Constraining Galactic Structure with the LISA White Dwarf Foreground

TL;DR

This paper demonstrates that analyzing the angular power spectrum of the white dwarf gravitational-wave foreground detected by LISA can effectively measure the vertical scale height of the Milky Way's oldest stellar populations, offering a new method to study Galactic structure.

Contribution

It introduces a novel approach using gravitational-wave foreground anisotropy to constrain the Galactic vertical scale height of white dwarf populations.

Findings

LISA can measure the vertical scale height with 50-200 pc accuracy.

The anisotropy level depends strongly on the population's vertical distribution.

The method provides a new way to probe Galactic structure using gravitational-wave data.

Abstract

White dwarfs comprise 95% of all stellar remnants, and are thus an excellent tracer of old stellar populations in the Milky Way. Current and planned telescopes are not able to directly probe the white dwarf population in its entirety due to its inherently low luminosity. However, the Galactic population of double white dwarf binaries gives rise to a millihertz gravitational-wave foreground detectable by the Laser Interferometer Space Antenna (LISA). Here we show how characterizing this foreground's angular power spectrum will enable us to probe the Galactic structure in a novel way and measure the vertical scale height of the Galaxy's oldest stellar populations. We do this using a binary population synthesis study that incorporates different Galactic spatial distributions for the double white dwarf population. We find that the level of anisotropy in the white dwarf foreground's angular power spectrum is strongly dependent on the vertical scale height of the population. Finally, we show that LISA can probe the vertical scale height of the Galactic double white dwarf population with an accuracy of 50 pc-200pc, depending on angular resolution limits, using the angular power spectrum of the white dwarf foreground.