Kavli Affiliate: Wendy L. Freedman
| First 5 Authors: Wendy L. Freedman, Barry F. Madore, , ,
| Summary:
Cepheids have been the cornerstone of the extragalactic distance scale for a
century. With high-quality data, these luminous supergiants exhibit a small
dispersion in their Leavitt (period-luminosity) relation, particularly at
longer wavelengths, and few methods rival the precision possible with Cepheid
distances. In these proceedings, we present an overview of major observational
programs pertaining to the Cepheid extragalactic distance scale, its progress
and remaining challenges. In addition, we present preliminary new results on
Cepheids from the James Webb Space Telescope (JWST). The launch of JWST has
opened a new chapter in the measurement of extragalactic distances and the
Hubble constant. JWST offers a resolution three times that of the Hubble Space
Telescope (HST) with nearly 10 times the sensitivity. It has been suggested
that the discrepancy in the value of the Hubble constant based on Cepheids
compared to that inferred from measurements of the cosmic microwave background
requires new and additional physics beyond the standard cosmological model.
JWST observations will be critical in reducing remaining systematics in the
Cepheid measurements and for confirming if new physics is indeed required.
Early JWST data for the galaxy, NGC 7250 show a decrease in scatter in the
Cepheid Leavitt law by a factor of two relative to existing HST data and
demonstrate that crowding/blending effects are a significant issue in a galaxy
as close as 20 Mpc.
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