Upper Limits on the Presence of Central Massive Black Holes in Two Ultra-compact Dwarf Galaxies in Centaurus A

The recent discovery of massive black holes (BHs) in the centers of high-mass ultra-compact dwarf galaxies (UCDs) suggests that at least some are the stripped nuclear star clusters of dwarf galaxies. We present the first study that investigates whether such massive BHs, and therefore stripped nuclei...

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Published in:The Astrophysical journal 2018-05, Vol.858 (1), p.20
Main Authors: Voggel, Karina T., Seth, Anil C., Neumayer, Nadine, Mieske, Steffen, Chilingarian, Igor, Ahn, Christopher, Baumgardt, Holger, Hilker, Michael, Nguyen, Dieu D., Romanowsky, Aaron J., Walsh, Jonelle L., Brok, Mark den, Strader, Jay
Format: Article
Language:English
Subjects:
Adaptive optics
Astronomical models
Astrophysics
Black holes
Compact galaxies
Dwarf galaxies
galaxies: dwarf
galaxies: kinematics and dynamics
galaxies: nuclei
galaxies: star clusters: general
Globular clusters
Nuclei
Optics
Star clusters
Stars & galaxies
Stellar kinematics
Stellar models
Very Large Telescope
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Summary:The recent discovery of massive black holes (BHs) in the centers of high-mass ultra-compact dwarf galaxies (UCDs) suggests that at least some are the stripped nuclear star clusters of dwarf galaxies. We present the first study that investigates whether such massive BHs, and therefore stripped nuclei, also exist in low-mass (M < 107 M ) UCDs. We constrain the BH masses of two UCDs located in Centaurus A (UCD 320 and UCD 330) using Jeans modeling of the resolved stellar kinematics from adaptive optics data obtained with the SINFONI integral field spectrograph at the Very Large Telescope (VLT/SINFONI). No massive BHs are found in either UCD. We find a 3 upper limit on the central BH mass in UCD 330 of M < 1.0 × 105 M , which corresponds to 1.7% of the total mass. This excludes a high-mass fraction BH and would only allow low-mass BHs similar to those claimed to be detected in Local Group globular clusters. For UCD 320, poorer data quality results in a less constraining 3 upper limit of M < 1 × 106 M , which is equal to 37.7% of the total mass. The dynamical mass-to-light ratios of UCD 320 and UCD 330 are not inflated compared to predictions from stellar population models. The non-detection of BHs in these low-mass UCDs is consistent with the idea that elevated dynamical mass-to-light ratios do indicate the presence of a substantial BH. Although no massive BHs are detected, these systems could still be stripped nuclei. The strong rotation (v/ of 0.3-0.4) in both UCDs and the two-component light profile in UCD 330 support the idea that these UCDs may be stripped nuclei of low-mass galaxies whose BH occupation fraction is not yet known.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aabae5