2011MNRAS.418.2032V

We have analysed the spatially integrated kinematic properties of the ionized gas within the inner r ≲ few kpc in 13 optically selected SDSS type 2 quasars at z ∼ 0.3–0.6, using the [O III]λλ4959,5007 lines. The line profiles show a significant asymmetry in 11 objects. There is a clear preference for blue asymmetries, which are found in 9/13 quasars at 10 per cent intensity level. In coherence with studies on other types of active and non active galaxies, we propose that the asymmetries are produced by outflows where differential dust extinction is at work.

This scenario is favoured by other results we find: in addition to quiescent ambient gas, whose kinematic properties are consistent with gravitational motions, we have discovered highly perturbed gas in all objects. This gas emits very broad lines (R = FWHM[O_III]/FWHM_stars ≳ 2). While the quiescent gas shows small or null velocity shifts relative to the systemic velocity, the highly perturbed gas trends to show larger shifts which, moreover, are blueshifts in general. Within a given object, the most perturbed gas trends to have the largest blueshift as well. All together support that the perturbed gas, which is responsible for the blue asymmetries of the line profiles, is outflowing. The outflowing gas is located within the quasar ionization cones, in the narrow line region.

The relative contribution of the outflowing gas to the total [O III] line flux varies from object to object in the range ∼ 10–70 per cent. An anticorrelation is found such that, the more perturbed the outflowing gas is, the lower its relative contribution is to the total [O III] flux. This suggests that outflows with more perturbed kinematics involve a smaller fraction of the total mass of ionized gas.

Although some bias affects the sample, we argue that ionized gas outflows are a common phenomenon in optically selected type 2 quasars at 0.3 ≲ z ≲ 0.6.

Based on observations carried out at the European Southern Observatory (Paranal, Chile) with FORS2 on VLT-UT1 (programmes 081.B-0129 and 083.B-0381).