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.

e-MERLIN observations at 5 GHz of the GOODS-N region: pinpointing AGN cores in high redshift galaxies

We present 5 GHz e-MERLIN observations of the GOODS-N region at sub-arcsec resolution (0.2--0.5 arcsec). These data form part of the early commissioning observations for the e-MERLIN interferometer and a pilot for the e-MERLIN legacy program eMERGE. A total of 17 sources were detected with S/N>3. These observations provide unique information on the radio source morphology at sub-arcsec scales. For twelve of these sources, deeper 1.4 GHz MERLIN+VLA observations at the same spatial resolution are available, allowing radio spectral indices to be derived for ten sources on sub-arcsec angular scales. Via analysis of the spectral indices and radio morphologies, these sources have been identified as AGN cores in moderate-to-high redshift (1<z<4) galaxies. These results have provided AGN (or AGN candidate) classification for six previously unclassified sources and confirmed the AGN nature of the rest of the sample. Ultimately the eMERGE project will image the GOODS-N region at 1.4 and 5 GHz with higher resolution (about 50 mas at 5 GHz) and down to sub-microJy sensitivities. The unique combination of sensitivity and spatial resolution will be exploited to study star formation and AGN activity in distant galaxies.