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Abstract The Dark Energy Spectroscopic Instrument (DESI) collaboration measured a tight relation between the Hubble constant (H₀) and the distance to the Coma cluster using the fundamental plane (FP) relation of the deepest, most homogeneous sample of early-type galaxies. To determineH₀, 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 13 Type Ia supernovae (SNe Ia) in the cluster with a mean standardized brightness of $m_B^0=15.710\pm 0.040$mag. Calibrating the absolute magnitude of SNe Ia with the Hubble Space Telescope (HST) distance ladder yieldsD_Coma = 98.5 ± 2.2 Mpc, consistent with its canonical value of 95–100 Mpc. This distance results inH₀ = 76.5 ± 2.2 km s⁻¹Mpc⁻¹from the DESI FP relation. Inverting the DESI relation by calibrating it instead to the Planck+ΛCDM value ofH₀ = 67.4 km s⁻¹Mpc⁻¹implies a much greater distance to Coma,D_Coma = 111.8 ± 1.8 Mpc, 4.6σbeyond a joint, direct measure. Independent of SNe Ia, the HST Key Project FP relation as calibrated by Cepheids, the tip of the red giant branch from JWST, or HST near-infrared surface brightness fluctuations all yieldD_Coma < 100 Mpc, in joint tension themselves with the Planck-calibrated route at >3σ. 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+ΛCDM 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. 

Abstract We present optical follow-up imaging obtained with the Katzman Automatic Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo gravitational wave (GW) signal from the neutron star–black hole (NSBH) merger GW190814. We searched the GW190814 localization region (19 deg 2 for the 90th percentile best localization), covering a total of 51 deg 2 and 94.6% of the two-dimensional localization region. Analyzing the properties of 189 transients that we consider as candidate counterparts to the NSBH merger, including their localizations, discovery times from merger, optical spectra, likely host galaxy redshifts, and photometric evolution, we conclude that none of these objects are likely to be associated with GW190814. Based on this finding, we consider the likely optical properties of an electromagnetic counterpart to GW190814, including possible kilonovae and short gamma-ray burst afterglows. Using the joint limits from our follow-up imaging, we conclude that a counterpart with an r -band decline rate of 0.68 mag day −1 , similar to the kilonova AT 2017gfo, could peak at an absolute magnitude of at most −17.8 mag (50% confidence). Our data are not constraining for “red” kilonovae and rule out “blue” kilonovae with M > 0.5 M ⊙ (30% confidence). We strongly rule out all known types of short gamma-ray burst afterglows with viewing angles <17° assuming an initial jet opening angle of ∼5.°2 and explosion energies and circumburst densities similar to afterglows explored in the literature. Finally, we explore the possibility that GW190814 merged in the disk of an active galactic nucleus, of which we find four in the localization region, but we do not find any candidate counterparts among these sources.