BS in Physics
Vardha N. Bennert
The [OIII]/Hβnarrow ratio is a good first indicator of the source of ionization of gas in the vicinity of Active Galactic Nuclei (AGNs). If [OIII]/Hβnarrow > 10 then it is likely AGN ionization, for [OIII]/Hβnarrow < 3 it is likely attributed to star formation. While we know that all galaxies host an AGN, and thus expect at least the gas in the very central region to be AGN ionized, this research specifically focuses on the spatially resolved spectra at different distances from the center. We make use of an IDL code to fit the different components in high signal-to-noise optical long-slit spectra from the 10m Keck telescope of 87 Seyfert galaxies in the local universe (0.02 107M⊙) A transition of the gas from being predominantly AGN-ionized to ionization by stars in the galaxy allows us to determine the size of the Narrow Line Region (NLR). Of the 102 objects in our sample, when looking at the peak height [OIII]/Hβnarrow ratio, only 6 objects showed a clear transition between [OIII]/Hβnarrow > 10 to [OIII]/Hβnarrow < 3. There were 22 other objects that showed a basic transition (went from [OIII]/Hβnarrow > 3 to [OIII]/Hβnarrow < 3). These are still significant because we know that these objects are AGN ionized in the center so the size of their NLR is still determined. When looking at the integrated [OIII]/Hβnarrow ratio, 8 objects showed a clear transition, and 35 more showed a basic transition. 5 objects had an [OIII]/Hβnarrow < 3 throughout all of their spectra in both the integrated and peak height graphs which questions the use of BPT diagrams for determining ionization source.