RUI: Clocking the formation of today's largest galaxies: Wide Field Integral Spectroscopy of Brightest Cluster Galaxies and their surroundings

California Polytechnic State University Foundation, San Luis Obispo CA

Investigators

Abstract

Mass in the universe is not smoothly distributed. Maps of nearby galaxies show that they are clustered and that these clusters are separated by large voids, where little matter is present. Each cluster has one galaxy that is the brightest. Curiously, these Brightest Cluster Galaxies (BCGs) are often found at the center of their host cluster, and often contain the oldest and reddest stars around. One outstanding question in the field of extragalactic astronomy is the following: How and when do galaxies build-up their mass? This project will measure the ages and chemical compositions of BCGs from their cores to their outskirts. It will also calculate how long it would take a BCG to grow by merging with nearby systems. The results will help astronomers discriminate between various galaxy evolution scenarios. Imaging spectroscopy (IFU) of 25 local cluster galaxies and their nearby companions will be collected and analyzed. In addition to doubling the sample of IFU studied BCGs and companions, wide field observations obtained from this work represent the first spectroscopic study of a sample of intra-cluster light (ICL). Focusing on the local universe means that its components can be studied in exquisite detail. To help elucidate the nature of the BCG and its formation, the objectives for the period of proposed work are to determine mechanisms and timescales that govern stellar mass build-up in the sample. The main deliverables include: 1) Maps of the kinematic properties and stellar populations of the BCGs, the close companions and the ICL. The location of the oldest and youngest stars within the galaxies can lend credence to whether or not the galaxies formed inside out. Whether the BCG is coeval with the intra-cluster light can be determined if the two have similar stellar populations, and if the surface brightness profile breaks; 2) Estimates of the timescale and relative contribution to the recent stellar mass buildup of BCGs and the ICL from major and minor mergers; 3) Constraints on the amount of any new or ?in situ? stellar mass buildup. This can be determined by examining the stellar populations, from searching for wet minor merging, or looking for cooling from a hot halo. Determining the properties of these local systems will provide powerful constraints for cosmological models and will form an important comparison sample for higher-redshift BCGs already being compiled. Undergraduates will be heavily involved in every aspect of this project. Through performing their research with cutting edge data, visiting a national observatory site, and presenting their work to colleagues they will experience training in the technical and social skills required to enter STEM fields as graduate students or in industry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.