A 1.3% Distance to M33 from Hubble Space Telescope Cepheid Photometry

Abstract

We present a low-dispersion period–luminosity relation (PL) based on 154 Cepheids in Messier 33 (M33) with Hubble Space Telescope (HST) photometry from the PHATTER survey. Using high-quality ground-based light curves, we recover Cepheid phases and amplitudes for multi-epoch HST data and we perform template fitting to derive intensity-averaged mean magnitudes. HST observations in the SH0ES near-infrared Wesenheit system significantly reduce the effect of crowding relative to ground-based data, as seen in the final PL scatter of σ = 0.11 mag. We adopt the absolute calibration of the PL based on HST observations in the Large Magellanic Cloud and a distance derived using late-type detached eclipsing binaries to obtain a distance modulus for M33 of μ = 24.622 ± 0.030 mag (d = 840 ± 11 kpc), a best-to-date precision of 1.3%. We find very good agreement with past Cepheid-based measurements. Several tip of the red giant branch estimates bracket our result while disagreeing with each other. Finally, we show that the flux contribution from star clusters hosting Cepheids in M33 does not impact the distance measurement and we find only ∼3.7% of the sample is located in (or nearby) young clusters. M33 offers one of the best sites for the cross-calibration of many primary distance indicators. Thus, a precise independent geometric determination of its distance would provide a valuable new anchor to measure the Hubble constant.

Subaru Suprime-Cam Wide-field BVI Stellar Photometry of the M33 Galaxy

“…The high quality of the RGB star photometry data (Figure 5(h)) suggested using the TRGB method for distance determination to the M33 galaxy. Actually, even the most accurate distance moduli of M33, which were recently determined based on the TRGB (Lee et al 2022) and Cepheid (Breuval et al 2023) methods, differ by 0.1 mag. The differences of galaxy distances determined using these two methods are comprehensively discussed by Madore & Freedman (2024).…”

“…Lee et al (2022) determined the true distance modulus of M33 using the I-passband TRGB method to be equal to 24.72 ± 0.02 stat ± 0.07 syst . Breuval et al (2023) determined the true distance modulus of M33 based on the Cepheid method to be equal to 24.622 ± 0.030. Therefore, the true distance modulus derived in the present study (24.63) falls between these values and is closer to the result based on Cepheids.…”

“…Recent enhanced interest in the M33 disk stellar populations is due to the survey conducted using the Hubble Space Telescope (HST; Williams et al 2021;Lazzarini et al 2022;Smercina et al 2023) and extensive spectroscopic studies by Gilbert et al (2022) and Quirk et al (2022). Also, the M33 galaxy recently became an important reference point for extragalactic distance calibrations (Lee et al 2022;Breuval et al 2023). Therefore, we decided to make available for the community the results of Subaru stellar photometry survey covering the entire M33 galaxy disk (Figure 1).…”