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G. A. Bower, R. F. Green (NOAO/KPNO), K. Gebhardt (UC-Santa Cruz), R. Bender (Universitäts-Sternwarte, München, Germany), STIS Team
The STIS Investigation Definition Team is conducting a long-term program to confirm the presence of dark compact objects (presumably supermassive black holes, hereafter BHs) in the nuclei of several galaxies based on preliminary evidence from earlier studies, and to search for evidence of BHs in a sample of galaxies where the ground-based dynamical evidence for a BH is non-existent or weak. Through this program, we will contribute to the effort toward understanding the demographics of BHs, which are interesting for two reasons. Firstly, present data indicate a possible relationship between the mass of a BH and the mass of the galaxy spheroid within which it is embedded, thus suggesting that BH formation may be closely linked to the formation of galaxy bulges. Secondly, the demographics of local BHs provide a constraint on the accretion properties of quasars at earlier cosmological epochs.
In this talk and others by our team in this session, we present preliminary results from our STIS spectroscopy of a selection of galaxies from our program. The primary observational diagnostic of a dark compact mass is measuring and interpreting the nuclear stellar dynamics in the sphere of influence of the candidate BH. The observations involve long-slit spectroscopy of a galaxy nucleus with the wavelength coverage including the strong Ca II triplet absorption lines near 8600~Å. After calibrating the spectrum, we measure the stellar dynamics using the Fourier Correlation Quotient method. These measurements map the nuclear gravitational potential. Using the observed stellar dynamics and surface brightness distribution as input, we fit galaxy dynamical models to these observations to determine if there is evidence for a dark compact object. This talk presents this methodology applied to NGC~1023, which was the first galaxy observed in our program.
Support for this work was provided to the STIS IDT by NASA.