Bonita De Swardt
Bonita De Swardt, PhD Student
Department of Astronomy ,
University of Cape Town,
Rondebosch, 7700,
South Africa
Phone: +27 21 650 2395
Email: bonita@mensa.ast.uct.ac.za
or bonitade@gmail.com
Research Interests
Local Volume Dwarf Galaxies, Detection of Intermediate-mass Black-Holes in dense Stellar Systems, Dark matter content in local dwarfs, Stellar populations in Galactic Globular Clusters and dwarf elliptical galaxies, chemical evolution of dwarf elliptical/lenticular galaxies, nuclear star clusters and black holes in dwarf galaxies
Current Research Projects
The detection of Intermediate-Mass Black Holes in Galactic Globular Clusters
This is a SALTICAM BVR-color image of Galactic globular cluster NGC 6864. One of my research projects involves the search of intermediate-mass black holes in the centers of Galactic globular clusters. We will do this by looking at the kinematical behaviour of stars near the cluster center where the gravitational effects of a possible black hole can be detected. This project involves using spectroscopic data obtained with SALT 's Robert Stobie Spectrograph (RSS).
Intermediate-Mass Black Holes in the centers of dwarf Elliptical Galaxies
The relationship between black hole mass and the central/bulge velocity dispersion is well established for early-type galaxies. It remains questionable whether this correlation can be extended to galaxies having lower central velocity dispersions. Dwarf galaxies would serve as ideal candidates to explore the lower end of the BH-mass vs. velocity dispersion relation. The enclosed region shows the range in central velocity dispersions expected for our sample of Local Volume dwarf elliptical galaxies. If the BH-mass vs. velocity dispersion relation can be extrapolated to this lower mass regime, it is likely that these dwarfs are possible hosts of the highly debatable "Intermediate-mass Black Hole" (IMBH). Currently, no secure IMBH detections have been made in dwarf galaxies. However, upper mass estimates to a possible IMBH have been measured for 6 Virgo cluster dwarf elliptical galaxies together with Andromeda's companian, NGC205.
This project involves acquiring SALT RSS long-slit spectra along the major-axis of dwarf galaxies in determining the velocity dispersion profile. This dispersion profile will give us the necessary clues to infer the possible existance of a BH within the galaxy center. Further constraints on the BH-mass can only be resolved through dynamical modeling of the galaxy.
Near-infrared JHKs Imaging of Local Volume dwarf galaxies
We have obtained JHKs observations of 6 Local Volume dwarf galaxies using the 1.4m IRSF telescope in Sutherland, South Africa. Exposure times range from 40min (for the brighter dwarfs) to 1h30min. Surface brightness profiles will be extracted for each galaxy in the sample. The surface brightness profiles together with the velocity dispersions measured from the optical spectra, will be used to obtain a dark matter estimate of the galaxy.
The reduced color images of our sample dwarf galaxies are shown below.
NGC 59 - A dwarf galaxy with a double nucleus?
The dwarf galaxy NGC 59 is situated on outskirts of the nearby Centaurus Group (D~3.6Mpc). This galaxy is classified as dwarf lenticular and shows star-formation activity near its center. The IRSF H-band image on the left zooms into the central region of NGC 59 revealing a double nuclear component. Four HII star-forming regions have been detected close to the galaxy center in Halpha. The locations of the peak in Halpha emission is shown by the blue points on the image. We have also obtained long-slit spectroscopic data for this galaxy in measuring its major-axis kinematics. The position of the slit is indicated on this image which should be centered on the galaxy center (shown by the black point).
The stellar and gas kinematics along the major-axis confirm that this galaxy is rotationally supported. Its maximum rotational velocity lies in the range of 20-30km/s which is a typical value for transition-type dwarf galaxies (eg. dwarf irregular galaxies). The nature of the double nuclear component is still being investigated. The spectra obtained with the SALT telescope together with the near-infrared imaging will provide more clues to the evolution of this intriguing dwarf galaxy.
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