Journal
ASTROPHYSICAL JOURNAL
Volume 753, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/753/2/140
Keywords
galaxies: bulges; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: individual (NGC 4291, NGC 4342); X-rays: galaxies; X-rays: ISM
Categories
Funding
- National Aeronautics and Space Administration [NAS8-03060]
- National Science Foundation [AST-0607526, AST-0707793, AST-1108964]
- NASA through Chandra X-ray Center [PF1-120081]
- Smithsonian Institution
- National basic research program of China (973 program) [2009CB24901]
- CAS
- NSFC [11143005]
- Max Planck Society
- Austrian Science Fund (FWF) [P 23946] Funding Source: researchfish
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We study two nearby early-type galaxies, NGC 4342 and NGC 4291, that host unusually massive black holes relative to their low stellar mass. The observed black-hole-to-bulge mass ratios of NGC 4342 and NGC 4291 are 6.9(-2.3)(+3.8)% and 1.9% +/- 0.6%, respectively, which significantly exceed the typical observed ratio of similar to 0.2%. As a consequence of the exceedingly large black-hole-to-bulge mass ratios, NGC 4342 and NGC 4291 are approximate to 5.1 sigma and approximate to 3.4 sigma outliers from the M-center dot-M-bulge scaling relation, respectively. In this paper, we explore the origin of the unusually high black-hole-to-bulge mass ratio. Based on Chandra X-ray observations of the hot gas content of NGC 4342 and NGC 4291, we compute gravitating mass profiles, and conclude that both galaxies reside in massive dark matter halos, which extend well beyond the stellar light. The presence of dark matter halos around NGC 4342 and NGC 4291 and a deep optical image of the environment of NGC 4342 indicate that tidal stripping, in which greater than or similar to 90% of the stellar mass was lost, cannot explain the observed high black-hole-to-bulge mass ratios. Therefore, we conclude that these galaxies formed with low stellar masses, implying that the bulge and black hole did not grow in tandem. We also find that the black hole mass correlates well with the properties of the dark matter halo, suggesting that dark matter halos may play a major role in regulating the growth of the supermassive black holes.
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