Giant Radio Galaxies as a Probe of the Cosmological Evolution of the IGM I. Preliminary Deep Detections and Low-Resolution Spectroscopy with SALT

A problem of the cosmological evolution of the intergalactic medium (IGM) is recalled and a necessity to find distant (z>0.5) "giant" radio galaxies (GRGs) with the lobe energy densities lower than about 10-14 J/m3 to solve this problem is emphasized. Therefore we undertake a search for such GRGs on the southern sky hemisphere using SALT. In this paper we present a selected sample of the GRG candidates and the first deep detections of distant host galaxies, as well as the low-resolution spectra of the galaxies identified on the DSS frames. The data collected during the Performance Verification (P-V) phase show that 21 of 35 galaxies with the spectroscopic redshift have the projected linear size greater than 1 Mpc (for H0=71 km/s Mpc). However their redshifts do not exceed the value of 0.4 and the energy density in only two of them is less than 10-14 J/m3. A photometric redshift estimate of one of them (J1420-0545) suggests a linear extent larger than 4.8 Mpc, i.e., larger than that of 3C236, the largest GRG known up to now.