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Astro lunch 19.06.2018

Le 19 juin 2018
De 12h45 à 13h45

Karina Voggel (Utah Uni.)

"The hunt for super-massive black holes in UCDs - Stripped nuclei as tracers of the assembly history of a Galaxy Cluster”


Central super-massive BHs (SMBHS) have been discovered in five high mass ultra-compact dwarfs (UCDs) that account for up to ~15% of their total mass. This essentially confirms that many high-mass UCDs are the remaining nuclei of stripped galaxies. The existence of SMBHs in UCDs could significantly increase the total number of known SMBHs in the local universe.

Having a measure of the total amount of stripped Nuclei in a Galaxy cluster would be a unique direct probe of its past merger history and yield an important census of this previously hidden population of SMBHs. Such a census of SMBHs in the local Universe are a crucial ingredient for models in which SMBHs grow through galaxy mergers. The low-frequency gravitational waves of such merging SMBH will be the prime targets for upcoming space-based gravitational wave detectors such as LISA.

Here I will present a new method that provides a way to estimate the SMBH occupation fraction of UCDs utilizing only their dynamical masses from integrated spectroscopy.  Our work on massive UCD found that inflated M/Ls do in fact indicate the presence of massive BHs in their centers. Based on this, we develop a new approach that uses the average elevation of UCDs mass-to-light ratios as a proxy to constrain the presence of SMBHs. This allows us for the first time to estimate the total amount and luminosity function of stripped nuclei and thus hidden SMBHs in a nearby Galaxy Cluster (e.g. Fornax and Virgo). Thus, UCDs with SMBHs can be used as a unique tool to directly study the past merger history of a galaxy cluster.

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