紀要論文

STUDY OF THE FORMATION MECHANISM OF URSA MINOR DWARF SPHEROIDAL GALAXY USING SUBARU/HSC WIDE FIELD DATA

すばる望遠鏡/HSCで探るこぐま座矮小楕円体銀河の形成メカニズム

eng

24368083

https://doi.org/10.15002/00030772

法政大学大学院理工学研究科

法政大学大学院紀要. 理工学研究科編

65

1

8

2024-03-24

Version of Record

We investigate the star formation history of Ursa Minor dwarf spheroidal galaxy (UMi dSph) to address its formation mechanism from the analysis of color-magnitude diagram (CMD) using the g- and i-band wide field data observed by Hyper Suprime-Cam on the Subaru Telescope (Subaru/HSC). The method is based on the hybrid genetic algorithm (HGA) combining annealing and genetic algorithm to minimize a 𝜒^2 merit function by comparing the observed CMD and synthetic CMD of simple stellar populations. The estimated Age-Metallicity Relations (AMRs) indicate that over 90% of star formation was completed before z = 2, and found the multiple populations suggested in a previous spectroscopic study which found both metal-rich population ([Fe⁄H] = −2.0) and metal-poor population ([Fe⁄H] = −2.3). We found that these populations formed simultaneously 12 Gyr ago. We also discovered the metal-poorer population ([Fe⁄H] = −2.7) which was detected beyond 2 times the half-light radius, and the main sequence stars located beyond the tidal radius. These populations suggest the existence of a stellar halo of UMi dSph. From these results, it is suggested that UMi dSph should have experienced a few minor mergers in the past.

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