Milky Way field red giant branch stars from Gaia DR3

Gaia Data Release 3 (DR3) provides synthetic photometry constructed from low-resolution BP/RP spectra for Milky Way field stars that can be used to directly calibrate the luminosity of the TRGB in the Johnson-Cousins I band, where the TRGB is least sensitive to metallicity. We calibrate the TRGB luminosity using a two-dimensional maximum likelihood algorithm with field stars and Gaia synthetic photometry and parallaxes.

For a high-contrast and low-contrast break (characterized by the values of the contrast parameter R or the magnitude of the break {beta}), we find M^TRGB^_I_=-4.02 and -3.92mag respectively, or a midpoint of -3.970_-0.024_^+0.042^(sys)+/-0.062(stat)mag. This measurement improves upon the TRGB measurement from Li+ (2022, J/ApJ/939/96), as the higher precision photometry based on Gaia DR3 allows us to constrain two additional free parameters of the luminosity function.