Impact of DESI-ext and DESI-II redshifts on LSST SNIa cosmology

Corentin Ravoux, Philippe Gris, Damiano Rosselli, Julian Bautista, Bastien Carreres

DESI-II telecon - 23 January 2025

 

ACCEL² simulation

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

  • DESC Project: Impact of redshift host measurements from DESI and DESI-II on supernovae cosmology

SNe Ia host redshift project

  • Objectives:
    1. Number of host spectroscopic redshift measured by DESI, DESI-ext, DESI-II (+ 4MOST 4HS & CRS)
    2. Optimal strategy for DESI-II in terms of SNe Ia
    3. Improvement in term of SNe Ia cosmology
  • Complementarity with 4MOST TiDES studies (SNIa follow-up in the south)
  • DESI: Galaxy density and footprint extracted from public target
    selection only
  • DESI-II: Forecast for the low-z galaxy sample made by Noah Weaverdyck and shared between DESC and DESI
  • 4MOST:
    • 4HS: Edward Taylor and Michelle Cluver (PI)
    • CRS: Johan Richard and Jean-Paul Kneib (PI)
    • For both, agreement to use forecast in this project

Data origin

https://github.com/LSSTDESC/sn_pipe
https://github.com/corentinravoux/desidescsn/
  • Codes used:

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

SNe Ia host properties

DC2 paper 2021

Methodology:

  • Galaxy field from cosmoDC2
  • Rubin-Roman catalog:
    • SFR, Stellar mass
    • Galaxy magnitudes (LSST, SDSS, IR with Roman bands)
  • ZTF20 rate + SN Ia weights model:
R_{\mathrm{Ia}}^{A+B}\left(M_*, \mathrm{SFR}\right)=A \times M_*+B \times \mathrm{SFR}

Mannucci et al. 2005

Troxel et al. 2023

Host properties for SNe Ia in DC2

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

SNe Ia host redshift efficiency

  • Ability for a spectroscopic survey to measure redshift of a LSST SNe Ia host
  • Mathematically: proportion of LSST SNe Ia host whose redshift is measured with respect to the total number of SNe Ia, as function of redshift
R_{\mathrm{host}}(z) = R_{\mathrm{spectro}} (z) \times R_{\mathrm{SNIa}}(z)

Spectroscopic survey redshift efficiency (renormalize survey to cosmoDC2)

Proportion of SNe Ia located in the targeted host (host properties)

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

  • Target selection cuts of DESI/DESI-II/4MOST applied to cosmoDC2 galaxies

SNe Ia host redshift efficiency

R_{\mathrm{host}}(z) = R_{\mathrm{spectro}}(z) \times R_{\mathrm{SNIa}}(z)
R_{\mathrm{spectro}}(z) = \frac{N_{\mathrm{gal}}(z)_{\mathrm{survey}}}{N_{\mathrm{gal}}(z)_{\mathrm{dc2,cut}}}
R_{\mathrm{SNIa}}(z) = \frac{N_{\mathrm{host}}(z)_{\mathrm{dc2,cut}}}{N_{\mathrm{host}}(z)_{\mathrm{dc2}}}

Proportion, not absolute number

SNe Ia proportion located in the targeted host

Spectroscopic survey redshift efficiency

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

DESI-II strategy variation

  • From the work of Noah Weaverdyck and help from Sven Heydenreich: DESI-II strategies for a low-z complete galaxy sample, with fixed amount of observation time
  • Variation on maximal magnitude targeted, density and exposure time per spectrum

Less spectra but deeper

More spectra but shallower

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

Impact on SNIa dark energy constraints

Gris Regnault et al. 2022, Gris et al. 2024

  • SMoM: metric to evaluate the impact of observation strategy on SNIa (Ω,w) constraints

 

  • Changing the spectroscopic scenario in sn_pipe pipeline

DESI, DESI-ext, DESI-II spectroscopic scenario

(4MOST TiDES included)

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

  • Baseline: redshifts from 4MOST TiDES and Subaru (in COSMOS XMM DDF)
  • Photo-z not considered here
  • One DESI-II strategy
  • Large increase in SN Ia host redshifts

Impact on SNIa dark energy constraints

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

  • Baseline: redshifts from 4MOST TiDES and Subaru (in COSMOS XMM DDF)
  • Photo-z not considered here
  • One DESI-II strategy
  • Up to 20 % improvement on w error compare to baseline

Impact on SNIa dark energy constraints

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

  • 8 OuterRim simulations with LSST SNe Ia observation strategy
  • Measurement of fσ8 with SNe Ia peculiar velocities
  • Inclusion of different spectroscopic scenarios

Impact on SNIa growth rate constraints

Measurement improved by DESI (~4 %), not much by DESI-II (~0.5%)

Rosselli et al. in prep.

Corentin Ravoux                                                                                                                                                                     DESI-II telecon - January 2025

ACCEL² simulation

  • Improvement of LSST SNIa dark energy contrast from spectroscopic sample with DESI, DESI-ext and DESI-II redshifts
  • Not a large improvement on peculiar velocity studies mainly sensitive to low redshifts

Conclusion

Hypothesis for DESI

  • Hypothesis to select the galaxy population observed by DESI in the cosmoDC2 simulation:
    • Strongest hypothesis: fiber magnitude not calculated on cosmoDC2
    • BGS: main magnitude cut r < 20.175, no star-galaxy separation (star not accounted in DC2), no very bright color cut, no bright/faint differenciation
    • LRG: LRG South magnitude & color cuts
    • DESI-ext: same selection as DESI
    • DESI-II: magnitude cut depending on DESI-II strat and color cuts:
\begin{split} &\left(z - W_1\right) > 0.8 \left( r - z \right) -0.6 \\ &g-W_1 > 2.9\ \mathrm{OR}\ r - W_1 > 1.8 \end{split}

Other plots

Other plots