EXPLORING THE UNUSUALLY HIGH BLACK-HOLE-TO-BULGE MASS RATIOS IN NGC 4342 AND NGC 4291: THE ASYNCHRONOUS GROWTH OF BULGES AND BLACK HOLES

摘要: ABSTRACTWe study two nearby early-type galaxies, NGC 4342 and 4291, that host unusually massive black holesrelative to their low stellar mass. The observed black-hole-to-bulge mass ratios of 4291are 6 . 9 +3 8−2 3 % 1 9% ±0 6%, respectively, which significantly exceed the typical ratio ∼0 2%. Asa consequence exceedingly large ratios, 4291 are ≈5 σ ≈3 4 outliers from M • – bulge scaling relation, respectively. In this paper, we explore origin theunusually high ratio. Based on Chandra X-ray observations hot gas content ofNGC compute gravitating profiles, conclude both galaxies reside in massivedark matter halos, extend well beyond light. presence dark halos around 4342and a deep optical image environment indicate tidal stripping, 90% was lost, cannot explain ratios. Therefore,we these formed with masses, implying hole did notgrow tandem. We also find correlates properties halo,suggesting may play major role regulating growth supermassive holes.