IRAC Band Period‐Luminosity Relations from LMC Cepheids: Application to Three Nearby Galaxies

It is well‐known in the cosmology community that an accurate determination of the Hubble constant $(H0),$ to within few percent, can be used to break the degeneracy between $ΩM$ and w in CMB measurements. The current uncertainty in $H0$ from the HST Key Project is about 10%. In contrast future observations by the James Webb Space Telescope (JWST) have the potential to deliver an $H0$ measurement accurate to under a few percent. This is because JWST will operate in the near‐ and mid‐infrared, thus significantly reducing the influence of extinction. Motivated by this, we derive Spitzer IRAC band period‐luminosity (PL) relations (the Leavitt Law) from the Large Magellanic Cloud Cepheids which can be applied to future distance scale measurements with JWST. To test these PL relations, we applied the IRAC band PL relations to the three nearby galaxies (NGC 6822, IC 1613 & WLM), where the Cepheid data were found from the Spitzer Archival data, and derive the distance moduli (in IRAC bands) to these galaxies. We also compare our results to the distance moduli derived using the reddening‐free Wesenheit function in optical.