# A Gaia Data Release 3 View on the Tip of the Red Giant Branch Luminosity

**Authors:** Siyang Li, Stefano Casertano, Adam G. Riess  
**arXiv:** [2304.06695](https://arxiv.org/abs/2304.06695)  
**Date:** 2023-04-13  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.06695v1/

## Key points

- Siyang Li, Stefano Casertano, and Adam G. Riess explore how to refine the determination of the Hubble constant using the tip of the red giant branch (TRGB) as a standard candle.
- They use $Gaia$ Data Release 3 (DR3) to directly calibrate the luminosity of the TRGB in the Johnson-Cousins I band.
- The authors calibrate the TRGB luminosity using a two-dimensional maximum likelihood algorithm with field stars and $Gaia$ synthetic photometry and parallaxes.
- They find that for a high-contrast and low-contrast break characterized by either values of the contrast parameter $R$ or magnitude of break $\beta$, respectively, $M^{TRGB}_I = -4.02$ and $-3.92$ mag respectively, or a midpoint of $-3.970 \pm 0.042_{-0.024}$ (sys) $\pm 0.062$ (stat) mag.
- This measurement improves upon previous TRGB measurements as higher precision photometry based on $Gaia$ DR3 allows them to constrain two additional free parameters of the luminosity function.
- The authors investigate whether they can use $Gaia$ DR3 synthetic photometry to calibrate TRGB luminosity with $\omega$ Centauri but find evidence of blending within its inner region for cluster member photometry that precludes accurate calibration with $Gaia$ DR3 photometry.
- Instead, they provide an updated TRGB measurement of $m^{TRGB}_I = 9.82 \pm 0.04$ mag in $\omega$ Centauri using ground-based photometry from the most recent version of the database described in Stetson et al. (2019), which gives $M^{TRGB}_I = -3.97 \pm 0.04$ (stat) $\pm 0.10$ (sys) mag when tied to the $Gaia$ EDR3 parallax distance from consensus estimates provided by Vasiliev & Baumgardt (2021), Soltis et al. (2021), and Ma\'{i}z Apell\'{a}niz et al.(2022a).

## Summary

In their paper, "A Gaia Data Release 3 View on the Tip of the Red Giant Branch Luminosity," Siyang Li, Stefano Casertano, and Adam G. Riess explore how to refine the determination of the Hubble constant using the tip of the red giant branch (TRGB) as a standard candle. They use $Gaia$ Data Release 3 (DR3), which 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 it is least sensitive to metallicity. The authors calibrate the TRGB luminosity using a two-dimensional maximum likelihood algorithm with field stars and $Gaia$ synthetic photometry and parallaxes. They find that for a high-contrast and low-contrast break characterized by either values of the contrast parameter $R$ or magnitude of break $\beta$, respectively, $M^{TRGB}_I = -4.02$ and $-3.92$ mag respectively, or a midpoint of $-3.970 \pm 0.042_{-0.024}$ (sys) $\pm 0.062$ (stat) mag. This measurement improves upon previous TRGB measurements as higher precision photometry based on $Gaia$ DR3 allows them to constrain two additional free parameters of the luminosity function. The authors also investigate whether they can use $Gaia$ DR3 synthetic photometry to calibrate TRGB luminosity with $\omega$ Centauri but find evidence of blending within its inner region for cluster member photometry that precludes accurate calibration with $Gaia$ DR3 photometry. Instead, they provide an updated TRGB measurement of $m^{TRGB}_I = 9.82 \pm 0.04$ mag in $\omega$ Centauri using ground-based photometry from the most recent version of the database described in Stetson et al. (2019), which gives $M^{TRGB}_I = -3.97 \pm 0.04$ (stat) $\pm 0.10$ (sys) mag when tied to the $Gaia$ EDR3 parallax distance from consensus estimates provided by Vasiliev & Baumgardt (2021), Soltis et al. (2021), and Ma\'{i}z Apell\'{a}niz et al.(2022a).