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We cross‐correlate the  Fermi  11‐month survey (1FGL) catalogue with the 20‐GHz Australia Telescope Compact Array (AT20G) radio survey catalogue composed of 5890 sources at declination  &lt; 0° . Among the 738  Fermi  sources distributed in the southern sky, we find 230 highly probable candidate counterparts in the AT20G survey. Of these, 222 are already classified in the  Fermi  one‐year Large Area Telescope (LAT) active galactic nucleus (AGN) catalogue (1LAC) as blazars [either flat spectrum radio quasars (FSRQs) or BL Lacertae objects (BL Lacs)], AGNs or sources of unknown class but with an associated counterpart, while eight are new associations. By studying the γ‐ray and radio properties of these associations, we find a correlation between the γ‐ray flux (above 100 MeV) and the 20‐GHz flux density. This correlation is more than 3σ statistically significant, both for the population of BL Lacs and for FSRQs considered separately. We also find that the radio counterparts associated with the  Fermi  sources have, on average, flat radio spectra between 5 and 20 GHz and that  Fermi γ‐ray sources are not preferentially associated with ‘ultra‐inverted spectrum’ radio sources. For two of the eight new associations, we build the broad‐band spectral energy distribution combining  Fermi ,  Swift  and radio observations. One of these two sources is identified with the high‐redshift FSRQ Swift J1656.3–3302  ( z = 2.4)  and we classify the other source as a candidate new FSRQ. We also study the brightest radio source of the 46 associations without an optical classification and classify it as a new BL Lac candidate ‘twin’ of the prototypical BL Lac OJ 287 if its redshift is larger,   z ∼ 0.4 .

Correlation of Fermi Large Area Telescope sources with the 20‐GHz Australia Telescope Compact Array radio survey