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

Subhashis Roy1

1 National Centre for Radio Astrophysics (TIFR),
Pune University Campus, Post Bag No.3, Ganeshkhind, Pune 411 007,

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We have studied H I absorption towards three non-thermal filaments (NTFs), Sgr C, G359.54+0.18 and G359.79+0.17, using the Giant Metrewave Radio Telescope (GMRT). Our study, for the first time, constrains the distance of the Sgr C NTF and the H II region to within a few hundred parsecs of the Galactic Centre (GC). A molecular cloud with a velocity of -100 km/s appears to be interacting with the central part of the Sgr C NTF. Our study indicates that the Sgr C H II region is more distant than the Sgr C NTF and rules out any possible interaction between them. The NTF G359.54+0.18 shows weak H I absorption (4 sigma detection) at a velocity of -140 km/s, which is the velocity of a known dense molecular cloud seen towards the filament. 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 5.5 and 10.5 kpc from the sun.