Testing AGN outflow and accretion models with C iv and He ii emission line demographics in z approximate to 2 quasars

Using approximate to 190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z approximate to 2 quasars. Specifically, we quantify how the shape of C iv lambda 1549 and the equivalent width (EW) of He ii lambda 1640 depend on the black hole mass and Eddington ratio inferred from Mg ii lambda 2800. Above L/L-Edd greater than or similar to 0.2, there is a strong mass dependence in both C iv blueshift and He ii EW. Large C iv blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He ii and 2 keV strength are broadly consistent with theoretical qsosed models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z approximate to 2 may in general have low spins. We find a dramatic switch in behaviour at L/L-Edd less than or similar to 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with qsosed predictions, hinting at changes in the structure of the broad line region. Overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.