A sample of weak blazars at milli-arcsecond resolution
  We started a follow-up investigation of the Deep X-ray Radio Blazar Survey
objects with declination >-10 deg. We undertook a survey with the EVN at 5GHz
to make the first images of a complete sample of weak blazars, aiming at a
comparison between high- and low-power samples of blazars. All of the 87
sources observed were detected. Point-like sources are found in 39 cases, and
48 show core-jet structure. According to the spectral indices previously
obtained, 58 sources show a flat spectral index, and 29 sources show a steep
spectrum or a spectrum peaking at a frequency around 1-2 GHz. Adding to the
DXRBS objects we observed those already observed with ATCA in the southern sky,
we found that 14 blazars and a SSRQ, are associated to gamma-ray emitters. We
found that 56 sources can be considered blazars. We also detected 2 flat
spectrum NLRGs. About 50% of the blazars associated to a gamma-ray object are
BL Lacs, confirming that they are more likely detected among blazars
gamma-emitters. We confirm the correlation found between the source core flux
density and the gamma-ray photon fluxes down to fainter flux densities. We also
found that weak blazars are also weaker gamma-ray emitters compared to bright
blazars. Twenty-two sources are SSRQs or CSSs, and 7 are GPSs. The available
X-ray ROSAT observations allow us to suggest that CSS and GPS quasars are not
obscured by large column of cold gas surrounding the nuclei. We did not find
any significant difference in X-ray luminosity between CSS and GPS quasars.
