Blakeslee et al., 2012, Optical and Infrared Photometry of Globular Clusters in NGC 1399: Evidence for Color–Metarllicity Nonlinearity

# 세줄요약 #

1. We combine new Wide Field Camera 3 IR Channel (WFC3/IR) F160W (H160) imaging data for NGC 1399, the central galaxy in the Fornax cluster, with archival F475W (g475), F606W (V606), F814W (I814), and F850LP (z850) optical data from the Advanced Camera for Surveys (ACS).
2. Consistent with the differing color distributions, the dependence of I814−H160 on g475−I814 for the matched GC sample is significantly nonlinear, with an inflection point near the trough in the g475−I814 color distribution.
3. these results indicate that nonlinear color–metallicity relations play an important role in shaping the observed bimodal distributions of optical colors in extragalactic GC systems.

 

# 상세 리뷰

* Author: John P. Blakeslee, Hyejeon Cho, Eric W. Peng, Laura Ferrarese, Andres Jordan, and Andre R. Martel

 

1. Introduction

• Observation: HST/WFC3(IR) Photometry to NGC 1399 GC(Globular Cluster)s.
  • g, V, I, z color is used in HST/ACS archive data.

Table 1. Summary of Observing Programs for NGC 1399 [Blakeslee et al., 2021, ApJ]

• large galaxy star formation history -> Imprinted in GC system
• GC system: bimodal distributions in optical colors.
  • -> linear relation of color-metalicity
• two GC populations
  • blue GCs(metal-poor): building block
  • red GCs(metal-rich): gas-rich major merger
• nonlinear color-metalicity relation
  • these means 'unimodal metalicity distribution at GC system
• Observation target: NGC1399(Fornax cluster)
  • 2nd near cluster(20MPC) from MW(Milky Way)

Figure 1. HST WFC3/IR F160W image of NGC 1399 (top), and the same following galaxy isophotal model and sky subtraction (bottom). [Blakeslee et al., 2021, ApJ]

 

2. Result

• The color distribution of NGC1399 GCs (Optical color v.s. Optical-Infrared color)
  • Optical color: g-I, V-I, g-z  =>  clear bimodality
  • Opt-IR color: I-H  =>  unimodal color distribution

Figure 8. Histograms of g475−I814, V606−I814, I814−H160, and V606−H160 colors for all matched GC candidates in the specified magnitude ranges and with color errors less than 0.2 magnitudes. [Blakeslee et al., 2021, ApJ]

• Optical & Opt-IR color-color relation => non linear relation.
  • color-color relation inflection point = Opt-color bimodal distribution trough.

Figure 9. The ACS+WFC3/IR I814−H160 vs. g475−I814 color–color plots. In the left panel, the individual matched GC candidates are shown, with error bars estimated from the rms images mentioned in Section 3. The red curve represents a fourth-order robust polynomial fit with coefficients given in the text. The right panel shows the median values within 10 bins (40 objects per bin) ordered by g475−I814. We also plot the same polynomial fit as in the left panel (red dashed curve), a fourth-order polynomial fit to the median points (blue curve), and a linear fit to these points (black dashed line). [Blakeslee et al., 2021, ApJ]

• Optical color GC bimodality caused by nonlinear Optical color - metallicity relation 

 

* Reference: Blakeslee, J. P., Cho, H., Peng, E. W., Ferrarese, L., Jordán, A., and Martel, A. R., “Optical and Infrared Photometry of Globular Clusters in NGC 1399: Evidence for Color-Metallicity Nonlinearity”, The Astrophysical Journal, vol. 746, no. 1, 2012. doi:10.1088/0004-637X/746/1/88.