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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 Masayuki
Akiyama by email.
October 8, Friday at 11:00am
"Environmental Effects on Galaxy Evolution: (plus the origin of E+A galaxies)"
Tomotsugu Goto (Johns Hopkins University)
It is a remarkable feature that properties of galaxies (color, morphology,
and luminosity) vary according to their environments. However, little
has been known on the physical origin of this variety in galaxies. We
take two approaches to tackle this problem:(i)detailed investigation on
the galaxy environment using the unprecedentedly large sample of nearby
galaxies from the Sloan Digital Sky Survey (SDSS)(ii) revealing the
evolution of the morphology-density relation since z=1 using the
Hubble Space Telescope Advanced Camera for Surveys (HST/ACS)
high-z cluster survey.
Using the SDSS data, we investigate the morphology-density relation
to find two characteristic environment where the morphology-density
relation abruptly changes (at 0.3 and 2 Rvir). The result has significant
implication for the underlying physical mechanism since it suggests that
two different mechanisms might be responsible for the morphology-density
relation. In addition, we study the environment of unusual spiral galaxies
with no [OII] or Halpha emission lines (passive spirals), and find that
passive spiral galaxies preferentially live in cluster infalling regions
(at 1-10 Rvir) Thus, a cluster related physical mechanism is likely to be
responsible for the creation of the passive spiral galaxies.
We extend these studies in the local universe to z=1 using the data
from the HST/ACS high-z cluster survey. The observed evolution of the
morphology-density relation between z=0 and 1 suggests that cluster
specific physical process is needed to explain the evolution, i.e., we found
the evidence for "nurture" scenario although this does not exclude
"nature" scenario.
In the latter half of the talk, we move focus to the E+A (post-starburst)
galaxies, which have been historically believed to be the transition objects
in the cluster galaxy evolution due to their post-starburst nature (strong
Balmer absorption lines and the lack of emission lines). In the literature,
there have been three possible explanations for E+A galaxies; (i)
cluster-related physics (e.g., ram-pressure stripping)(ii) galaxy-galaxy
merger/interaction (iii) dusty-starbursts. By constructing the largest
samples of 266 E+A galaxies from the SDSS, we observationally test these
three scenarios to reveal the physical origin of E+A galaxies.