Age-morphology dependence of the Milky Way boxy/peanut bulge seen in Mira variables

Abstract

We analyse the distribution of Mira variable stars in the central region of the Milky Way. We find that with increasing period, i.e. decreasing age, the Miras shift towards negative Galactic longitudes $\ell$. Comparing to a cosmological zoom simulation of a barred galaxy, we find that this shift with age can be explained by an age-morphology dependence of the boxy peanut/bulge. Owing to a combination of projection effects and the limitation of the range of Galactic longitudes, the near hump at $\ell >0$ is more truncated for younger populations, and the far hump at $\ell <0$ dominates the observed distributions.

5 pages, 4 figures, submitted to MNRAS

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• A three-dimensional map of the Milky Way using 66,000 Mira variable stars
• Hunting for C-rich long-period variable stars in the Milky Way's bar-bulge using unsupervised classification of Gaia BP/RP spectra
• Deciphering the Milky Way disc formation time encrypted in the bar chrono-kinematics