The Origin of the Virgo Intergalactic Population

The intracluster light (ICL) is a major component of galaxy clusters, and contains a record of the galaxies destroyed during hierarchical assembly of the cluster. This proposal addresses three issues critical to understanding the origin and evolution of intergalactic populations, using resolved star WFC3/IR photometry of intergalactic fields in the Virgo cluster. Foremost, we will probe the age distribution of Virgo's intracluster stars via the period distribution of bright AGB variable stars, a tool successfully deployed to study stellar populations in elliptical galaxies. By spreading the observations over 8 epochs and two HST cycles (4+4), we can determine periods and reveal the age spread of the intracluster stars, opening a new window on their origin and evolution. Second, IR color magnitude diagrams from the stacked imaging will establish the metallicity distribution function of the ICL, constraining the luminosity function and abundances of the galaxies that have been dismembered in assembling the intracluster population. Third, by observing five fields around the core of the cluster, we will trace how spatially well-mixed the ICL population is and how its age and metallicity vary across diverse environments, and thus measure its evolutionary state. While JWST will extend photometric work on the Virgo ICL, period determination of LPVs with JWST is very difficult because of its restricted visibility window in Virgo. It is therefore critical to begin these multi-cycle observations while time permits before the end of HST's lifetime.