The Metallicity Dependence of the Cepheid P-L Relation in M101

Abstract

The impact of metallicity on the Cepheid Period-Luminosity (P-L) relation is investigated using HST ACS V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by -0.33 +/- 0.12 mag/dex and -0.71 +/- 0.17 mag/dex using 2 and 3 sigma rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2-sigma criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance modulus of 28.96 +/- 0.11 for M101 is obtained from 619 Cepheids, a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program).

17 pages, 17 figures, 2 tables, in press with the Astrophysical Journal

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• The effect of metallicity on Cepheid Period-Luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds
• The Carnegie-Chicago Hubble Program. VII. The Distance to M101 via the Optical Tip of the Red Giant Branch Method
• The Mira Distance to M101 and a 4% Measurement of H0
• Spitzer observations of SN 2014J and properties of mid-IR emission in Type Ia supernovae
• The Carnegie-Chicago Hubble Program. V. The Distances to NGC 1448 and NGC 1316 via the Tip of the Red Giant Branch
• The M31 Near-Infrared Period-Luminosity Relation and its non-linearity for $\delta$ Cep Variables with $0.5\le \log (P)\le 1.7$
• The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope
• The Extinction Properties of and Distance to the Highly Reddened Type Ia Supernova SN 2012cu
• Evidence for Photometric Contamination in Key Observations of Cepheids in the Benchmark Galaxy IC 1613