James Webb Space Telescope Feed Post

Harvard ADS: The Hubble Tension in our own Backyard: DESI and the Nearness of the Coma Cluster

Paper abstract: The Dark Energy Spectroscopic Instrument (DESI) collaboration measured a tight relation between the Hubble constant (H_0) and the distance to the Coma cluster using the fundamental plane (FP) relation of the deepest, most homogeneous sample of early-type galaxies. To determine H_0, we measure the distance to Coma by several independent routes each with its own geometric reference. We measure the most precise distance to Coma from 12 Type Ia Supernovae (SNe Ia) in the cluster with mean standardized brightness of m_B^0=15.712\pm0.041 mag. Calibrating the absolute magnitude of SNe Ia with the HST distance ladder yields D_{\textrm Coma}=98.5\pm2.2 Mpc, consistent with its canonical value of 95--100 Mpc. This distance results in H_0=76.5 \pm 2.2 km/s/Mpc from the DESI FP relation. Inverting the DESI relation by calibrating it instead to the Planck+\LambdaCDM value of H_0=67.4 km/s/Mpc implies a much greater distance to Coma, D_{\textrm Coma}=111.8\pm1.8 Mpc, 4.6\sigma beyond a joint, direct measure. Independent of SNe Ia, the HST Key Project FP relation as calibrated by Cepheids, Tip of the Red Giant Branch from JWST, or HST NIR surface brightness fluctuations all yield D_{\textrm Coma}< 100 Mpc, in joint tension themselves with the Planck-calibrated route at >3\sigma. From a broad array of distance estimates compiled back to 1990, it is hard to see how Coma could be located as far as the Planck+\LambdaCDM expectation of >110 Mpc. By extending the Hubble diagram to Coma, a well-studied location in our own backyard whose distance was in good accord well before the Hubble Tension, DESI indicates a more pervasive conflict between our knowledge of local distances and cosmological expectations. We expect future programs to refine the distance to Coma and nearer clusters to help illuminate this new, local window on the Hubble Tension.