2010ApJ...709L.183M

We demonstrate that the G140L Segment B channel of the Cosmic Origins Spectrograph recently installed on the Hubble Space Telescope (HST) has an effective area consistent with ∼10 cm2 in the bandpass between the Lyman edge at 912 Å and Lyman β, rising to a peak in excess of 1000 cm2 longward of 1130 Å. This is a new wavelength regime for HST and will allow opportunities for unique science investigations. In particular, investigations seeking to quantify the escape fraction of Lyman continuum photons from galaxies at low redshift, determine the scale length of the hardness variation in the metagalactic ionizing background over the redshift range 2 <z≲ 2.8, or measure the ratio of CO to H₂ in dense interstellar environments with A_V> 3 can now be carried out with unprecedented sensitivity.