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Peer-reviewedCC BY 4.0The Astronomical Journal

The Metal Content of Resolved Galaxies

  • Lidia N. Makarova1
  • Denis G. Purytin1,2
  • R. Brent Tully3
  • Gagandeep S. Anand4
4 affiliations
  1. 1Special Astrophysical Observatory of the Russian Academy of Sciences
  2. 2Saint Petersburg State University
  3. 3University of Hawaii
  4. 4Space Telescope Science Institute
Open at sourcePDFDOICite

Abstract

We present a homogeneous metallicity analysis of old stellar populations in the Local Volume galaxies using data from the color–magnitude diagrams/tip of the red giant branch (TRGB) catalog of the Extragalactic Distance Database ( http://edd.ifa.hawaii.edu ), which provides uniformly measured TRGB distances and point-spread function photometry for resolved stars in over 500 nearby galaxies observed with the Hubble Space Telescope. We apply the calibration of M. G. Lee et al. to estimate the mean metallicity [Fe/H] from the ( V − I ) color of the red giant branch (RGB) at M I = −3.5 mag obtaining reliable measurements for 334 galaxies out of an initial set of 558. The RGB-Colors were derived by locating the maximum stellar density in the ( M I , ( V − I )) diagram, smoothed with a Gaussian kernel and refined via Monte Carlo simulations (500–1000 realizations), yielding typical uncertainties of about 0.03 mag. Our results show that most galaxies lie within the color range ( V − I ) = 1.22−1.74 of the original calibration, corresponding to metal-poor systems typical of dwarfs, with the overall metallicity distribution peaking at [Fe/H] = −1.89 ± 0.03 dex. We find a pronounced luminosity–metallicity relation across a wide magnitude range, from faint dwarfs ( M B > −7) mag to giant galaxies ( M B < −18), described by the regression [Fe/H] = −2.6−0.075 M B . At the same time, on the luminosity–metallicity plane, dwarf spheroidals occupy the higher-metallicity region, which may reflect the age–metallicity degeneracy in RGB-based metallicity determinations. Both dwarf and giant galaxies follow the same relation, though ACS fields for giants often sample outer, more metal-poor regions.

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Cite

BibTeXRIS
BibTeX
@article{makarova2026metal,
  title = {{The Metal Content of Resolved Galaxies}},
  author = {Lidia N. Makarova and Denis G. Purytin and R. Brent Tully and Gagandeep S. Anand},
  journal = {The Astronomical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-3881/aea78c},
  url = {https://iopscience.iop.org/article/10.3847/1538-3881/aea78c},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - The Metal Content of Resolved Galaxies
AU  - Lidia N. Makarova
AU  - Denis G. Purytin
AU  - R. Brent Tully
AU  - Gagandeep S. Anand
PY  - 2026
DA  - 2026/10/09
JO  - The Astronomical Journal
DO  - 10.3847/1538-3881/aea78c
UR  - https://iopscience.iop.org/article/10.3847/1538-3881/aea78c
AB  - We present a homogeneous metallicity analysis of old stellar populations in the Local Volume galaxies using data from the color–magnitude diagrams/tip of the red giant branch (TRGB) catalog of the Extragalactic Distance Database ( http://edd.ifa.hawaii.edu ), which provides uniformly measured TRGB distances and point-spread function photometry for resolved stars in over 500 nearby galaxies observed with the Hubble Space Telescope. We apply the calibration of M. G. Lee et al. to estimate the mean metallicity [Fe/H] from the ( V − I ) color of the red giant branch (RGB) at M I = −3.5 mag obtaining reliable measurements for 334 galaxies out of an initial set of 558. The RGB-Colors were derived by locating the maximum stellar density in the ( M I , ( V − I )) diagram, smoothed with a Gaussian kernel and refined via Monte Carlo simulations (500–1000 realizations), yielding typical uncertainties of about 0.03 mag. Our results show that most galaxies lie within the color range ( V − I ) = 1.22−1.74 of the original calibration, corresponding to metal-poor systems typical of dwarfs, with the overall metallicity distribution peaking at [Fe/H] = −1.89 ± 0.03 dex. We find a pronounced luminosity–metallicity relation across a wide magnitude range, from faint dwarfs ( M B > −7) mag to giant galaxies ( M B < −18), described by the regression [Fe/H] = −2.6−0.075 M B . At the same time, on the luminosity–metallicity plane, dwarf spheroidals occupy the higher-metallicity region, which may reflect the age–metallicity degeneracy in RGB-based metallicity determinations. Both dwarf and giant galaxies follow the same relation, though ACS fields for giants often sample outer, more metal-poor regions.
SN  - 0004-6256
SN  - 1538-3881
ER  -