# 세줄 요약 #
- Use Optical and NIR photometry of M60 GC system to examine the GC color distribution morphologies.
- Through Optical color & Opt-NIR color relation, we try to deduce the exact shape of CMR, then We use YEPS model to derive the metallicity distribution function (MDF) & color-metallicity relation (CMR) of NGC 4649 GC (* Why NIR Observation? ⇒ directly measures the metallicity of GCs).
- Our results support the recent claim that the optical color bimodality observed in early-type galaxies is caused by the nonlinear nature of their color–metallicity relations.
# 상세 리뷰 #
1. Introduction: Color Bimodality
- Color distributions of globular clusters (GCs) in most massive galaxies are bimodal.
- Two different views!: 1) Two GC subpopulations [*Brodie & Strader 2006], 2) Non-linear color-metallicity relation (CMR) [*Yoon, Yi & Lee 2006]
- This debate has lasted for over a decade, with more than 300 SCI papers with color bimodality as keywords.
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2. Observational Data
- Target: Elliptical Galaxy M60 (NGC4649): The third-brightest giant elliptical galaxy of the Virgo cluster of galaxies [*Distance = 16.8 ± 1.2 Mpc (Mey et al. 2007) / *Morphological type = E2]
- Observation Information
- Instrument: Subaru/MOIRCS
- Observation date: 2008-04-22
- Wavelength: Ks-band (NIR)
- Data Reduction: MCSRED (IRAF package)
- Ellipse fitting: ELLIPSE & BMODEL (IRAF)
- Photometry: IRAF/DAOPHOT
- Matching with optical band data
- HST/ACS (Strader et al. 2012) : g, z band data / GC candidates number = 1603
- Gemini/GMOS (Faifer et al. 2012) : g, r, i band data / GC candidates number = 1546
- The GCs matched with all optical band catalog: g, r, i, z, Ks band data / GC candidates number = 769
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3. Results
- Color Distribution: In Opt-NIR color, bimodality is weakened! ➜ Nonlinear CMR?
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- Color-color Relations: 1) Colors behave differently as a function of metallicity. 2) The relations between different color indices give Information on the color-metallicity relation
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- Metallicity Distribution Function: 1) The stellar population model does not fit well in Optical color & opt-NIR color plot. 2) Use YEPS model to derive the metallicity distribution function (MDF) in Optical color-color plot. 3) Then, the obtained metallicity distribution is converted into color by using the YEPS model.
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# Reference:
- [학위논문] 정종훈, NIR Color-Metallicity Relations and Color Distributions of Globular Clusters in Elliptical Galaxy NGC 4649 with Subaru/MOIRCS, 연세대학교, 일반대학원 학위논문, 2018.
- [국제학회] Jong-Hoon Jeong, Sooyoung Kim, Suk-Jin Yoon, NIR Color–Metallicity Relations and Color Distributions of Globular Cluster system in Elliptical Galaxy NGC 4649 with Subaru/MOIRCS, IAUGA (General Assembly International Astronomical Union), 2018
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