Scatter broadening of compact radio sources by the ionized intergalactic medium: Prospects for detection with Space VLBI and the SKA

Understand

We investigate the feasibility of detecting and probing various components of the ionized intergalactic medium (IGM) and their turbulent properties at radio frequencies through observations of scatter broadening of compact sources.

• There is a strong case for conducting targeted observations to resolve scatter broadening (where the angular size scales as $\sim \nu^{-2}$) of compact background sources intersected by foreground galaxy haloes and rich clusters of galaxies to probe the turbulence of the ionized gas in these objects, particularly using Space VLBI with baselines of 350,000 km at frequencies below 800 MHz.
• The sensitivity of the Square Kilometre Array (SKA) allows multifrequency surveys of interstellar scintillation (ISS) of $\sim 100 \,\mu$Jy sources to detect or place very strong constraints on IGM scatter broadening down to $\sim 1\, \mu$as scales at 5 GHz.
• Scatter broadening in the warm-hot component of the IGM with typical overdensities of $\sim 30$ cannot be detected, even with Space VLBI or ISS, and even if the outer scales of turbulence have an unlikely low value of $\sim 1$ kpc.