紅色星系形態分佈

Abstract

我們使用MEGACAM呈現的DEEP2場域影像資料，研究星系的型態分佈。透過模擬以了解MEGACAM影像中雜訊的影響，並藉由此結果作為星系樣本的篩選。被挑選的樣本包含了212個絕對光度U-B > 0.2的紅色星系，以及175個U-B < 0.2的藍色星系，且所有星系皆分佈在0.6 ~ 1.1的紅位移範圍內。我們使用分析軟體GALFIT以及表面亮度的色西模型，來模合星系的最適符合表面亮度輪廓，並且根據色西指數n的大小將星系作分類，分界點為n = 2.5。紅色星系的組成主要為結構以核球為主的星系，然而有大約1/5的紅色星系為結構以圓盤為主、且為觀測上面向的星系，我們稱之為擴散紅色星系。紅色星系被分為三類：核球為主的星系、側向的盤狀星系以及擴散星系。這些星系的色西指數隨著紅位移的減少而增大，以及星系質量隨著色西指數增大而增大，這個結果與Hierarchical 星系形成模型以及其他的研究結果相符。

We study the morphology distribution of galaxies, using the galaxy samples of CFHT MEGACAM DEEP2 data. The samples are selected via the simulation result which presents the effect of MEGACAM image noise. The selected sample includes 212 red galaxies with rest-frame color U-B > 0.2 and 175 blue galaxies with U-B < 0.2; and with redshift within 0.6 < z < 1.1. We use the fitting code GALFIT to fit the surface brightness profile of galaxies with the single Sérsic model and parametric those via the Sérsic index n with a division at n = 2.5. Red galaxies mainly consist of bulge- dominated objects, while around 1/5 of those presents disk-dominated profile but observationally face-on, so-called diffuse red galaxies. We divide red galaxies into three groups: bulge-dominated galaxies, edge-on disk galaxies, and diffuse red galaxies. The samples bias higher Sérsic indices towards low z; and greater stellar mass towards high n. This is consistent with the Hierarchical forming model and presented by other investigations.