Helium line detections from ELDWIM at 1.4 GHz

TL;DR

This study reports helium line detections in the ELDWIM of the Galaxy at 1.4 GHz, using WSRT observations towards 11 Galactic positions, and explores the correlation with nearby HII regions.

Contribution

First detection of helium lines from ELDWIM at 1.4 GHz towards multiple Galactic positions and analysis of their association with surrounding HII regions.

Findings

Helium lines detected in 5 out of 11 positions with high confidence.

Detection likelihood increases with proximity and characteristics of HII regions.

Helium line detection correlates with the ionization state influenced by HII regions.

Abstract

Helium line observations towards 11 Galactic positions using Westerbork Synthesis Radio Telescope(WSRT) have been reported. These observations were made towards nearby positions where already hydrogen lines were detected at sufficiently high intensity($\geq$50mK) at 1.4 GHz. This approach gave a fair chance for the detection of helium line as well, keeping in mind the relative abundance(10%) of helium with respect to hydrogen. Care was also taken to avoid the presence of HII regions along the line of sight so that the line emission originates from the extended diffuse low density ionized component, ELDWIM of the Galaxy. The observations have resulted in the detection of helium line towards 5 positions out of 11 with signal to noise ratio(snr) $>$ 4$\sigma$. An attempt has been made to associate detection/non-detection of helium line to the presence of surrounding HII regions. A weighting scheme that accounts for nearby($<$ 500pc) HII regions, their distances and other factors produces favourable results. It is seen from this weighting scheme that a higher weight favours the detection of helium line while lower weight is associated with non-detection. The idea is to correlate ionization of ELDWIM with the surrounding HII regions.