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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tomonori Usuda, Kumiko S. Usuda, Naoyuki Tamura) by email : (please change"_at" to @).

December 15, Monday at 11:00 am

" A First Look at the Evolution of Brightest Cluster Galaxies beyond z=1 "

John Stott (Liverpool John Moores University)

The extreme properties of brightest cluster galaxies (BCGs) and their unique location in the centres of clusters make them powerful probes of the hierarchical galaxy formation theory in which galaxies assemble from sub-galactic size haloes. Exactly when the assemblage took place in BCGs is currently a matter of some debate. We investigate, for the first time, the evolution of these galaxies at redshifts z>1 from a small sample of X-ray bright clusters, including XMMXCSJ2215-1738, which is the most distant spectroscopically confirmed galaxy cluster at z=1.46. By comparing the K-band light with lower redshift samples, we find that overall the stellar mass of 5 BCGs between z~ 1.2-1.4 is not significantly different to the stellar mass of local counterparts. On average these BCGs are almost fully assembled 4-5 Gyrs after the big bang, having grown to 90% of their final stellar mass by this time. We demonstrate that these stellar mass estimates are relatively insensitive to the stellar population synthesis model used. BCGs hosted by the most massive clusters in semi-analytical models based on the Millennium Simulation indicate a protracted formation period over a Hubble time and predict that only 20% of the BCG stellar mass should be assembled at the epoch probed by our sample. Future large simulations and near infrared observations of galaxies in the cores of clusters from forthcoming high redshift surveys will enable us to determine whether this somewhat surprising evolutionary behavior can be reconciled with the hierarchical picture.

Seminars are also held at JAC, CFHT, and IfA.

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