The Average Age Map of the Galactic Bulge

TL;DR

This study maps the average stellar ages across the Galactic Bulge, revealing a significant age gradient that supports different formation scenarios for the bulge's components.

Contribution

It provides the first detailed age distribution map of the Galactic Bulge using high-precision photometry and red giant star tracers, highlighting a systematic age gradient.

Findings

Mean stellar age increases with galactic latitude.

Younger population near the plane (~4.7 Gyr), older population at higher latitudes (~10.5 Gyr).

Supports dual formation scenarios for the bulge components.

Abstract

The Galactic Bulge, as the center of the Galaxy, is the closest laboratory for studying galaxy formation and evolution. However, its study faces significant challenges due to heavy dust extinction. This paper is devoted to deriving the average age of the Galactic Bulge and investigating its spatial distribution. We utilize a high-precision PSF-fitting photometric catalogue in the $J$ and $K_{\mathrm{s}}$ bands observed by VISTA to study the average stellar ages within the Bulge. Red giant stars are employed as tracers, with their average distances determined using red clump stars as references. The average ages are fitted with stellar models. Our analysis reveals a systematic age gradient across the Galactic Bulge ($2^{\circ} < |b| < 8^{\circ}$). The mean stellar age increases significantly with galactic latitude, shifting from a younger population ($\sim 4.69^{+0.97}_{-0.81}$ Gyr) prevalent near the plane to a predominantly older population ($\sim 10.48^{+0.93}_{-0.85}$ Gyr) at higher latitudes. We hypothesize that the young stellar population at low latitudes is predominantly composed of a pseudo-bulge formed via disk/bar processes (incorporating contributions from recent star-forming activity in the Galactic center), whereas the older stellar population is associated with spheroidal bulges generated through early-stage collapse or accretion of debris from merged dwarf galaxies.