Metallicity of Globular Clusters

Tianning LYU
  • 8 Dec '23

Dear all,

I find that in the 'globular clusters' database, there is only 'GCColor' but not metallicity data. I read Doppel+(2020), here the authors said:

Two sets of GCs are tagged, one corresponding to a more extended metal poor or ‘blue’ component, and one more concentrated and metal rich, or ‘red’ component, with relative fraction of red to blue component following observationsin Harris et al. (2015).

I don't quite understand this. It seems that the authors did not calculate the metallicity, but simply divided the globular cluster into two subsets by a ratio. Is my understanding correct? If correct, on what basis are they divided? If not correct, what is the author's method for calculating metallicity?

Thank you for help!


Jessica Doppel
  • 8 Dec '23

Dear Tianning,

Thanks for reaching out! You are correct in that we do not calculate the metallicity of the GCs in the catalog. Rather what separates the GC colors, in addition to their relative fraction of mass in the GC mass--halo mass relation, is their spatial distributions. GCs that are observed to be blue/metal poor are often more extended about their host galaxies than red/metal rich GCs in systems that show bimodality in GC colors or metallicities. The blue GCs are thus tagged to follow a more extended distribution than the red GCs.

I hope this helps!

Jess Doppel

Tianning LYU
  • 9 Dec '23

Thank you for help!

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