Populating the Galaxy with pulsars - II. Galactic dynamics

Pulsar observations provide a suite of tests to which stellar and binary evolutionary theory may compare. Importantly, the number of pulsar systems found from recent surveys has increased the statistical significance of pulsar population synthesis results. To take advantage of this, we are in the process of developing a complete pulsar population synthesis code that accounts for isolated and binary pulsar evolution, Galactic spatial evolution and pulsar survey selection effects. In a recent paper, we described the first component of this code and explored how uncertainties in the parameters of binary and pulsar evolution affected the appearance of the pulsar population in terms of magnetic field and spin period. We now describe the second component which focuses on following the orbits of the pulsars within the Galactic potential. In combination with the first component, we produce synthetic populations of pulsars within our Galaxy and calculate the resulting scaleheights as well as the radial and space velocity distributions of the pulsars. Correlations between the binary and kinematic evolution of pulsars are also examined. Results are presented for isolated pulsars, binary pulsars and millisecond pulsars. We also test the robustness of the outcomes to variations in the assumed form of the Galactic potential, the birth distribution of binary positions and the strength of the velocity kick given to neutron stars at birth. We find that isolated pulsars have a greater scaleheight than binary pulsars. This is also true when restricted to millisecond pulsars unless we allow for low-mass stars to be ablated by radiation from their pulsar companion in which case the isolated and binary scaleheights are comparable. Double neutron stars are found to have a large variety of space velocities; in particular, some systems have speeds similar to the Sun. We look in detail at the predicted Galactic population of millisecond pulsars with black hole companions, including their formation pathways, and show where the short-period systems reside in the Galaxy. Some of our population predictions are compared in a limited way to observations but the full potential of this aspect will be realized in the near future when we complete our population synthesis code with the selection effects component.