Cepheid theoretical models and observations in HST/WFC3 filters: The effect on the Hubble constant H0

Abstract

We present a complete theoretical scenario for classical Cepheids in the most commonly used Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) filters, going from optical (F555W, F606W and F814W) to near-infrared (F160W) bands. The importance of such a study is related to the recent release of new classical Cepheids observed with HST/WFC3 in eight distant galaxies where supernovae Ia are hosted. These observations have posed sound constraints to the current distance scale with uncertainties on the Hubble constant H0 smaller than 3 per cent. Our models explore a large range of metallicity and Helium content, thus providing a robust and unique theoretical tool for describing these new and future HST/WFC3 observations. As expected, the Period-Luminosity (PL) relation in F160W filter is linear and slightly dependent on the metallicity when compared with optical bands, thus it seems the most accurate tool to constrain extragalactic distances with Cepheids. We compare the pulsation properties of Cepheids observed with HST/WFC3-IR with our theoretical scenario and we discuss the agreement with the predicted Instability Strip for all the investigated galaxy samples including the case of NGC 4258. Finally, adopting our theoretical F160W PL relation for Z = 0.02 and log P {greater than but not simslar to} 1.0, we derive new distance moduli. In particular, for NGC 4258, we derive a distance modulus μ0 = 29.345 ± 0.004 mag with a σ = 0.34 mag, which is in very good agreement with the geometrical maser value. Moreover, using the obtained distance moduli, we estimate the Hubble constant value, H0 = 76.0 ± 1.9 km s-1 Mpc-1 in excellent agreement with the most recent literature values. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.