MSc defense by Troels Paarup – University of Copenhagen

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MSc defense by Troels Paarup

Title: Quasar K-correction in the UV-optical spectral region and broad emission line shape parameter dependence on Eddington ratio


Context: Supermassive black holes are thought to reside in the center of both active- and quiescent galaxies. In the local universe, a remarkable relationship between these black hole masses and their host galaxy properties has been found, indicating a link between the evolution of the black holes and their host galaxies. Using this apparent evolutionary relationship between black holes and their host, by tracing the growth of the central black hole, might therefore be a way of probing galaxy evolution. This requires, however, reliable methods for measuring the black hole masses in the near and distant universe. The black hole mass in an AGN can be estimated by measuring a monochromatic continuum luminosity and broad emission line width in a single-epoch spectrum of the AGN. A comprehensive understanding of the broad emission line profiles is therefore a key to accurate and precise black hole mass estimation.

Method: This thesis consists of two parts: Part 1) Determining the optimal approach of estimating the K-correction in the SDSS u, g, r and i pass bands. This correction term needs to be added when shifting an observed photometric magnitude to rest and depends on the spectral energy distribution of the object. Since the AGN continuum emission in the UV-optical spectral region can be approximated by a single power law, I investigate how precise and accurate the AGN power law continuum can be estimated in SDSS spectra by two different methods: a) A fitting window method and b) a spectral decomposition method. I test the two methods by measuring the continuum emission in model artificial spectra – constructed with a large range of S/N, redshift and model power law continuum slopes. Furthermore, I investigate the emission line K-correction as function of z by a Monte Carlo approach. Part 2) Characterizing the AGN emission line shape by the FWHM / line dispersion ratio, I investigate whether the H! or C IV shape parameter depends on the ionizing luminosity based Eddington ratio. I use a known sample of AGNs to construct spectral energy distribution from which I measure the ionizing luminosities directly. The line widths used to estimate the shape parameter and Eddington ratio I estimate using the AGN single-epoch spectra.

Results 1) I find that the optimal way of estimating the K-correction is to use the fitting window method. In addition, I estimate the emission line K-correction as function of z in the SDSS u, g, r and i pass bands. Based on my results I quantify and tabulate the uncertainty in the K-correction for 4 different situations – depending on the purpose and amount of information available. 2) I do not find any correlation between H! shape parameter and Eddington ratio. Although I find a statistically significant correlation between C IV shape parameter and Eddington ratio, a partial correlation analysis has proven that the correlation is due to that the line width enters in both the dependentand independent variable. It therefore remains inconclusive from this study whether H! or C IV shape parameter depends on Eddington ratio. 

Friday, September 13
Time: 10:15
Place: DARK Lounge