The star formation history and metallicity in the galactic inner bulge revealed by the RGBB

Observations of the innermost kiloparsec of the Milky Way's bulge are affected by extreme interstellar extinction and source crowding which have posed serious obstacles to the study of its stellar population up to now. Using the 0.2'' angular resolution JHKs data from the new GALACTICNUCLEUS survey, we overcome these challenges and study the stellar population within two fields, about 0.6º and 0.4º to the Galactic north of the Milky Way's centre. We find that the stellar population is old, similar to the one at larger distances from the Galactic plane, and that its metallicity is twice solar, which is consistent with a flat metallicity gradient within about 500 pc of the Galactic centre.