Measuring the growth rate of structure with Type IA Supernovae from LSST

TL;DR

This paper explores how Type Ia supernovae observed by LSST can be used to measure the growth rate of cosmic structure, potentially surpassing traditional methods like RSD, especially when combined with galaxy redshift data.

Contribution

It introduces new methods for using LSST supernovae to constrain the growth rate of structure, demonstrating their potential to outperform existing techniques.

Findings

Supernovae can provide more precise growth rate constraints than RSD at z<0.5.

Combining supernovae with galaxy redshifts enhances the measurement accuracy.

Predicted large samples of supernova host redshifts will significantly improve large-scale gravity tests.

Abstract

We investigate measuring the peculiar motions of galaxies up to $z=0.5$ using Type Ia supernovae (SNe Ia) from LSST, and predict the subsequent constraints on the growth rate of structure. We consider two cases. Our first is based on measurements of the volumetric SNe Ia rate and assumes we can obtain spectroscopic redshifts and light curves for varying fractions of objects that are detected pre-peak luminosity by LSST (some of which may be obtained by LSST itself and others which would require additional follow-up). We find that these measurements could produce growth rate constraints at $z<0.5$ that significantly outperform those using Redshift Space Distortions (RSD) with DESI or 4MOST, even though there are $\sim4\times$ fewer objects. For our second case, we use semi-analytic simulations and a prescription for the SNe Ia rate as a function of stellar mass and star formation rate to predict the number of LSST SNe IA whose host redshifts may already have been obtained with the Taipan+WALLABY surveys, or with a future multi-object spectroscopic survey. We find $\sim 18,000$ and $\sim 160,000$ SN Ia with host redshifts for these cases respectively. Whilst this is only a fraction of the total LSST-detected SNe Ia, they could be used to significantly augment and improve the growth rate constraints compared to only RSD. Ultimately, we find that combining LSST SNe Ia with large numbers of galaxy redshifts will provide the most powerful probe of large scale gravity in the $z<0.5$ regime over the coming decades.