Bignall, HayleyKoay, Jun YiLovell, JimJauncey, DaveMacquart, Jean-PierrePursimo, TapioOjha, RoopeshRickett, BarneyKedziora-Chudczer, LucynaReynolds, CormacKhoo, Sue2020-04-272020-04-272012-04-17Bignall, Hayley; Koay, Jun Yi; Lovell, Jim; Jauncey, Dave; Macquart, Jean-Pierre; Pursimo, Tapio; Ojha, Roopesh; Rickett, Barney; Kedziora-Chudczer, Lucyna; Reynolds, Cormac; Khoo, Sue; An update on MASIV: How intrinsic properties influence interstellar scintillation of AGN; Resolving the Sky - Radio Interferometry: Past, Present and Future -RTS2012; https://pos.sissa.it/163/015/pdfhttp://hdl.handle.net/11603/18335Resolving the Sky - Radio Interferometry: Past, Present and Future -RTS2012 April 17-20, 2012 Manchester, UKMany flat-spectrum AGN exhibit short timescale variations when observed at radio wavelengths, due to interstellar scintillation (ISS). The observed variations depend on source angular size and "core dominance", as well as on the scattering properties of the intervening interstellar medium, both of which are highly non-uniform when considering large samples. ISS offers a powerful probe of source structure on micro-arcsecond angular scales. However, in order to use the statistics of ISS as a probe, it is necessary to understand the selection effects in the AGN samples under study. One initially surprising result of the MASIV 5 GHz VLA Survey was a drop-off in the ISS amplitudes of sources above z=2. In order to determine the cause of this effect, follow-up VLA observations were conducted at two frequencies. Our sample shows on average a steepening of source spectral index with redshift. Careful analysis shows that, after accounting for the redshift-spectral index correlation, the redshift dependence of ISS can be successfully modelled by the expected (1 + z)⁰˙⁵ scaling of intrinsic angular sizes of a flux- and intrinsic brightness temperature-limited sample. The MASIV follow-up observations allow limits to be placed on angular broadening due to interstellar and intergalactic scattering, beyond the resolution achievable with ground-based VLBI.8 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)Text