SDSS quasars with weak emission lines

Several hypotheses have been developed, but the weak line quasar (WLQ) phenomenon still remains puzzling. The aim of this study was to create a sizeable sample of WLQs and WLQ-like objects and to evaluate various properties of this sample.

We performed a search for WLQs in the spectroscopic data from the Sloan Digital Sky Survey Data Release 7 based on Kohonen self-organising maps for nearly 10^5^ quasar spectra. The final sample consists of 365 quasars in the redshift range z=0.6-4.2 (z{bar}=1.50+/-0.45) and includes in particular a subsample of 46 WLQs with equivalent widths W_MgII_<11{AA} and W_CIV_<4.8{AA} We compared the luminosities, black hole masses, Eddington ratios, accretion rates, variability, spectral slopes, and radio properties of the WLQs with those of control samples of ordinary quasars.