The Quasar Feedback Survey: zooming into the origin of radio emission with e-MERLIN

Abstract

We present 6 GHz e-MERLIN observations of 42 z < 0.2 type 1 and type 2 mostly radio-quiet quasars (⁠L _[oIII]  ≥ 104² erg s^-1; L _AGN ≥  10⁴⁵erg s^-1) from the Quasar Feedback Survey. The nature and origin of radio emission in these types of sources is typically ambiguous based on all-sky, low-resolution surveys. With e-MERLIN, we investigate radio emission on sub-kiloparsec scales (⁠~10s–100s pc). We find 37/42 quasars are detected, with a diversity of radio morphologies, including compact cores, knots, and extended jet-like structures, with sizes of 30–540 pc. Based on morphology and brightness temperature, we classify 76 per cent of the quasars as radio-AGN, compared to the ~57 per cent identified as radio-AGN at the ~1–60 kpc scales probed in prior studies. Combining results from e-MERLIN and the Very Large Array, 86 per cent reveal a radio-AGN. On average, ~60 per cent of the total radio flux is resolved away in the e-MERLIN maps, and is likely dominated by jet-driven lobes and outflow-driven shocks. We find no significant differences in measured radio properties between type 1 and type 2 quasars, and estimate sub-relativistic jet speeds of ~0.2–0.3c and modest jet powers of Pjet≈10⁴³erg s^-1 for the few targets, where these measurements were possible. These quasars share characteristics with compact radio-selected populations, and the global radio emission likely traces strong interactions between the AGN (jets/outflows) and their host galaxy ISM from 10s parsec to 10s kiloparsec scales.

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