Measuring Hubble’s Constant with JWST Observations of a Galaxy Clusters

Speaker: Brenda Frye

Date: Thursday, March 7, 2024

Time: 1:30 – 2:30 pm

Location: 472 Willamette Hall

Abstract: Galaxy clusters acting as gravitational lenses offer two advantages: to boost the brightnesses of objects in the background, and to map out the dark matter in the lens. With high resolution near-infrared observations introduced by the James Webb Space Telescope (JWST), a third advantage opens up to measure the Hubble’s constant. A review of cluster lensing in the first 18 months of JWST observations is presented, ranging from the spectacle of the publicly-available “first light” images to the galaxy cluster fields that uncover unprecedented levels of lensing evidence in the form of giant arcs and image multiplicities. A point-source was discovered in the JWST image of the galaxy cluster field PLCK G165.7+67.0 (G165) that is bright and appears in three different locations as a result of the lensing effect. Additional JWST observations confirm this source to be a normal Type Ia supernova (SN) at a redshift of 1.783 that we call “SN H0pe,” making it the highest redshift lensed standard candle. In a blinded approach, time delays between the images were measured, and six independent lens models were constructed. During the unblinding event, the time delays were converted into a value for Hubble’s constant by a scaled fit to the lens models. This is only the second measurement of Hubble’s constant by the method of a multiply-imaged supernova, and the first by the JWST. With JWST and other observatories coming on-line, this approach has a promising future.

Host: Graham Kribs