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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.

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

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