Looking into the FaintEst WIth MUSE
(LEWIS)
With LEWIS we will obtain the first homogeneous integral-field spectroscopic survey of UDGs in a cluster environment with MUSE.
The target is the Hydra I cluster, at ~50Mpc, where a complete sample of UDG candidates, made by 32 objects in total, have been recently discovered inside 0.6 virial radius of the cluster (Iodice et al. 2020; La Marca, Iodice et al. 2021).
With the MUSE data we will confirm their cluster membership, measure their stellar kinematics and stellar populations.
The stellar population properties (ages and metallicity) together with the baryonic versus DM fraction will be used in comparison with hydrodynamical models of UDGs to establish their formation channels as a function of their location in the cluster.
The MUSE data will also establish the GC population and their specific frequency within 1.5Re for each UDG. This will provide an independent handle on the DM content in these systems.
To date, due to their LSB nature, similar studies are available only for about 20 UDGs in total, mainly in the Coma cluster, and only few UDGs have integral-field spectroscopy. By doubling the number of spectroscopically studied UDGs and obtaining a homogeneous survey of these extreme LSB galaxies in the Hydra I cluster, the LEWIS project aims at addressing the open actively debated issues on the UDG nature and formation in a cluster environment.