Poster Presentation
Investigating the Relationship between Outflows and Metallicity Using Emission-Line Ratios in BAL Quasars
Presenter: Nozomu Tamada (Ehime University)
The observed correlation between the masses of supermassive black holes (SMBHs) and their host galaxies suggests their co-evolution, yet the physical processes of this co-evolution remain poorly understood. Quasar outflows are thought to play a key role in quenching star formation, although the mechanisms that drive these outflows are still unclear. Previous studies have reported a correlation between the outflow intensity and the metallicity of the broad-line region (BLR) surrounding the SMBH (Wang et al. 2012). Emission-line or absorption-line profiles are often used to study the details of outflows. In particular, outflows can be observed as broad absorption lines when the gas crosses our line of sight, which serves as an additional diagnostic of outflow properties.
Motivated by this context, we examined the relationship between BLR emission-line flux ratio as a tracer of metallicity and the outflow strength inferred from BAL profiles. To quantify the strength of outflow, we performed the continuum fitting and calculated the BAL terminal velocities for 23,101 BAL quasars selected from the Sloan Digital Sky Survey DR16 quasar catalog (Lyke et al. 2020). Consequently, we carried out the spectral fitting for composite spectra grouped by these BAL terminal velocities and derived the BLR emission-line flux ratios. As a result, we identify a clear positive correlation between BLR emission-line flux ratios and BAL terminal velocities, implying a possible connection between metallicity and outflow strength.
In this poster, we present the details of our analysis and the interpretation of the resulting positive correlation.
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