Understanding stellar populations in thin and thick discs of edge-on galaxies with MUSE – I. The case of the reignited S0 galaxy ESO 544-27

ABSTRACT Edge-on galaxies act as the best laboratories to understand the origin of thin and thick discs in galaxies. Measurement of spatially resolved stellar population properties in such galaxies, particularly age, metallicity, and α/Fe, are crucial to understanding the formation and evolution of disc galaxies. Such measurements are made possible from stellar population model fits to deep integral field spectroscopic (IFU) observations of resolved galaxies. We utilize archival MUSE IFU observations of the edge-on galaxy ESO 544-27 to uncover the formation history of its thin and thick discs through its stellar populations. We find the thin disc of the galaxy is dominated by an old (9 Gyr) low α/Fe metal-rich stellar population. Its outer thick disc is dominated by an old (9 Gyr) high α/Fe metal-rich component that should have formed with higher star formation efficiency than the Milky Way thick disc. We thus find α/Fe dichotomy in ESO 544-27 with its thin and thick discs dominated by low and high α/Fe stellar populations, respectively. However, we also find a metal-rich younger (2 Gyr old) stellar population in ESO 544-27. The galaxy was nearly quenched until its star formation was reignited recently first in the outer and inner thick disc (∼1 Gyr ago) and then in the thin disc (∼600 Myr ago). We thus find that both the low α/Fe thin and high α/Fe thick discs of ESO 544-27 are inhabited primarily by similarly old metal-rich stellar populations, a contrast to that of other galaxies with known thin and thick disc stellar population properties.