Signs of `Everything Everywhere All At Once' formation in low surface brightness globular cluster-rich dwarf galaxies

Abstract

Only two ultra-diffuse galaxies (UDGs) have spatially resolved stellar population properties, both showing radially flat-to-rising metallicity profiles, indicative of a different formation pathway to most dwarf galaxies. The scarcity of other low surface brightness (LSB) dwarfs with a similar analysis prevents a deeper understanding on this behaviour. We investigate the radial profiles of the ages, metallicities and star formation histories of four globular cluster (GC) rich LSB dwarfs, newly observed within the 'Analysis of Galaxies At The Extremes' (AGATE) collaboration. DFX1 and DF07 are bona-fide UDGs, while PUDG-R27 and VCC1448 are nearly UDGs (NUDGes). Comparing their and DF44's results to simulations, we aim to reveal their formation pathways. We use pPXF to fit different spectra extracted in annular apertures to recover the stellar population properties and compute their gradients. We compare those with a sample of literature classical dwarfs and simulations, in particular with simulated UDGs. Our five LSB dwarfs present flat age and flat-to-rising metallicity profiles. The flat age gradients are compatible with those of classical dwarfs (both observed and from cosmological simulations), but the metallicity gradient diverges. All of our LSB dwarfs (except for PUDG-R27, showing a pronounced increasing metallicity profile) are compatible with being the extreme tail of the age-metallicity gradient relation, with a preference to co-eval formation forming the galaxy all at once. This sample of GC-rich LSB dwarfs with spatially resolved properties confirms that they seem to follow a different formation path than classical dwarfs. However, larger samples with higher S/N spectra and varying amounts of GC richness are required to set robust constraints on the formation pathways of LSB dwarf galaxies.