Giant Radio Galaxies: I. Intergalactic Barometers
  We present new wideband radio observations with the Australia Telescope
Compact Array of a sample of 12 giant radio galaxies. The radio observations
are part of a larger radio-optical study aimed at relating the radio structures
with the ambient medium on large scales. With projected linear sizes larger
than 0.7 Mpc, these objects are ideal candidates for the study of the Warm-Hot
Intergalactic Medium (WHIM). The sample includes sources with sizes spanning
0.8 to 3.2 Mpc and total powers of 1.2*10^24 to 4.0*10^26 W Hz^-1 at 2.1 GHz.
Redshifts were limited to z<0.15 to permit spectroscopic observations of the
hosts and neighbouring galaxies, which were obtained using the AAOmega
spectrograph on the Anglo-Australian Telescope. We derive lobe energy densities
from the radio observations via equipartition arguments. The inferred pressures
in the lobes of the giant radio sources, which range from 1.1*10^-15 to
2.0*10^-14 Pa (80 to 1500 cm^-3 K), are lower than previously inferred from
X-ray observations of dense filaments. Comparison with the OverWhelmingly Large
Simulations (OWLS) suggests that the WHIM in pressure balance with the radio
lobes has a temperature in excess of ~10^6.5 K or a particle overdensity in the
range 50 to 500. This study highlights the capability of next generation
surveys, such as the Evolutionary Map of the Universe (EMU) survey with the
Australian Square Kilometre Array Pathfinder (ASKAP), to study populations of
giant radio sources at lower surface brightness and thereby discriminate
between models for the cosmological evolution of the intergalactic medium and
examine the validity of cosmological hydrodynamical simulations.
