Recent star formation history of the central giant elliptical galaxy in the cluster MACS J0329.7-0211

Abstract

The Cluster Lensing and Supernova survey with Hubble (CLASH) program imaged 25 massive clusters in 16 broadband filters spanning the near-UV to near-IR. This program provides an unprecedented opportunity to investigate how precisely one can infer stellar properties - ages and metallicities - by fitting theoretical spectra from stellar population syntheses to spatially-resolved spectral energy distributions (SEDs) spanning a very broad wavelength range. Here, I apply this method to study recent star formation in the central giant elliptical galaxies of CLASH clusters that exhibit spatially extended UV emission. Those that reside in virialized clusters where the temperature of the intracluster X-ray gas decreases towards the cluster center preferential exhibit luminous optical line-emitting gas and star formation, implicating cooling of the intracluster gas for the recent star formation. If so, then the star formation in these galaxies should be extended not just over space but also over time, and have a metallicity resembling that of the intracluster gas.

In my thesis, I examine the nature and cause of star formation in the BCG of the cluster MACS J0329.7-0211 , one of the clusters observed in the CLASH program. To extract the SEDs of the young stellar population, I first fitted an accurately determined 2-dimensional models to the light distribution of the old stellar population. Subtracting this model from the images in each filter, I then extracted the spectral energy distribution (SED) of the young stellar population along each spatially resolved sightline. This approach simplifies model fitting of the SEDs, rather than to having to simultaneously fit SEDs to the old and young stellar populations simultaneously as adopted in previous works on the BCGs in the CLASH program.

I then examined the spatially-resolved SEDs using different tools: (i) color-color diagrams; and (ii) chi-square minimization fit (with and without dust extinction). I find the younger stellar population in this galaxy to have ages spanning the range from $<10$ Myr to $\sim100$ Myr; with comparable SFR over the past 100 Myr; and having a decreasing SFR and mass as a function of radial distance. These are features consistent for stars forming from cooled intracluster gas. This thesis, however, cannot place constraint on the metallicity of the younger stellar population. My thesis provides a proof-of-work for what can be learn about star formation in elliptical galaxies - comprising the relatively simple case of a younger stellar population projected against an old stellar population - from high quality broadband images spanning a wide wavelength range.