Gaia DR3 data consistent with a short bar connected to a spiral arm

We use numerical simulations to model Gaia DR3 data with the aim of constraining the Milky Way (MW) bar and spiral structure parameters. We show that both the morphology and the velocity field in MW-like galactic disc models are strong functions of time, changing dramatically over a few tens of Myr. This suggests that by finding a good match to the observed radial velocity field, v(R)(x, y ), we can constrain the bar -spiral orientation. Incorporating uncertainties into our models is necessary to match the data; most importantly, a heliocentric distance uncertainty abo v e 10-15 per cent distorts the bar's shape and v(R) quadrupole pattern morphology, and decreases its apparent angle with respect to the Sun-Galactocentric line. An excellent match to the Gaia DR3 v(R)(x, y ) field is found for a simulation with a bar length R-b approximate to 3.6 kpc. We argue that the data are consistent with an MW bar as short as similar to 3 kpc, for moderate strength inner disc spiral structure ( A(2)/A(0) approximate to 0.25) or, alternatively, with a bar length up to similar to 5.2 kpc, provided that spiral arms are quite weak ( A(2)/A(0) approximate to 0.1), and is most likely in the process of disconnecting from a spiral arm. We demonstrate that the bar angle and distance uncertainty can similarly affect the match between our models and the data - a smaller bar angle (20 degrees instead of 30 degrees) requires smaller distance uncertainty (20(degrees) instead of 30(degrees)) to explain the observations. Fourier components of the face -on density distribution of our models suggest that the MW does not have strong m = 1 and/or m = 3 spirals near the solar radius.