Two New Low Redshift 21cm Absorbers

As part of a larger program to identify low redshift radio analogues of the damped Lyman−α (DLA) absorbers seen in the spectra of high redshift quasars, Westerbork Synthesis Radio Telescope (WSRT) observations have discovered two new HI 21cm absorption lines at z = 0.394 and z = 0.437 in the spectra of the radio sources B 0248+430 and B 1243-072 respectively. These sightlines and redshifts were selected for study on the basis of the previously known low ionization absorption lines of Mg ii, and neither has been observed in the Lyα line. The 21cm line observations provide information on column densities, temperatures and kinematics of the thickest cold neutral clouds in the absorbers.