Radio Emission from Broad Absorption Line Quasars

Abstract

Broad Absorption Line Quasars (BALQs) generally exhibit significant outflows that may interact with the surrounding medium, resulting in radio emission. We selected a sample of 13 powerful radio-quiet (RQ) BALQs, where the UV outflow kinetic power is measurable, and detected nine of them with the Very Large Array A configuration at 5.5 GHz and 9.0 GHz. The radio emission is mostly unresolved and is generally constrained within a scale of < 1--4 kpc. In the nine detected objects, the radio spectral slope alpha_5.5-9.0 is steep (< -0.5) in five objects and is flat or inverted (> -0.5) in four objects. We discuss how the steep-slope emission can be associated with the UV outflows, and how the flat-slope emission can be intrinsically steep but flattened by free-free absorption from the UV outflowing gas. However, we find no correlation between the radio luminosity and the estimated outflow kinetic power, which suggests that the outflows are likely not a major source of the observed radio emission. In addition, the radio loudness of these RQ BALQs is comparable to that of typical RQ quasars, implying that the UV outflows likely do not produce stronger radio emission compared to non-BALQs. Follow-up radio observations can test the free-free absorption interpretation and can be used as a new probe for outflows in AGN.