Far-UV sensitivity of the Cosmic Origins Spectrograph

TL;DR

This paper reports the first measurements of the far-UV sensitivity of the Cosmic Origins Spectrograph on HST, revealing a new wavelength regime with high effective area that enables diverse astrophysical investigations.

Contribution

It provides the first characterization of COS G140L segment B's effective area in the far-UV, opening new scientific opportunities in low-redshift galaxy and intergalactic medium studies.

Findings

Effective area peaks over 1000 cm$^2$ beyond 1130 Å.

New wavelength regime for HST with high sensitivity.

Enables diverse astrophysical investigations.

Abstract

We demonstrate that the G140L segment B channel of the Cosmic Origins Spectrograph (COS) recently installed on the {\it Hubble Space Telescope (HST)} has an effective area consistent with $\sim$ 10 cm$^2$ in the bandpass between the Lyman edge at 912 \AA and Lyman $\beta$, rising to a peak in excess of 1000 cm$^2$ longward of 1130 \AA. This is a new wavelength regime for {\it 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 $< z \lesssim$ 2.8, measure the ratio of CO to H$_2$ in dense interstellar environments with $A_V >$ 3, or harness the high temperature diagnostic power of the \ion{O}{6} $\lambda\lambda$ 1032, 1038 doublet can now be carried out with unprecedented sensitivity.