Joint Astrophysical Colloquium
Unveiling the faintest side of the Universe: discoveries, structure and open issues on ultra-diffuse galaxies
Enrichetta Iodice (INAF-OACN)
Thursday 26/03/2026 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
The subject of this talk is an intriguing class of objects: the ultra-diffuse galaxies (UDGs). UDGs are among the faintest and lowest surface-brightness galaxies known in the Universe, having a central luminosity mu_g,0<24 mag/arcsec2, and effective radius (Re) larger than 1.5 kpc. Even considering that low-surface brightness (LSB) galaxies were first recognized in the 80s (Sandage & Binggeli 1984; Impey+1988; Ferguson & Sandage 1988; Bothun+1991), UDGs were introduced as a new class of objects later in 2015, by van Dokkum+2015. They detected several extremely faint and diffuse galaxies in the Coma cluster, with an effective radius similar to that of the Milky Way (Re ~4.5 kpc), but with a ~100 times smaller stellar mass. Being so diffuse and faint, van Dokkum+2015 suggested that, to survive the tidal gravitational interactions in the cluster, UDGs should host a large amount of dark matter (DM). This brought ever-increasing attention to the detection and study of UDGs. Ten years after the first paper introducing UDGs, many efforts have been devoted to deriving the structural properties of this mysterious class of objects. In this talk I would like to i) review the state-of-the art on UDGs’ science, from both observational and theoretical sides, providing how much this field of research improved thanks to the advances in instrument developments, and ii) illustrate the groundbreaking results we are obtaining from two large projects that I am leading: 1) Looking into the faintEst WIth MUSE (LEWIS), focused on structural properties of UDGs from integral-field spectroscopy, and 2) Exploring the extreme universe: a preview of the galaxy Structure to be Unveiled from the Next geneRatIon aStronomical survEys (SUNRISE), focused on the detection and analysis of UDGs from deep imaging surveys.