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The Spectroscopic and Photometric Study of a Star Cluster Sample in Andromeda Halo

Hongrui Gu, Zhou Fan, Bingqiu Chen, Xiaoying Pang, Juanjuan Ren, Ruizheng Jiang, Song Wang, Kefeng Tan, Nan Song, Chun Li, Jie Zheng, Gang Zhao, Wei Wang, Yuqin Chen, Jingkun Zhao, Haining Li, Yihan Song, Haibo Yuan, Ali Luo, Yujuan Liu, Yaqian Wu

Abstract

Halo star clusters serve as vital tracers for the formation and evolution of the Andromeda galaxy. In this work, we present physical parameters for 29 M31 halo star clusters, derived from a combination of spectroscopic and photometric data. Low-resolution spectra were acquired using the BFOSC spectrograph on the NAOC Xinglong 2.16-m telescope. For the photometric analysis, we utilized uSC and vSAGE bands from the SAGE survey, complemented by archival data from GALEX(NUV, FUV), PAN-STARRS(grizy) and the 2MASS(JHK). Ages and metallicities were determined via ULySS (Vazdekis et al. and pegase-hr) SSP model and the Bruzual & Charlot (2003) (BC03) stellar population synthesis models. The derived parameters show good agreement with literature values. Notably, for three of these clusters, this study represents the first combined photometric and spectroscopic analysis.

The Spectroscopic and Photometric Study of a Star Cluster Sample in Andromeda Halo

Abstract

Halo star clusters serve as vital tracers for the formation and evolution of the Andromeda galaxy. In this work, we present physical parameters for 29 M31 halo star clusters, derived from a combination of spectroscopic and photometric data. Low-resolution spectra were acquired using the BFOSC spectrograph on the NAOC Xinglong 2.16-m telescope. For the photometric analysis, we utilized uSC and vSAGE bands from the SAGE survey, complemented by archival data from GALEX(NUV, FUV), PAN-STARRS(grizy) and the 2MASS(JHK). Ages and metallicities were determined via ULySS (Vazdekis et al. and pegase-hr) SSP model and the Bruzual & Charlot (2003) (BC03) stellar population synthesis models. The derived parameters show good agreement with literature values. Notably, for three of these clusters, this study represents the first combined photometric and spectroscopic analysis.
Paper Structure (16 sections, 7 equations, 11 figures)

This paper contains 16 sections, 7 equations, 11 figures.

Table of Contents

  1. Introduction
  2. The Selection of Star Cluster Sample in M31 Halo
  3. Observations and Data Reduction
  4. The Spectroscopic Observations
  5. Spectral data Reduction
  6. Photometric data Reduction
  7. Archived data
  8. SAGES data
  9. Fitting with spectroscopy and the photometry of GALEX, SAGES, UBVRI, ugriz and 2MASS
  10. Fitting with BC03
  11. Fitting with ULySS
  12. Comparison between two method
  13. Comparison with other studies
  14. Discussion
  15. The UV-excess of our sample
  16. ...and 1 more sections

Figures (11)

  • Figure 1: The spatial distribution of our M31 halo star cluster sample (black dots). The dashed ellipses represent the $D_{25}$ isophotes of M31, M32, and NGC 205.
  • Figure 2: Quantum efficiency (QE) curve of the Andor iKon-L 936 BEX2-DD CCD mounted on the BFOSC instrument (red solid line). The QE exceeds 90% across most of the optical wavelength range.
  • Figure 3: Cutout images of star cluster G002 in 12 filters: GALEX(NUV, FUV); SAGES ($\rm u_{SC}$,$\rm v_{SAGES}$); Panstarrs ($g,r,i,z,y$), and 2MASS ($J,H,K$). Each panel has a field of view of 48" $\times$ 48". The red circle indicate the apertures used for photometry, optimized for signal-to-noise ratio.
  • Figure 4: Joint spectral and photometric fitting for star cluster G002 using BC03 models.Top panel: The observed spectrum (blue solid line) and photometry (blue points) overlaid with the best-fit model (gray dashed line). Horizontal error bars on photometric points represent the filter bandwidths, while vertical bars indicate photometric uncertainties.Bottom panel: The fitting residuals.
  • Figure 5: Comparison of metallicities derived from different models. The x-axis shows results from the BC03 method, while the y-axis displays results from ULySS using either the Vazdekis (V10) or pegase-hr (PEG) models. The dashed line indicates a 1:1 relation. Error bars represent the $1\sigma$ uncertainties from each method.
  • ...and 6 more figures