Extremely Metal-Poor Star-Forming Dwarf Galaxies

摘要

New deep HST/ACS photometry of the extremely metal-poor star-forming dwarf galaxy I Zw 18 is presented and compared to a similar study of its twin sister SBS 1415+437. Chemically-unevolved systems like I Zw 18 or SBS 1415+437 represent the closest analog to primordial galaxies in the early universe. It has also been argued that some of these objects (e.g., I Zw 18) may be genuine nearby 'young' galaxies. However, by revealing the existence of an evolved red stellar population in both I Zw 18 and SBS 1415+437, our HST/ACS observations do not support such an interpretation.