MSc defense by Anna-Sofie Köhn Zahl – University of Copenhagen

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Dark Cosmology Centre > Calendar DARK > DARK Calendar 2015 > MSc defense by Anna-So...

MSc defense by Anna-Sofie Köhn Zahl

Title: Investigating the FeII/MgII-ratio as a possible metallicity tracer in high redshift Quasar

Supervisors: Marianne Vestergaard

Abstract:
The FeII/MgII-ratio have been suggested as a cosmic clock thereby it have implicitly been assumed that the ratio of UV FeII, which is measured in the range from 2000-30000 Å and MgII 2800 Å to be a tracer of the metallicity in quasars. The focus of this thesis is to determine whether the FeII-ratio scale with the metallicity in MgII quasars. The motivation for this investigation is that the FeII/MgII-ratio has been used as a tracer for the metallicity without compelling evidence of the existence of the relation. Therefore I examine 100 high redshift (3.5 ≤ z ≤ 4.5) quasar spectra from the XQ-100 Legacy Survey. For 95 of these quasars I could determine the metallicity based on line ratios of the broad emission lines and for 86 objects the FeII/MgII-ratio was available. In order to determine the metallicity I have used the scaling relation between specific broad emission line ratios and the metallicity (Hamann et al. 2002).

I show that the FeII/MgII-ratio is not correlated with the metallicity. This result apply to all QSOs and is statistical significant. The most likely reason why no scaling relation is present is because the FeII pseudo-continuum emission is more affected by other parameters of the gas than the abundance of Fe e.g. the microturbulence.

I also show that there is a relation between the mass and the luminosity and metallicity respectively. I further investigate if the activity, which is quantized as Lbol/Ledd, of the Quasars have a relation with the mass and the metallicity which I find that they have. This suggest co-evolution between QSOs and their host galaxies.

Read the thesis here>>