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Cosmology Constraints from Type Ia Supernova Simulations of the Nancy Grace Roman Space Telescope Strategy Recommended by the High Latitude Time Domain Survey Definition Committee

Richard Kessler, Rebekah Hounsell, Bhavin Joshi, David Rubin, Masao Sako, Rebecca Chen, Vivian Miranda, Benjamin. M. Rose

TL;DR

This study forecasts dark energy constraints from Type Ia supernovae observed by the Roman Space Telescope's High Latitude Time Domain Survey, complemented by LSST data. It implements an end-to-end, SNANA-based simulation + SALT3/BBC/SCONE pipeline to translate a photometric, non-spectroscopic SN sample into a $w_0$–$w_a$ cosmology, producing a Figure of Merit up to about 507 under an optimal unbinned Hubble diagram with a standard $ ext{Flat} ext{ } ext{$ ext{w}_0 ext{w}_a$CDM}$ cosmology. The analysis reveals that calibration systematics dominate FoM degradation, that non-standard cosmologies reduce FoM by roughly 25%, and that high-$z$ host-galaxy photometric redshift biases pose a key challenge requiring external optical data or improved host spectroscopy. Extended and pilot observing components offer modest gains, while a significant portion of gains hinges on reducing SN Ia training systematics and refining computation for unbinned covariances. Overall, the projected Roman+LSST SN survey promises FoM well above the mission's requirement of 326, enabling precise, model-flexible dark energy constraints.

Abstract

Within the next few years, the upcoming Nancy Grace Roman Space Telescope will be gathering data for the High Latitude Time Domain Survey (HLTDS) that will be used to significantly improve the Type Ia supernova measurement of the dark energy equation of state parameters w0 and wa. Here we generate a catalog-level simulation of the in-guide strategy recommended by the HLTDS definition committee, and determine dark energy parameter constraints using a detailed analysis that includes light curve fitting, photometric redshifts and classification, BEAMS formalism, systematic uncertainties, and cosmology fitting. After analysis and selection requirements, the sample includes 10,000 Roman SNe Ia that we combine with 4,400 events from LSST. The resulting dark energy figure of merit is well above the NASA mission requirement of 326, with the caveat that SN Ia model training systematics have not been included.

Cosmology Constraints from Type Ia Supernova Simulations of the Nancy Grace Roman Space Telescope Strategy Recommended by the High Latitude Time Domain Survey Definition Committee

TL;DR

This study forecasts dark energy constraints from Type Ia supernovae observed by the Roman Space Telescope's High Latitude Time Domain Survey, complemented by LSST data. It implements an end-to-end, SNANA-based simulation + SALT3/BBC/SCONE pipeline to translate a photometric, non-spectroscopic SN sample into a – cosmology, producing a Figure of Merit up to about 507 under an optimal unbinned Hubble diagram with a standard ext{w}_0 ext{w}_a cosmology. The analysis reveals that calibration systematics dominate FoM degradation, that non-standard cosmologies reduce FoM by roughly 25%, and that high- host-galaxy photometric redshift biases pose a key challenge requiring external optical data or improved host spectroscopy. Extended and pilot observing components offer modest gains, while a significant portion of gains hinges on reducing SN Ia training systematics and refining computation for unbinned covariances. Overall, the projected Roman+LSST SN survey promises FoM well above the mission's requirement of 326, enabling precise, model-flexible dark energy constraints.

Abstract

Within the next few years, the upcoming Nancy Grace Roman Space Telescope will be gathering data for the High Latitude Time Domain Survey (HLTDS) that will be used to significantly improve the Type Ia supernova measurement of the dark energy equation of state parameters w0 and wa. Here we generate a catalog-level simulation of the in-guide strategy recommended by the HLTDS definition committee, and determine dark energy parameter constraints using a detailed analysis that includes light curve fitting, photometric redshifts and classification, BEAMS formalism, systematic uncertainties, and cosmology fitting. After analysis and selection requirements, the sample includes 10,000 Roman SNe Ia that we combine with 4,400 events from LSST. The resulting dark energy figure of merit is well above the NASA mission requirement of 326, with the caveat that SN Ia model training systematics have not been included.

Paper Structure

This paper contains 24 sections, 8 equations, 27 figures, 7 tables.

Table of Contents

  1. Introduction
  2. Overview of Recommended HLTDS
  3. Simulation
  4. Host Galaxy
  5. Determination of Roman Exposure Times and Survey Area
  6. Visit Depths
  7. Simulation Statistics
  8. Analysis
  9. Selection Cuts and Lightcurve Fitting with SALT3
  10. Photo-$z$ Performance
  11. Photometric Classification
  12. BBC
  13. Stat+Syst Covariance Matrix
  14. Sensitivity to Host $z_{\rm phot}$ Bias
  15. Cosmology Fitting
  16. ...and 9 more sections

Figures (27)

  • Figure 1: Illustration of three survey components recommended in CCS_report.
  • Figure 2: Volumetric SNIa rate vs. redshift used in the SNANA simulation. Based on Rodney2014, and $H_0=70$ km/s/Mpc.
  • Figure 3: Blue points show host-galaxy photo-$z$ residual $\Delta_z$ (Eq. \ref{['eq:Dz']}) vs. $z_{\rm true}$ for simulated Roman events passing 2-detection trigger. Filled orange circles show mean bias and the error bars show the standard deviation in each $z_{\rm true}$ bin.
  • Figure 4: Distribution of local surface brightness mag ($m_{\rm SB}$ per arcsec$^2$) vs. redshift for 5 bands that have close overlap between HST-GOODS and Roman.
  • Figure 5: Distribution of galaxy mags in redshift range $1.5< z<2.5$ for top: simulated Roman F184-band and bottom: JWST F200W band from the PRIMER catalog. The mean and standard deviation for each distribution is shown in the legend.
  • ...and 22 more figures