Redshift Properties of MASIV sources

The MASIV 5 GHz VLA flat-spectrum radio source variability survey of the northern sky has discovered that more than half of its 475 targets exhibited interstellar scintillation (ISS) at one or more of the four survey epochs. vVe present the first results of the spectroscopic identifications of the sample. For 253 sources the spectroscopic identification is obtained and evaluated from the literature. For 76 sources in the RA range 13h _24h we use data from our own observations with the Nordic Optical Telescope and the Palomar Hale Telescope. Based on their optical spectrum and luminosity, the majority of the sources are QSOs. However there are many BL Lac objects and some narrow line/weak AGN in the sample. The BL Lac fraction appears to be much higher amongst the ISS than non-ISS sources and most other type of AGN than BL Lac or FSRQ are non-ISS sources, which indicates a higher incidence of bright, compact cores in BL Lacs. Our results show that ISS sources have a flat redshift distribution in comparison to the non-ISS sources. Particularly intriguing is a lack of z >2 ISS sources in the MASIV sample, which may be explained by the scattering properties of the Intergalactic Medium. The radio and optical luminosities ofISS and non-ISS sources are similar. Finally, we find that about 50% of the ISS sources with 85 GHz > 0.3.Iy are LAT-detected in comparison to a 25% detection rate of the non-ISS sources.