Abstract
ABSTRACT The Laser Interferometer Space Antenna (LISA) will enable Galactic gravitational wave (GW) astronomy by individually resolving >104 signals from double white dwarf (DWD) binaries throughout the Milky Way. Since GWs are unaffected by stellar crowding and dust extinction unlike optical observations of the Galactic plane, in this work, we assess for the first time the potential of LISA to map the Galactic stellar bar and spiral arms. To achieve this goal, we combine a realistic population of Galactic DWDs with a high-resolution N-body Galactic simulation in good agreement with current observations of the Milky Way. We then model GW signals from our synthetic DWD population and reconstruct the structure of the simulated Galaxy from mock LISA observations. Our results show that while the low-density contrast between the background disc and the spiral arms hampers our ability to characterize the spiral structure, the stellar bar will clearly appear in the GW map of the bulge. The axial ratio derived from the synthetic observations agrees within 1σ with the reference value, although the scale lengths are underestimated. We also recover the bar viewing angle to within 1° and the bar’s physical length to within 0.2 kpc. This shows that LISA can provide independent constraints on the bar’s structural parameter, competitive compared to those from electromagnetic tracers. We therefore foresee that synergistic use of GWs and electromagnetic tracers will be a powerful strategy to map the Milky Way’s bar and bulge.
Highlights
It is established that the Milky Way has a central stellar bar and a spiral structure that propagates through its stellar and gaseous disc
We repeat the procedure for 104 realisations of the binary positions in the Galaxy
Each realisation is obtained by randomly drawing distances and sky positions from Gaussian distributions centred on the measured values, with standard deviation equal to the measurement errors provided by the Mock LISA Data Challenge (MLDC) pipeline
Summary
It is established that the Milky Way has a central stellar bar and a spiral structure that propagates through its stellar and gaseous disc. The amplitude, length and pattern speed of the stellar bar are debated, and constant effort to determine their values is motivated by their importance for a broad range of Galactic studies. These bar features are key to understanding the properties of the disc outside the stellar bar (Minchev & Famaey 2010), the kinematics in the solar neighbourhood Aguerri 2020; Monari et al 2019), and the observed non-circular gas flow (e.g., Bissantz et al 2003)
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