Constraints on distances to Galactic Centre non-thermal filaments from HI absorption

We have studied HI absorption towards three non-thermal filaments (NTFs) Sgr C, G359.54+0.18and G359.79+0.17using the Giant Metrewave Radio Telescope (GMRT). Our study, for the first time, constrains the distance of the Sgr CNTF and the HII region seen associated with the NTF in the sky plane, to within a few hundred parsecs from the Galactic Centre (GC). A molecular cloud with a velocity of -100 km s ^-1appears to be associated with the central part of the Sgr CNTF. Our study also indicates that the Sgr CHII region is relatively farther away than the NTF along our line of sight, and thereby provides evidence against any possible interaction between the two objects. The NTF G359.54+0.18shows weak HI absorption (4 (sigma) detection) at a velocity of -140 km s^ -1, which is the velocity of a known dense molecular cloud seen towards the NTF. This cloud is expected to be located within ~200 pc of the GC and thereby provides a lower limit to the distance. The upper limit to the distance of this NTF from the Sun is 10.5 kpc. The distance to the NTF G359.79+0.17 is between 5.1 and 10.5 kpc from the Sun