Star formation history in the Magellanic clouds: X-ray observations of stellar remnants

Abstract

The Advanced Satellite for Cosmology and Astrophysics (ASCA) has observed a significant fraction of the Magellanic Clouds (MCs). All the available ASCA data on the MCs were systematically analyzed, and a simple method of source classification was established according to a hardness ratio of each source. The candidates of X-ray Binary Pulsars (XBPs) and thermal Supernova Remnants (SNRs) were defined with this method, and the source populations in the MCs and the Galaxy were compared. It was found that the number density of High-Mass X-ray Binaries (HMXBs) and candidates is extremely high in the SMC (Small MC), while Low-Mass X-ray Binaries (LMXBs) are very rare in the MCs. Based on these results, possible implications on the star formation history in the MCs are discussed.

第15号科学衛星「あすか」(ASCA)により、マゼラン星雲(MC)のかなりな部分が観測された。得られている全ての「あすか」のMCに関するデータを系統的に解析し、各X線源天体の硬度比に基づき、X線源を分類する簡便な方法を構築した。この方法に基づいて、X線連星パルサ(XBP)と熱的超新星残骸(SNR)の候補天体を選びだし、それぞれの天体数をマゼラン星雲(MC)と銀河系とで比較した。その結果、小マゼラン星雲においては大質量X線連星(HMXBs)とその候補の個数密度が銀河系に比べ非常に高くなっているが、小質量X線連星(LMXBs)は大小マゼラン星雲で非常に稀であることが判明した。この結果に基づき、マゼラン星雲での星生成史について考えられる推測を論じた。