M31 PAndromeda Cepheid Sample Observed in Four HST Bands

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.

A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES Team

“…In R16 we included measurements for 375 PHAT Cepheids before the availability of those from Li et al (2021). An expanded compilation from Kodric et al (2018) includes 522 Cepheids from the PHAT program with 3 < P < 78 days. We use the latter sample as an alternative to Li et al (2021) in some variants of our baseline analysis in Section 6.5 because of its powerful leverage to examine evidence of a possible break in the P-L relation near P ≈ 10 days.…”

“…Fits 27 and 28 exchange the Li et al (2021) sample of M31 Cepheids for the PHAT sample from Kodric et al (2018) with a 10 fold increase in the number of variables, but with filters that are transformed to the set of three used elsewhere rather than directly observed with them. The main value of this change is to gain further traction of a possible break at P = 10 days as discussed in the prior section.…”

A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team

“…Fits 27 and 28 exchange the Li et al (2021) sample of M31 Cepheids for the PHAT sample from Kodric et al (2018) with a ten-fold increase in the number of variables, but with filters that are transformed to the set of three used elsewhere rather than directly observed with them. The main value of this change is to gain further traction of a possible break at P = 10 d as discussed in the prior section.…”

A sub-2% Distance to M31 from Photometrically Homogeneous Near-Infrared Cepheid Period-Luminosity Relations Measured with the Hubble Space Telescope

“…Kodric et al (2018b) find a broken slope for M31 Cepheids in r, i, g, and Wesenheit bands. However, Riess et al (2016) did not find a broken slope in their m W H relation and Kodric et al (2018a) did not find a broken PLR slope in any of their samples using 522 fundamental mode Cepheids and 102 first overtone Cepheids in F 160W and F 110W as well as 559 fundamental mode Cepheids and 111 first overtone Cepheids in F 814W and F 475W , which is the largest Cepheid sample set compiled to date. To investigate the effect of Cepheids with P < 10 days on our distance determination, we removed Cepheids GRP-11.25609+41.56927 (PAndromeda ID: 1068323, Period = 6.85 days), GRP-11.03915+41.30692 (PAndromeda ID: 104540, Period = 9.362 days), GRP-11.20822+41.44917 (PAndromeda ID: 237868, Period = 4.133 days) and GRP-11.24332+41.50926 (PAndromeda ID: 1052211, Period = 5.751 days) from the gold+silver sample.…”

“…Blending has been shown to bias ground-based observations by up to 0.2 mag (Mochejska et al 2000;Vilardell et al 2007), and both crowding and differential extinction cause high dispersion in the Cepheid PLR. While past studies (Macri et al 2001;Riess et al 2012;Wagner-Kaiser et al 2015;Kodric et al 2018a) have shown that space-borne observations can help reduce the effects of crowding and blending, inhomogeneities between the filter systems used to observe Cepheids in M31 and their geometric calibrations yielded uncertainties in the distance measurements between 3% and 5%, limiting our knowledge of the distance to M31 and studies which use M31 to calibrate stellar luminosities.…”