Simulating supermassive black hole mass measurements for a sample of ultra massive galaxies using ELT/HARMONI high spatial resolution integral-field stellar kinematics

As the earliest relics of star formation episodes of the Universe, the most massive galaxies are the key to our understanding of the stellar population, cosmic structure, and SMBH evolution. However, the details of their formation histories remain uncertain. We address these problems by planning a large survey sample of 101 ultramassive galaxies ($z\le0.3$, $|\delta+24^{\circ}|<45$\deg, $|b|>8$\deg), including 76\% ellipticals, 17\% lenticulars, and 7\% spirals brighter than $M_K\le-27$~mag (stellar mass $2\times10^{12}\lesssim M_\star\lesssim5\times10^{12}$~\Msun) with ELT/HARMONI. Our sample comprises diverse galaxy environments ranging from isolated to dense-cluster galaxies. The primary goals of the project are to (1) explore the stellar dynamics inside galaxy nuclei and weigh SMBHs, (2) constrain the black hole scaling relations at the highest mass, and (3) probe the late-time assembly of these most massive galaxies through the stellar population and kinematical gradients. We describe the survey, discuss the distinct demographics and environmental properties of the sample, and simulate their HARMONI $I_z$, $I_z+J$, and $H+K$-band observations via combining the inferred stellar-mass models from Pan-STARRS observations, an assumed synthetic spectrum of stars, and SMBHs with masses estimated based on different black hole scaling relations. Our simulations produce excellent state-of-art IFS and stellar kinematics ($\Delta V_{\rm rms}\lesssim1.5$\%) in a relatively short exposure time. We use these stellar kinematics in combination with the JAM to reconstruct the SMBH mass and its error using the MCMC simulation. Thus, these simulations and modelings can be benchmarks to evaluate the instrument models and pipelines dedicated to HARMONI to exploit the unprecedented capabilities of ELT.