BS in Physics
Vardha N. Bennert
High-quality Keck/LRIS long-slit spectra for a sample of 97 active galaxies selected from the Sloan Digital Sky Survey (redshift between 0.02 & 0.1; Black Hole Mass approximately 107 Solar Masses) were obtained between January 2009 and March 2010 in order to study the black hole (BH) mass scaling relation in the local universe. Typically, the width of the broad Hβ emission line is used to measure the mass of the black hole (MBH). However, signs of variability in the emission line profile are seen for eight objects: While broad Hβ emission lines had previously been observed in spectra from the Sloan Digital Sky Survey (SDSS), they are missing in the Keck spectra. Based on seeing and PSF profile arguments, we can exclude that the lack of broad lines in the Keck spectra are caused by the telescope being pointed off center, missing the active nucleus. Follow-up observations were conducted in January and March 2013 in both Hβ, as well as Hα (which had not been obtained at Keck) using the Kast spectrograph mounted on the Shane three meter telescope at Lick observatory. Since SDSS uses a 3 arcsec fiber, the position angle of these long-slit observations was set perpendicular to the angle of the Keck longslit observations in order to search for any off-center broad emission. The broad emission lines remain missing in Hβ and are missing or reduced in Hα, suggesting changes in Seyfert classification transitions on timescales of approximately a decade. Observational constraints make variability of the torus or broad-line region over time as the most likely cause for this variation. However, at least in some cases, the existence of an AGN that is non-coincident with the center of the host galaxy due to an ongoing merger or gravitational recoil cannot be ruled out. The most promising candidate for such a scenario is SDSS J10383+4658 which shows a blue knot just off-center from the host galaxy, and could have been missed in Keck observations but is included in the SDSS fiber.