Abstract
Reverberation mapping is a robust method to measure the masses of supermassive black holes outside of the local Universe. Measurements of the radius鈥搇uminosity (R鈭扡) relation using the Mg鈥塱i emission line are critical for determining these masses near the peak of quasar activity at z 鈮� 1鈭�2, and for calibrating secondary mass estimators based on Mg鈥塱i that can be applied to large samples with only single-epoch spectroscopy. We present the first nine Mg鈥塱i lags from our 5-yr Australian Dark Energy Survey reverberation mapping programme, which substantially improves the number and quality of Mg鈥塱i lag measurements. As the Mg鈥塱i feature is somewhat blended with iron emission, we model and subtract both the continuum and iron contamination from the multiepoch spectra before analysing the Mg鈥塱i line. We also develop a new method of quantifying correlated spectroscopic calibration errors based on our numerous, contemporaneous observations of F-stars. The lag measurements for seven of our nine sources are consistent with both the H 尾 and Mg鈥塱i R鈭扡 relations reported by previous studies. Our simulations verify the lag reliability of our nine measurements, and we estimate that the median false positive rate of the lag measurements is 4 per cent鈦�.
