M31 PAndromeda Cepheid sample observed in four HST bands

TL;DR

This study presents the largest HST-based Cepheid sample in M31 across four bands, analyzing Period-Luminosity relations and their implications for the Hubble constant with minimal dispersion.

Contribution

It provides the largest catalog of Cepheids in M31 with multi-band HST data and investigates the impact of sample selection on the Period-Luminosity relation and Hubble constant.

Findings

Small dispersion in Period-Luminosity relations (e.g., 0.138 mag in F160W)

No broken slope in the overall Period-Luminosity relations

Sample selection affects the detection of broken slopes and Hubble constant estimates

Abstract

Using the M31 PAndromeda Cepheid sample and the HST PHAT data we obtain the largest Cepheid sample in M31 with HST data in four bands. For our analysis we consider three samples: A very homogeneous sample of Cepheids based on the PAndromeda data, the mean magnitude corrected PAndromeda sample and a sample complementing the PAndromeda sample with Cepheids from literature. The latter results in the largest catalog with 522 fundamental mode (FM) Cepheids and 102 first overtone (FO) Cepheids with F160W and F110W data and 559 FM Cepheids and 111 FO Cepheids with F814W and F475W data. The obtained dispersion of the Period-Luminosity relations (PLRs) is very small (e.g. 0.138 mag in the F160W sample I PLR). We find no broken slope in the PLRs when analyzing our entire sample, but we do identify a subsample of Cepheids that causes the broken slope. However, this effect only shows when the number of this Cepheid type makes up a significant fraction of the total sample. We also analyze the sample selection effect on the Hubble constant.