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The Environments Around Nearby Supermassive Black Holes and the Upgrade of the OSIRIS Integral Field Spectrograph

  • Author(s): Boehle, Anna Lee
  • Advisor(s): Larkin, James E
  • et al.
Abstract

In this thesis, I explore the environments around supermassive black holes (SMBHs) in the nearby universe. The thesis is divided into five chapters. I begin with an introduction to SMBHs in general and to the astronomical instrumentation that is used to study their direct environments in the highest possible detail. The second chapter focuses on the closest galactic nucleus to Earth: the center of our own Milky Way galaxy. The orbits of stars around the Milky Way SMBH, Sgr A*, can be used to determine the black hole mass and distance. I present a new method of analyzing images of the Galactic center to increase the time baseline for faint, short-period stars that orbit Sgr A*. I use this new analysis method to improve the constraints on the mass of the SMBH and the distance to the Galactic center by a factor of 2. The second chapter discusses the upgrade of the detector in the OSIRIS instrument at W.M. Keck Observatory. This adaptive-optics-fed instrument uses an array of small lenses to sample a rectangular section of the focal plane, producing up to 3,000 spectra simultaneously with a spectral resolution of 3,800 and diffraction-limited spatial resolution. I helped to upgrade the original near-infrared (NIR) Hawaii-2 detector to a Hawaii-2RG, which improved the raw sensitivity of OSIRIS by a factor of 2 at J-band wavelengths (1.2 - 1.4 μm) and 1.6 at H- and K-band wavelengths (1.5 - 2.4 microns). The third and fourth chapters discuss a NIR integral field spectroscopic survey of nearby LINER (low ionization nuclear emission line) galaxies, the lowest luminosity class of active galactic nuclei. LINERs are found at the centers of ∼1/3 of galaxies within 40 Mpc, but it is unclear whether accretion onto a supermassive black hole or another mechanism such as shock excitation drives their emission. I use the OSIRIS instrument to map the strength and kinematics of singly ionized iron, molecular hydrogen, and hydrogen recombination lines at spatial scales of 1-10 pc in the nuclei of 11 nearby LINERs, in close proximity to their central SMBHs. The third chapter presents a detailed study of the closest LINER in the sample, NGC 404, in which I find that its LINER emission is likely excited by shocks, and the final chapter presents results from the survey sample as a whole.

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