STRONG LENSING ANALYSIS OF THE GALAXY CLUSTER MACS J1319.9+7003 AND THE DISCOVERY OF A SHELL GALAXY Academic Article uri icon

abstract

  • We present the first strong-lensing analysis of the massive 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 Hubble Space Telescope imaging. We identified and spectroscopically measured with Keck/MOSFIRE two galaxies multiply-imaged by the cluster. Our lensing analysis reveals a modest lens, with an effective Einstein radius of θe(z = 2) = 12"1, enclosing 2.1±0.3 x 10^(13) M_☉. We brie y discuss the strong-lensing properties of the cluster, using two different modeling techniques, and make the mass models publicly-availablea. Independently, we identifieed a noteworthy, young Shell Galaxy system forming around two likely interacting cluster members, 2000 north of the Brightest Cluster Galaxy (BCG), with the smaller companion only 0.66" (~3 kpc in projection) from the host galaxy's core. Shell galaxies 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). While we assume the shell galaxy is in the cluster as is also evident from its colors, we also acknowledge that spectroscopic redshifts might be needed to further secure the nature of the system. Taking advantage of our lens model best-fit, mass-to-light scaling relation for cluster members, we infer that the total mass of the shell galaxy system is 1.3 x 10^(11) M_☉, with a host-to-companion mass ratio of about 10:1. Despite being rare in high density environments, the shell galaxy 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 might reveal more such systems, whose rate would be interesting to compare to our estimate.

publication date

  • January 1, 2017