Cosmology with the Nancy Grace Roman Space Telescope prism

The Nancy Grace Roman Space Telescope, to be launched in mid-2020s, will be equipped with a Wide Field Instrument (WFI) that consist of seven imaging filters covering 750–2000 nm, a slitless grism and prism for spectroscopy, and eighteen 4k×4k H4RG HgCdTe detectors that comprises the focal plane array covering a field of view of 0.28 square degrees. The Roman cosmology program, aimed to elucidate on the nature of dark energy, will use WFI to conduct high-latitude surveys of galaxies and lensing, as well Type Ia Supernova (SN Ia) surveys.

As a part of our efforts to understand the improvements that the prism can bring to SN Ia cosmology and to understand the sources of systematic uncertainties that may appear, we use spectra templates to simulate SNe spectra through the Roman Space Telescope optical path using the most current characterization of the optical system and detectors. We use realistic noise model based on the known properties of the detector.

We analyze the resulting noisy-spectra and evaluate how well we can recover the parameters of supernovae given the statistical and systematic uncertainties as well as observing strategies. A prediction of the overall Dark Energy Task Force figure of merit will also be presented. We find that space-based SN Ia spectroscopy using the slitless prism provides additional information that could not be obtained using imaging alone. This includes not only a better estimate of the redshifts but also improved SNe classification (typing and sub-typing). Systematic uncertainties present in imaging-only surveys are also addressed in prism observations.