Detecting cold gas at intermediate redshifts: Giant metrewave radio telescope survey using Mg II systems

Abstract

Intervening H I 21 cm absorption systems at z ≥ 1.0 are very rare, and only four confirmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the interstellar medium of high-z galaxies. Moreover, they can provide independent constraints on the variation of fundamental constants. We report three new detections based on our ongoing Giant Metrewave Radio Telescope (GMRT) survey for 21 cm absorbers at 1.10 ≤ z_abs ≤ 1.45 from candidate damped Lya systems. The 21 cm lines are narrow for the z_abs = 1.3710 system toward SDSS J0108-0037 and z_abs = 1.1726 system toward SDSS J2358-1020. Based on line FWHM, the kinetic temperatures are ≤5200 and ≤800 K, respectively. The 21 cm absorption profile of the third system, z_abs = 1.1908 system toward SDSS J0804+3012, is shallow, broad, and complex, extending up to 100 km s^-1. The centroids of the 21 cm lines are found to be shifted with respect to the corresponding centroids of the metal lines derived from SDSS spectra. This may mean that the 21 cm absorption is not associated with the strongest metal-line component.