Mid-Infrared Enhanced Lenticulars caught in the dusty midst of transformation in the Coma Cluster

We explore the properties of early-type galaxies (ETGs) in rich environments such as clusters of galaxies. The L₂₄/L _K distribution of ETGs in both Virgo and Coma clusters shows that some lenticulars (S0, 10 in Coma and 3 in Virgo) have a much larger L₂₄/L _K ratio (0.5 to ~2 dex) than the bulk of the ETG population. We call these sources Mid-Infrared Enhanced Galaxies (MIEGs). In Coma, they are mostly located in the South-West part of the cluster where a substructure is falling onto the main cluster. MIEGs present lower g-r color than the rest of the ETGs, because of a blue continuum. We interpret the excess L₂₄/L _K ratio as evidence for an enhanced star-formation induced as a consequence of their infall into the main cluster.