutron star (NS) formation have on the Galactic distribution of X-ray binaries (XRBs) which contain these objects. We find that the root mean square of the height above the Galactic plane of BH- and NS-XRBs is a powerful proxy to discriminate among different formation scenarios, and that binary evolution following the BH/NS formation does not significantly affect the Galactic distributions of the binaries. We find that a population model in which at least some BHs receive a (relatively) high natal kick fits the observed BH-XRBs best. For the NS case, we find that a high NK distribution, consistent with the one derived from the measurement of pulsar proper motion, is the most preferable. We also analyse the simple method we previously used to estimate the minimal peculiar velocity of an individual BH-XRB at birth. We find that this method may be less reliable in the bulge of the Galaxy for certain models of the Galactic potential, but that our estimate is excellent for most of the BH-XRBs.