The Carnegie Hubble Program: The Infrared Leavitt Law in IC 1613

TL;DR

This study uses multi-wavelength infrared observations of Cepheids in IC 1613 to refine its distance and reddening, demonstrating that metallicity does not affect Cepheid distances at 3.6 microns, aiding precise Hubble constant measurements.

Contribution

First multi-band infrared Cepheid analysis of IC 1613 establishing reddening and distance, confirming metallicity independence at 3.6 microns.

Findings

Reddening E(B-V) = 0.05 mag

Distance modulus mu_0 = 24.29 mag

Metallicity has no measurable effect at 3.6 microns

Abstract

We have observed the dwarf galaxy IC 1613, at multiple epochs in the mid--infrared using Spitzer and contemporaneously in the near--infrared using the new FourStar near-IR camera on Magellan. We have constructed Cepheid period--luminosity relations in the J, H, K_s, [3.6] and [4.5] bands and have used the run of their apparent distance moduli as a function of wavelength to derive the line--of--sight reddening and distance to IC1613. Using a nine--band fit, we find E(B-V) = 0.05 +- 0.01 mag and an extinction--corrected distance modulus of mu_{0} = 24.29 +- 0.03_{statistical} +- 0.03_{systematic} mag. By comparing our multi--band and [3.6] distance moduli to results from the tip of the red giant branch and red clump distance indicators, we find that metallicity has no measurable effect on Cepheid distances at 3.6 microns in the metallicity range -1.0 < [Fe/H] < 0.2, hence derivations of the Hubble constant at this wavelength require no correction for metallicity.