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A Maximum Likelihood Calibration of the Tip of the Red Giant Branch Luminosity from High Latitude Field Giants using Gaia Early Data Release 3 Parallaxes

Presentation #414.01 in the session Cosmology III.

Published onJun 29, 2022
A Maximum Likelihood Calibration of the Tip of the Red Giant Branch Luminosity from High Latitude Field Giants using Gaia Early Data Release 3 Parallaxes

The calibration of the tip of the red giant branch (TRGB) in the I-band has a direct role in determinations of the Hubble constant, a subject of recent interest. We present a maximum likelihood (ML) method designed to obtain an independent calibration of the brightness of TRGB using Gaia parallaxes from the Early Data Release 3 (EDR3) of Milky Way field Giants at high Galactic latitude. We adopt simple parameterizations for the Milky Way stellar luminosity function and density law and and optimize the likelihood of the observed sample as a function of those parameters. Using parameters to partially constrain the luminosity function from other galaxies similar to the Milky Way for which high quality TRGB data are available, we find values of the TRGB magnitude of MITRGB = -3.978 ± 0.031 (stat) ± 0.045 (sys) mag, where the systematic uncertainty covers the range of shape parameters found in our reference galaxies. While current data are insufficient to simultaneously characterize the shape of the Milky Way luminosity function we estimate that the photometry from Gaia Data Release 3 (mid-2022) will allow better constraints on the shape, and lower statistical uncertainties on the tip by a factor of 3. With expected releases of improved parallax measurements from Gaia, the method of calibrating the TRGB luminosity from field Giants is expected to reach ~ 0.01 mag uncertainty, which is an important step toward a precise TRGB-based determination of the Hubble constant.

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