Bulges and discs in nearby galaxies have complex structures, resulting from a large diversity of possible assembly histories. In this seminar, I will show how we use deep MUSE observations of nearby edge-on disc galaxies to study the connection between galaxy morphology and assembly history, and to probe the growth of discs with time and constrain disc settling and vertical heating. I will show that discs can settle very early, and can form bars quickly, and I will discuss the complex impact of mergers on disc thickening and bulge growth. I will also show that lenticular galaxies in the Fornax cluster form an interesting comparison point, with weak secular evolution and stunted radial growth because of the lack of fresh gas. Finally, I will give an overview of GECKOS, an ongoing MUSE survey of 36 nearby edge-on Milky Way-mass galaxies.

RR Lyrae stars have long been considered unequivocal tracers of old (>10 Gyr) metal-poor (<-0.5) stellar populations. First, because these populations are where they are most easily found; but also because, according to canonical stellar evolution models for isolated stars, these are the only populations where RR Lyrae should exist. Recent independent results, however, are challenging this view and pointing at the existence of intermediate-age RR Lyrae, only a few (2-5) Gyrs old.

In this seminar I will present the first detection of an RR Lyrae star reliably associated to an intermediate-age cluster: the nearby 2 Gyr-old Trumpler 5. I will frame this result in the context of recent works and of our findings for the expected and observed rates of these stars per unit mass, both from observations of intermediate-age clusters in the Magellanic Clouds, as well as from previous results on possible binary evolution origins for these stars. The association of an RRL star to a decidedly intermediate-age simple stellar population is, so far, the most direct evidence of the existence of these ‘young’ RRLs and adds firm support to the evidence that has been systematically accumulating toward the existence of these highly controverted stars.