Euclid: The rb-M∗ relation as a function of redshift. I. The 5 × 109M⊙ black hole in NGC 1272⋆

Core ellipticals are the results of dry mergers. During these events a binary black hole is formed, destroying the original cuspy central regions of the merging objects and scatters stars that are not on tangential orbits. The size of the emerging core correlates with the mass of the finally merged black hole. In this work we report the first Euclid-based mass determination of a supermassive black hole. We perform it by studying the center of NGC 1272, the second most luminous elliptical galaxy in the Perseus cluster, combining the Euclid VIS photometry coming from the Early Release Observations of the Perseus cluster with VIRUS spectroscopic observations at the Hobby-Eberly Telescope. The core of NGC 1272 is detected on the Euclid VIS image of the Perseus cluster. Its size is 1. ′′29 ± 0. ′′07 or 0.45 kpc, determined by fitting PSF-convolved core-Sérsic and Nuker-law functions. We deproject the surface brightness profile of the galaxy, finding that the galaxy is axisymmetric and nearly spherical. The two-dimensional stellar kinematics of the galaxy is measured from the VIRUS spectra by deriving optimally regularized non-parametric line-of-sight velocity distributions. Dynamical models of the galaxy are constructed using our axisymmetric and triaxial Schwarzschild codes. We measure a black hole mass of (5 ± 3) × 109M⊙, in line with the expectation from the MBH-rb correlation, but eight times larger than predicted by the MBH-σ correlation. The core size, rather than the velocity dispersion, allows one to select galaxies harboring the most massive black holes. The spatial resolution, wide area coverage, and depth of the Euclid (Wide and Deep) surveys allow us to find cores of passive galaxies larger than 2 kpc up to redshift 1.Key words. Galaxies: kinematics and dynamics; elliptical and lenticular, cD; individual: NGC 1272; nuclei; photometry