The spatially resolved star formation history of the dwarf spiral galaxy NGC 5474
Östlin, G.; Cignoni, M.; Tosi, M.; Sabbi, E.; Calzetti, D.; Adamo, A.; Johnson, Kelsey E.; Bellazzini, M.; Dale, Daniel A.; Gallagher, John S.; Linden, Sean T.; Messa, M.; Grasha, K.; Sacchi, E.; Wofford, A.; Fumagalli, M.; Annibali, F.; Pascale, R.; Bortolini, G.
Sweden, Italy, Germany, United States, Australia, Mexico
Abstract
We study the resolved stellar populations and derive the star formation history of NGC 5474, a peculiar star-forming dwarf galaxy at a distance of ~7 Mpc, using Hubble Space Telescope Advanced Camera for Surveys data from the Legacy Extragalactic UV Survey (LEGUS) programme. We apply an improved colour-magnitude diagram fitting technique based on the code SFERA and use the latest PARSEC-COLIBRI stellar models. Our results are the following. The off-centre bulge-like structure, suggested to constitute the bulge of the galaxy, is dominated by star formation (SF) activity initiated 14 Gyr ago and lasted at least up to 1 Gyr ago. Nevertheless, this component shows clear evidence of prolonged SF activity (lasting until ~10 Myr ago). We estimate the total stellar mass of the bulge-like structure to be (5.0 ± 0.3) × 108 M⊙. Such a mass is consistent with published suggestions that this structure is in fact an independent system orbiting around and not within NGC 5474's disc. The stellar overdensity located to the South-West of the bulge-like structure shows a significant SF event older than 1 Gyr, while it is characterized by two recent peaks of SF, around ~10 and ~100 Myr ago. In the last Gyr, the behaviour of the stellar disc is consistent with what is known in the literature as 'gasping'. The synchronized burst at 10-35 Myr in all components might hint to the recent gravitational interaction between the stellar bulge-like structure and the disc of NGC 5474.