Chemical signature reveals co-spatial dwarf satellite of an edge-on disc galaxy with MUSE

ABSTRACT Integral field unit (IFU) spectroscopic observations of resolved galaxies provide an optimal experimental setting for determination of stellar population properties, in particular – age, metallicity, and $\alpha$-enhancement, which are key to understanding evolution of galaxies across diverse physical environments. We determine these properties for the edge-on disc galaxy IC 1553, through stellar population models fitted to MUSE IFU observations. From our determined spatial distributions of metallicity and [$\alpha$/Fe], we serendipitously identify the unique chemical signature of a dwarf galaxy that is co-spatial with the luminous disc of IC 1553. The dwarf galaxy is characterized by the presence of higher [$\alpha$/Fe] and metal-poor stellar populations relative to the disc of IC 1553. The identified dwarf is dynamically cold from its determined kinematics, consistent with being a satellite of IC 1553. From modelling the Spitzer IRAC 3.6 $\mu \mathrm{ m}$ image of IC 1553, we confirmed the presence of the dwarf galaxy and calculated its stellar mass to be $\sim 1.28\times 10^{9} \rm ~{\rm M}_{\odot }$. This is the first such identification of a dwarf galaxy from its unique chemical signature in such integrated light IFU observations, even though its hidden by the luminous body of its massive host.