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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 : sseminar_at_subaru.naoj.org (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.