A First Look at Cepheids in a Type Ia Supernova Host with JWST

We report the first look at extragalactic Cepheid variables with James Webb Space Telescope, obtained from a serendipitous (to this purpose) observation of NGC 1365, host an SN Ia (SN 2012fr), calibration path used to measure Hubble constant. As expected, high-resolution observations NIRCam through F200W show better source separation line-of-sight companions than HST images similar near-infrared wavelengths, spectral region that has been mitigate impact dust on distance measurements. Using standard star P330E as zeropoint and PSF reference, we photometered 31 previously-known Cepheids in JWST field, spanning 1.15 < log P 1.75 including 24 longer period interval 1.35 1.75. compared resultant Period-Luminosity relations 49 full range 38 observed WFC3/IR transformed photometric system (F200W, Vega). The P-L measured two space telescopes are good agreement, intercepts (at P=1) 25.74+/-0.04 25.72+\-0.05 for JWST, respectively. Our baseline result comes where have higher signal-to-noise ratios find 25.75+\-0.05 25.75+\-0.06 mag consistency between measurement HST, no evidence photometry is "biased bright" ~0.2 level would be needed Tension, though comparisons more hosts warranted anticipated. expect future surpass these quality they will optimized measuring Cepheids.