Metallicity and Quasar Outflows

TL;DR

This study reveals a strong correlation between quasar outflow strength and metallicity, suggesting that higher metallicity enhances outflow acceleration, impacting galaxy evolution through feedback and enrichment.

Contribution

It is the first to demonstrate a direct, wide-range correlation between quasar metallicity and outflow strength using composite spectra from SDSS data.

Findings

Most ion line ratios increase with outflow strength.

CIV line strength decreases as metallicity increases.

Metallicity correlates strongly with outflow strength across a broad range.

Abstract

Correlations are investigated of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the CIV line (Wang et al. 2011), with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey. We find that most of the line ratios of other ions to CIV prominently increases with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of dominant coolant, CIV line, decreases and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using SiIV+OIV]/CIV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicitiy and the outflow strength of quasars over a wide range of 1.7 to 6.9 times solar abundance. Our result implies that the metallicity plays an important role in the formation of quasar outflows, likely via affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.