Globular clusters as probes of galaxy evolution

NGC 5128

Sukyoung Yi, E. Peng, H. Ford, S. Kaviraj, Seok-Jin Yoon

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

We present the results of our analysis of the photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated colour U - B can be an effective metallicity indicator for simple stellar populations. This is because it is sensitive to metallicity via the opacity effect but relatively insensitive to the effective main-sequence turn-off temperature of the population (and thus to age) when T eff ≈ 7000-12 000 K, that is, when the Balmer Jump is strong. This flat U - B versus T eff relation is a result of the fact that the blueing effect of the optical continuum with increasing temperature is temporarily stopped by the Balmer Jump, which becomes greater with temperature in this range. In this study we use U - B and B - V as metallicity and age indicators, respectively. We first show that the use of the U - B versus B - V two-colour diagram roughly yields the metallicities and ages of the Milky Way globular clusters independently determined, and then apply the technique to the clusters in NGC 5128. There is a large range in U - B, which corresponds to [Fe/H] of from -2.0 to over +0.3. The large uncertainties from the data and the models currently prevent us from pinning down their ages and metallicities. Although a constant age for all these clusters cannot be ruled out, there is a hint of the metal-rich clusters being younger. Significance of these results and caveats of the analysis are discussed.

Original languageEnglish
Pages (from-to)1493-1499
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume349
Issue number4
DOIs
Publication statusPublished - 2004 Apr 21

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globular clusters
metallicity
probe
galaxies
probes
color
temperature
elliptical galaxies
metal clusters
opacity
diagram
diagrams
continuums
metal
effect
indicator
analysis

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science

Cite this

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title = "Globular clusters as probes of galaxy evolution: NGC 5128",
abstract = "We present the results of our analysis of the photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated colour U - B can be an effective metallicity indicator for simple stellar populations. This is because it is sensitive to metallicity via the opacity effect but relatively insensitive to the effective main-sequence turn-off temperature of the population (and thus to age) when T eff ≈ 7000-12 000 K, that is, when the Balmer Jump is strong. This flat U - B versus T eff relation is a result of the fact that the blueing effect of the optical continuum with increasing temperature is temporarily stopped by the Balmer Jump, which becomes greater with temperature in this range. In this study we use U - B and B - V as metallicity and age indicators, respectively. We first show that the use of the U - B versus B - V two-colour diagram roughly yields the metallicities and ages of the Milky Way globular clusters independently determined, and then apply the technique to the clusters in NGC 5128. There is a large range in U - B, which corresponds to [Fe/H] of from -2.0 to over +0.3. The large uncertainties from the data and the models currently prevent us from pinning down their ages and metallicities. Although a constant age for all these clusters cannot be ruled out, there is a hint of the metal-rich clusters being younger. Significance of these results and caveats of the analysis are discussed.",
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Globular clusters as probes of galaxy evolution : NGC 5128. / Yi, Sukyoung; Peng, E.; Ford, H.; Kaviraj, S.; Yoon, Seok-Jin.

In: Monthly Notices of the Royal Astronomical Society, Vol. 349, No. 4, 21.04.2004, p. 1493-1499.

Research output: Contribution to journalArticle

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AB - We present the results of our analysis of the photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated colour U - B can be an effective metallicity indicator for simple stellar populations. This is because it is sensitive to metallicity via the opacity effect but relatively insensitive to the effective main-sequence turn-off temperature of the population (and thus to age) when T eff ≈ 7000-12 000 K, that is, when the Balmer Jump is strong. This flat U - B versus T eff relation is a result of the fact that the blueing effect of the optical continuum with increasing temperature is temporarily stopped by the Balmer Jump, which becomes greater with temperature in this range. In this study we use U - B and B - V as metallicity and age indicators, respectively. We first show that the use of the U - B versus B - V two-colour diagram roughly yields the metallicities and ages of the Milky Way globular clusters independently determined, and then apply the technique to the clusters in NGC 5128. There is a large range in U - B, which corresponds to [Fe/H] of from -2.0 to over +0.3. The large uncertainties from the data and the models currently prevent us from pinning down their ages and metallicities. Although a constant age for all these clusters cannot be ruled out, there is a hint of the metal-rich clusters being younger. Significance of these results and caveats of the analysis are discussed.

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