Correlation of Fermi-LAT sources with the AT20GHz radio survey
  We cross correlate the Fermi 11 months survey catalogue (1FGL) with the 20
GHz Australia Telescope Compact Array radio survey catalogue (AT20G) composed
by 5890 sources at declination <0 deg. 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 as blazars (176 of known
type and 46 of unknown optical class) in the Fermi 1-year LAT AGN Catalogue
(1LAC) and 8 are new associations. By studying the gamma-ray and radio
properties of these associations we find a strong correlation between the
gamma-ray flux (above 100 MeV) and the 20 GHz flux density. This correlation is
more than 3 sigma statistically significant both for the population of BL Lacs
and of FSRQ considered separately. We also find that the radio counterparts
associated to the Fermi sources have on average flat radio spectra between 5
and 20 GHz and that Fermi gamma-ray sources are not preferentially associated
with "ultra inverted spectrum" radio sources. For 2 of the 8 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 somewhat
larger, z~0.4.
