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Dieu Duc Nguyen Thesis Defense 05/02/2018

Thesis Defense

Dieu Duc Nguyen Wednesday, May 2, 2018 at 1:00 PM (110 INSCC)

Title: Low-Mass Nearby Early-Type Galaxies at High Resolution - Dynamical Measurement of Massive Black Hole Mass Nuclear Star Cluster Mass

The motions of stars or gas at the centers of every galaxy may provide evidence for the presence of a central supermassive black hole (BH). Although this picture is well established in massive galaxies, it is unclear in lower mass counterparts. Many works have proved that only a fraction of low-mass galaxies appears to host BHs and called the ``occupation fraction". The current model of BH seed formation mechanisms in the early Universe are very sensitive to the predicted occupation fraction of a BH in low-mass galaxies in the local universe, and closely reflect the origins of a galaxy and BH formation and (co)evolution throughout the cosmic history. My work of measuring the masses of putative BHs in a complete and unbias sample of nearby low-mass early-type galaxies using dynamical methods of stars and ionized gas as the first step to dynamical constraint the occupation fraction. Finding BHs in low-mass galaxies is challenging due to their small mass if they actually exist, and then their sphere of influence radii are smaller or only marginally resolved by the most current powerful telescope and the difficulty of separating their mass from the nuclear star cluster (NSC) mass. However, I was successful to measure the masses of two sub-million mass BHs in NGC 5102 and NGC 5206 using stellar dynamical method for the first time. My work also measures the mass of a few million solar masses BH in M32 and put firm upper limit constraints on two less than 100 thousands solar masses BHs in NGC 205 and NGC 404. These account for a large fraction (~50\%) of (sub)millions solar masses BHs that have masses have handful constrained so far. This extends to the low-mass regime of both BHs and host galaxies shows their BH mass--host properties scaling relations are largely offset from their massive cousins, suggesting a different feedback mechanism may occurs in low-mass. Additionally, with high-resolution imaging and spectroscopy and the proximity of the sample, I examine in detail their NSCs morphology, composition, and dynamical masses in detail to shed a light on their formation origin. Especially, I find a massive NSC in the nearby starburst galaxy Henize 2-10 is forming in progress due to the migration of massive star clusters towards the center where a pre-existing BH is present already.

Last Updated: 12/21/18