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

TL;DR

This study investigates how the distribution of Mira variable stars in the Milky Way's central region varies with age, revealing an age-morphology dependence of the galaxy's boxy/peanut bulge through observational data and simulation comparison.

Contribution

It demonstrates the age-dependent spatial distribution of Mira variables and links it to the morphology of the Milky Way's bulge using simulation models.

Findings

Older Miras are more symmetrically distributed around the Galactic center.

Younger Miras show a shift towards negative Galactic longitudes.

The observed distribution is influenced by projection effects and observational limitations.

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.