Understanding the properties of sub-arcsecond scale compact sources at low radio frequencies

We present new means of identifying and studying large number of sub-arcsecond scale compact sources at low radio frequencies (<300 MHz). Conventional efforts using Very Long Baseline Interferometry observations (VLBI), in order to gain the relevant angular resolution scales, are limited to observing objects individually which very quickly results in large overheads in time. We have highly improved the efficiency of compact source identification through the observations of interplanetary scintillation on the wide field-of-view (900 sq. degrees) of the Murchison widefield array (MWA) at 162 megahertz, thus, effectively converting the MWA (maximum baseline of 6 km, angular resolution ~1 arcminute) into a VLBI instrument with >300 km baselines. From very short observations (~5–10 minutes), we are able to identify sub-arcsecond scale structures in ~300 objects, and place constraints on angular size scales of compact structures in >2000 objects. Such efficiency now enables investigations of compact sources at low radio frequencies in unprecedented numbers. We have studied the properties of the compact sources at low frequencies, and have identified the potential to find very interesting objects in both galactic (pulsars) and extragalactic (e.g. objects at very high redshifts) parts of the sky. From our investigations of the source populations, we have shown that the compact source populations at low frequencies are dominated by the family of peaked spectrum sources. This is unlike the scenario at high radio frequencies (>10 gigahertz) where the population of compact sources is almost entirely composed of (often beamed) compact cores of radio galaxies. In this talk, I will provide an overview of our technique, our results and an update on our efforts to cover very wide parts of the sky.