The spatially resolved star formation history of the dwarf spiral galaxy NGC 5474

TL;DR

This study uses Hubble data to map the detailed star formation history of NGC 5474, revealing prolonged activity in its bulge-like structure and recent interactions affecting its stellar populations.

Contribution

It presents an improved colour-magnitude diagram fitting technique and provides the first detailed spatially resolved star formation history of NGC 5474.

Findings

The bulge-like structure formed stars over 14 Gyr, with activity until 10 Myr ago.

The south-west over-density experienced star formation over 1 Gyr ago with recent peaks.

The galaxy's disc shows a 'gasping' star formation pattern in the last Gyr.

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 $\sim 7$ Mpc, using Hubble Space Telescope Advanced Camera for Surveys data from the Legacy Extragalactic UV Survey (LEGUS) program. 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 $\sim 10$ Myr ago). We estimate the total stellar mass of the bulge-like structure to be $(5.0 \pm 0.3) \times 10^{8}$ \MSUN. 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 over-density located to the South-West of the bulge-like structure shows a significant SF event older than $1$ Gyr, while it is characterised by two recent peaks of SF, around $\sim10$ and $\sim100$ Myr ago. In the last Gyr, the behavior of the stellar disc is consistent with what is known in the literature as `gasping'. The synchronised 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.