Using the Tip of the Red Giant Branch As a Distance Indicator in the Near Infrared
AffiliationUniv Arizona, Steward Observ
galaxies: distances and redshifts
Hertzsprung-Russell and C-M diagrams
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PublisherIOP PUBLISHING LTD
CitationKristen. B. W. McQuinn et al 2019 ApJ 880 63
RightsCopyright © 2019. The American Astronomical Society. All rights reserved.
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AbstractThe tip of the red giant branch (TRGB) is a well-established standard candle used to measure distances to nearby galaxies. The TRGB luminosity is typically measured in the I-band, where the luminosity has little dependency on stellar age or stellar metallicity. As the TRGB is brighter at wavelengths redder than the I-band, observational gains can be made if the TRGB luminosity can be robustly calibrated at longer wavelengths. This is of particular interest given the infrared capabilities that will be available with the James Webb Space Telescope and an important calibration consideration for using TRGB distances as part of an independent measurement of the Hubble constant. Here, we use simulated photometry to investigate the dependency of the TRGB luminosity on stellar age and metallicity as a function of wavelength (lambda 475 nm-4.5 mu m). We find intrinsic variations in the TRGB magnitude to increase from a few hundredths of a magnitude at lambda 800-900 nm to similar to 0.6 mag by lambda 1.5 mu m. We show that variations at the longer infrared wavelengths can be reduced to 0.02-0.05 mag (1%-2% accuracy in distance) with careful calibrations that account for changes in age and metal content. These represent the minimum uncertainties; observational uncertainties will be higher. Such calibration efforts may also provide independent constraints of the age and metallicity of stellar halos where TRGB distances are best measured. At 3.6 and 4.5 mu m, the TRGB magnitude is predicted to vary by similar to 0.15 mag even after corrections, making these wavelengths less suitable for precision distances.
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