Extreme Values of Black-hole-to-stellar-mass Ratio for High-redshift Galaxies

Abstract With recent data from the James Webb Space Telescope (JWST), it is possible to calculate the mass of the supermassive black holes at the center of galaxies and the stellar mass of the host galaxies at redshift z ≳ 5. In this work, we apply extreme-value statistics to calculate the distributions of extreme black-hole and stellar masses for galaxies in the redshift range 3 ≲ z ≲ 8. We show that under certain assumptions about the stellar and black-hole mass functions, a high ratio of M BH / M * ∼ 0.3−0.5 can be obtained without invoking additional black hole growth physics. Nevertheless, surveying a range of extreme-value methodologies, we find predictions of the extreme ratio M BH / M * to still be in slight tension with the high values observed by JWST.