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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, Masayuki Akiyama)
by email : sseminar_at_subaru.naoj.org (please change"_at" to @).
August 30, Wednesday at 11:30am
" Spitzer Observations of the Brightest Galaxies in X-Ray-Luminous Clusters: Implications for Cluster Cooling Flows "
Eiichi Egami
(Steward Observatory, University of Arizona)
In the cores of X-ray-luminous clusters of galaxies, estimated
radiative gas cooling times are often significantly shorter than the
Hubble time, suggesting the possibility that these clusters sustain a
flow of cooling gas accreting onto the brightest cluster galaxy (BCG)
at the cluster center (i.e., a cluster cooling flow). I will present
the results from our Spitzer cluster program, showing that the BCGs
located in clusters with an extremely short gas cooling time (< 1 Gyr)
are IR-luminous, which is consistent with the idea that a cluster
cooling flow is triggering the infrared activity in these BCGs.
Judged from the Spitzer/IRS spectrum taken for one such IR-luminous
BCG, the source of the infrared luminosity is star formation (e.g.,
strong PAH emission). Furthermore, the spectrum shows abnormally
strong pure-rotational molecular hydrogen (H2) emission lines (likely
shock-excited) with a corresponding warm H2 gas mass of 10^{10} Msun,
the largest known to date. Together, these results indicate that the
BCGs in strongly cooling cluster cores are unusually active, and
suggest that their IR properties are intimately connected to the
intracluster gas cooling process.
I will also describe briefly another on-going Spitzer cluster project
to study gravitationally lensed high-redshift galaxies.