High precision redshifts for Type Ia SNe with the Nancy Grace Roman Space Telescope prism

We present results from simulating slitless spectroscopic observations with the Nancy Grace Roman Space Telescope’s (Roman) Wide-Field Instrument (WFI) prism. The objective of this work is to quantify the efficiency of recovered type Ia supernovae (SN Ia) redshifts, as a function of prism exposure time, to guide planning for future SN Ia observing programs on Roman. Generating the 2D dispersed images and extracting 1D spectra is done with the slitless spectroscopy package pyLINEAR along with custom written software. From the analysis of ~1700 simulated SNe Ia prism spectra, we show the efficiency of recovering SNe redshifts to z≳3.0 highlighting the exceptional sensitivity of the Roman prism. We find that a 3 hour spectroscopic exposure time for prism spectra should suffice to achieve ~50 % redshift completeness for SN with 1 < z < 2. Implications for cosmological studies with Roman prism spectra of SNe Ia are also discussed.