高紅移大質量星系的形成機制至今仍無定論。在星系形成的層級理論(hierarchical theory) 中，大質量星系的形成是由長時間的質量累積所成，因此其生成的時間通常會被認為是在星系演化的晚期。然而近年的觀測研究發現，有一些大質量星系在宇宙早期已經形成，這樣的結果違反了層級理論的假設。本研究的目的在於尋找更多高紅移的大質量星系來檢視各種星系形成的理論的可能性。我們使用了HSC 的觀測資料來計算其觀測範圍內星系的質量。我們利用光譜能量分布擬合(SED fitting) 將樣本分類為不同類型的星系，並校正了紅移的影響(K-correction)，再使用質量-光度關係式來估計星系的恆星質量。這項研究的結果中，我們找到了一批可能的大質量星系，這些星系分布在紅移2.3 < z < 2.8 處，擁有質量M > 10^13 M⊙，且主要是由氣體含量較少的星系所組成。這個結果支持了認為一些特大質量星系是在宇宙早期形成的downsizing 理論。;The formation of the massive galaxies at high redshift is still unclear. In the hierarchical formation paradigm, massive galaxies should appear at late epochs of galaxy evolution due to long-time accretion of mass. However, recent observations have found massive galaxies at high redshifts, which seem to be unusual for the common hypothesis. In this work, we tried to find the most massive galaxies at high redshifts. We used the photometric data of Hyper-Surprime Cam (HSC) to derive the stellar masses of galaxies in HSC-SSP pdr1 Deep survey. We classified our sample into different galaxy types and performed the K-correction by SED fitting, and used mass-luminosity relations to estimate the stellar mass of galaxies. In the results, we selected candidates for massive galaxies with M > 10^13 M⊙. These massive candidates are dominated by gas-poor dry galaxies in the redshift range of 2.3 < z < 2.8. The results support a downsizing scenario, which suggests that some of the most massive galaxies formed at the early universe.
