The Search for HI Emission at z $\approx0.4$ in Gravitationally Lensed Galaxies with the Green Bank Telescope

TL;DR

This study attempts to detect neutral hydrogen in gravitationally lensed galaxies at z~0.4 using the Green Bank Telescope, employing novel RFI mitigation techniques to improve sensitivity and set upper limits on HI mass.

Contribution

First use of gravitational lensing with GBT to search for HI emission at z~0.4, introducing effective RFI removal methods to enhance detection capabilities.

Findings

Set upper limits on HI mass at z=0.398 and z=0.487

Reduced spectral noise by ~25% using new RFI mitigation

Demonstrated techniques to study faint, distant galaxies' HI content

Abstract

Neutral Hydrogen (HI) provides a very important fuel for star formation, but is difficult to detect at high redshift due to weak emission, limited sensitivity of modern instruments, and terrestrial radio frequency interference (RFI) at low frequencies. We the first attempt to use gravitational lensing to detect HI line emission from three gravitationally lensed galaxies behind the cluster Abell 773, two at redshift of 0.398 and one at z=0.487, using the Green Bank Telescope. We find a 3 sigma upper limit for a galaxy with a rotation velocity of 200 km/s is M_HI=6.58x10^9 and 1.5x10^10 M_solar at z=0.398 and z=0.487. The estimated HI masses of the sources at z=0.398 and z=0.487 are a factor of 3.7 and ~30 times lower than our detection limits at the respective redshifts. To facilitate these observations we have used sigma clipping to remove both narrow- and wide-band RFI but retain the signal from the source. We are able to reduce the noise of the spectrum by ~25% using our routine instead of discarding observations with too much RFI. The routine is most effective when ~10 of the integrations or fewer contains RFI. These techniques can be used to study HI in highly magnified distant galaxies that are otherwise too faint to detect.