Abstract
Abstract We present an improved determination of the Hubble constant from Hubble Space Telescope (HST) observations of 70 long-period Cepheids in the Large Magellanic Cloud (LMC). These were obtained with the same WFC3 photometric system used to measure extragalactic Cepheids in the hosts of SNe Ia. Gyroscopic control of HST was employed to reduce overheads while collecting a large sample of widely separated Cepheids. The Cepheid period–luminosity relation provides a zero-point-independent link with 0.4% precision between the new 1.2% geometric distance to the LMC from detached eclipsing binaries (DEBs) measured by Pietrzyński et al. and the luminosity of SNe Ia. Measurements and analysis of the LMC Cepheids were completed prior to knowledge of the new DEB LMC distance. Combined with a refined calibration of the count-rate linearity of WFC3-IR with 0.1% precision, these three improved elements together reduce the overall uncertainty in the geometric calibration of the Cepheid distance ladder based on the LMC from 2.5% to 1.3%. Using only the LMC DEBs to calibrate the ladder, we find H 0 = 74.22 ± 1.82 km s−1 Mpc−1 including systematic uncertainties, 3% higher than before for this particular anchor. Combining the LMC DEBs, masers in NGC 4258, and Milky Way parallaxes yields our best estimate: H 0 = 74.03 ± 1.42 km s−1 Mpc−1, including systematics, an uncertainty of 1.91%–15% lower than our best previous result. Removing any one of these anchors changes H 0 by less than 0.7%. The difference between H 0 measured locally and the value inferred from Planck CMB and ΛCDM is 6.6 ± 1.5 km s−1 Mpc−1 or 4.4σ (P = 99.999% for Gaussian errors) in significance, raising the discrepancy beyond a plausible level of chance. We summarize independent tests showing that this discrepancy is not attributable to an error in any one source or measurement, increasing the odds that it results from a cosmological feature beyond ΛCDM.
Highlights
Cepheid variables in the Magellanic Clouds (Leavitt & Pickering 1912; Hertzsprung 1913) have long played a starring role in the distance scale and the determination of the present value of the expansion rate of the Universe, the Hubble constant (H0)
We present an improved determination of the Hubble constant from Hubble Space Telescope (HST) observations of 70 long-period Cepheids in the Large Magellanic Cloud
The 70 Large Magellanic Cloud (LMC) Cepheids presented here were imaged in three bands, two in the optical with WFC3UVIS (F 555W and F 814W ) and one in the near-infrared with WFC3-IR (F 160W ), in two HST programs: GO-14648 and GO-15146 (PI: Riess)
Summary
Cepheid variables in the Magellanic Clouds (Leavitt & Pickering 1912; Hertzsprung 1913) have long played a starring role in the distance scale and the determination of the present value of the expansion rate of the Universe, the Hubble constant (H0). The resulting ability to determine distances to SNe Ia deep into the Hubble-Lemaıtre flow completes a distance ladder that provides the most precise, model-independent and direct means for determining H0 Knowledge of this cosmological parameter remains central to describing the present state of our Universe and setting expectations for its fate. Using a newly available commanding and control sequence under purely gyroscopic-control called “DASH” (Drift And SHift; Momcheva et al 2017) we observed up to a dozen LMC Cepheids in 3 filters in a single orbit, obtaining HST photometry for 70 widely-separated LMC Cepheids with WFC3 in 3 filters Only the final determination of H0 was completed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
