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Paper: Intermediate-mass Black Hole Candidates in the Galactic Center
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 149
Authors: Takekawa, S.; Oka, T.; Iwata, Y.; Tsujimoto, S.; Nomura, M.
Abstract: Supermassive black holes (SMBHs) are hypothesized to grow through multiple merging and accretion of “seed” intermediate-mass black holes (IMBHs). The discovery of IMBHs is essential for understanding the origin of SMBHs and evolution of galaxies. However, the existence of IMBHs has still remained controversial. In the Galactic center, the infrared source IRS13E has been suggested to harbor an IMBH based on the stellar dynamics and the high-velocity feature of the ionized gas. High-velocity compact clouds (HVCCs), which are peculiar molecular clouds with small spatial sizes and extremely broad velocity widths, may also provide hints for the existence of IMBHs. Although still controversial, CO–0.40–0.22 is the first example of the HVCC suggested to harbor a massive IMBH. Recently, we have conducted the high-resolution molecular line observations of two HVCCs near the Galactic nucleus. In these observations, we have discovered gas streams showing clear orbital motions around invisible gravitational sources. The kinematical features and absences of other-wavelength counterparts suggest that the gravitational sources may probably be inactive massive IMBHs. Our results provide new circumstantial evidences for wandering IMBHs around the Galactic nucleus. We have successively found non-luminous IMBH candidates in the Galactic center. HVCCs may potentially be a key population to search for quiescent black holes lurking in the Galaxy.
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