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第1336回 天文学教室談話会

日時

2012年08月06日(月) 15:00

場所

大輪講室

講演者

Mr. Mohammad Akhlaghi (Astronomical Inst., Tohoku U.)

題目

Study of significant size growth of quiescent galaxies based on flux ratio analysis

要旨

Significant size evolution (SSE) in quiescent galaxies has hitherto been studied through direct measurement of the effective radius (r_e) of galaxies across cosmic history. Using the very deep Subaru Multi object infrared camera and spectrograph (MOIRCS) and Hubble space telescope Advanced camera for surveys (HST/ACS) images of the GOODS-N region, from the MOIRCS deep survey, we scrutinize the implications of both scenarios on the rest-frame V-band image of quiescent galaxies in this sample. As a conceptual departure from previous studies, r_e has not been directly measured, it has been assumed. The flux ratio analysis introduced here is based on the flux ratio of various apertures of the galaxy profile as compared to the flux ratio of the same apertures on mock profiles with known Sersic index (n). We find that if SSE is assumed, a significant evolution in n should be observed for all the quiescent galaxies from n~1.5 at z~3 to n~4 in the local universe. Such evolution is not observed if SSE is not assumed; n remains above 2.5 during cosmic history. If the local color-morphology relation with quiescent galaxies generally having n>2.5 is accepted for the high-z universe, SSE can be ruled out based on the present analysis. We don't find any correlation between galaxy age and its light concentration. Comparison of the resulting n and r_e values under both scenarios to the actual rest-frame V-band image of the galaxy shows the possible degeneracy in the measurement of these parameters in HST/ACS as well as Subaru/MOIRCS images.

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【The Colloquium Committee in 2012】
Shijun Yoshida (yoshida<at>astr.tohoku.ac.jp)
Masaki Takayama (m.takayama<at>astr.tohoku.ac.jp)
Hidetomo Honma (hide<at>astr.tohoku.ac.jp)
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