Strong Lensing Analysis of the Galaxy Cluster MACS J1319.9+7003 and the   Discovery of a Shell Galaxy
  We present a strong-lensing (SL) analysis of the galaxy cluster MACS J1319.9+7003 ($z=0.33$, also known as Abell 1722), as part of our ongoing effort to analyze massive clusters with archival {\it HST} imaging. We spectroscopically measured with Keck/MOSFIRE two galaxies multiply-imaged by the cluster. Our analysis reveals a modest lens, with an effective Einstein radius of $\theta_{e}(z=2)=12\pm1$", enclosing $2.1\pm0.3\times10^{13}$ $M_{\odot}$. We briefly discuss the SL properties of the cluster, using two different modeling techniques, and make the mass models publicly-available\footnote{ftp://wise-ftp.tau.ac.il/pub/adiz/MACS1319/}. Independently, we identified a noteworthy, young Shell Galaxy (SG) system forming around two likely interacting cluster members, 20" north of the BCG. SGs are rare in galaxy clusters, and indeed, a simple estimate yields that they are only expected in roughly one in several dozen, to several hundred, massive galaxy clusters (the estimate can easily change by an order-of-magnitude within a reasonable range of characteristic values relevant for the calculation). Taking advantage of our lens model best-fit, mass-to-light scaling relation for cluster members, we infer that the total mass of the SG system is $\sim1.3\times10^{11}$ M$_{\odot}$, with a host-to-companion mass ratio of about 10:1. Despite being rare in high density environments, the SG constitutes an example to how stars of cluster galaxies are being efficiently redistributed to the Intra Cluster Medium. Dedicated numerical simulations for the observed shell configuration, perhaps aided by the mass model, might cast interesting insight on the interaction history and properties of the two galaxies. An archival HST search in galaxy cluster images can reveal more such systems. 
Adi Zitrin
astro-ph.GA