12 October 2014
Congratulations to Ece Kilerci Ese
Ece Kilerci Ese successfully defended her PhD thesis "Active Galaxies: A Study of Local Seyferts and Ultra Luminous Infrared Galaxies" on Monday, 12 October 2014. Ece has been working at DARK with supervisor Marianne Vestergaard.
Abstract: Galaxy formation and evolution is one of the main research themes of modern astronomy. Active galaxies such as Active Galactic Nuclei (AGN) and Ultraluminous Infrared Galaxies (ULIRGs) are important evolutionary stages of galaxies. The ULIRG stage is mostly associ- ated with galaxy mergers and interactions. During the interactions of gas-rich galaxies, the gas inflows towards the centers of the galaxies and can trigger both star formation and AGN activity. The ULIRG stage includes rapid star formation activity and fast black hole growth that is enshrouded by dust. Once the AGN emission is sufficiently powerful, energy feedback from the AGN blows away the gas fuel and shuts off both the star formation and the black hole growth.
In this thesis I study local AGN and ULIRGs. I address 2 different studies of AGN: one is related to the potential use of AGN to measure cosmic distances and the other one is related to the mass estimates of supermassive black holes (SMBHs). Mass estimates of SMBHs are important to understand the formation and evolution of SMBHs and their host galaxies. Black hole masses in Type 1 AGN are measured with the reverberation mapping (RM) technique. Reverberation mapping analyses of ∼50 nearby AGN show a tight correlation between the broad line region (BLR) radius (R) and the mean optical luminosity (L) that is known as the R − L relationship. The R − L relationship traditionally is used to formulate the mass scaling relationships, which are used estimate BH masses based on a single-epoch spectrum.
Recently, it has been shown that the R − L relationship can also be used to measure cosmic distances beyond redshifts that can be probed by supernovae. The current local (z <∼ 0.3) RM AGN sample has a scatter of ∼0.33 mag in the distance modulus. This scatter is directly related to the observed scatter of 0.13 dex in the R − L relationship. In Chapter 2, I investigate the origin of the scatter in the R − L relationship. I find that usage of the UV luminosity can potentially reduce the observed scatter in the R − L relationship and thus the scatter in the AGN Hubble diagram which would help for our use of quasars as cosmic distance indicators.
The mass scaling relationships enables us to estimate BH masses of Type 1 AGN with an uncertainty of a factor of ∼4. An accurate line width characterization is important in order to minimize the uncertainty of the mass estimates based on the scaling relationships. In Chapter 3, I investigate the potential effect of the accretion luminosity on the line width characterization of the broad emission lines that are used in BH mass estimates. I use publicly available optical, UV and X-ray data to obtain quasi-simultaneous spectral energy distributions and directly measure the accretion luminosity. I find an inverse correlation between the Eddington luminosity ratio (accretion luminosity normalized by the BH mass) and the Hβ line shape.
In Chapter 4, I present a catalog of local ULIRGs identified in the AKARI All-sky Survey. I identify new ULIRGs and increase the number of known ULIRGs in the local Universe. I use infrared and optical imaging and spectroscopic data from AKARI and SDSS. I investigate mor- phologies, optical spectral types, star formation rates (SFR), stellar masses (M⋆), metallicities and, colors of the ULIRGs in my sample.
Read her thesis here >>