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THE NON-LINEARITY EFFECT ON THE COLOR-TO-METALLICITY CONVERSION OF GLOBULAR CLUSTERS IN NGC 5128

  • KIM, HAK-SUB (Department of Astronomy & Center for Galaxy Evolution Research, Yonsei University) ;
  • YOON, SUK-JIN (Department of Astronomy & Center for Galaxy Evolution Research, Yonsei University)
  • Received : 2014.11.30
  • Accepted : 2015.06.30
  • Published : 2015.09.30

Abstract

The metallicity distribution of globular clusters (GCs) provides a crucial clue for the star formation history of their host galaxy. With the assumption that GCs are generally old, GC colors have been used as a proxy for GC metallicities. Bimodal color distributions of GCs observed in most large galaxies have, for decades, been interpreted as bimodal metallicity distributions, indicating the presence of two populations within a galaxy. However, the conventional view has been challenged by a new theory that non-linear GC color-metallicity relations can cause a bimodal color distribution even from a single-peaked metallicity distribution. Using photometric and spectroscopic data of NGC 5128 GCs in combination with stellar population simulation models, we examine the effect of non-linearity in GC color-metallicity relations on transformation of the color distributions into the metallicity distributions. Although in some colors offsets are present between observations and models for the color-metallicity relations, their overall shape agrees well for various colors. After the offsets are corrected, the observed spectroscopic metallicity distribution is well reproduced via modeled color-metallicity relations from various color distributions having different morphologies. We discuss the implications of our results.

Keywords

References

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