Peculiar-velocity cosmology with Types Ia and II supernovae

ABSTRACT We present the Democratic Samples of Supernovae (DSS), a compilation of 775 low-redshift Type Ia and II supernovae (SNe Ia and II), of which 137 SN Ia distances are derived via the newly developed snapshot distance method. Using the objects in the DSS as tracers of the peculiar-velocity field, we compare against the corresponding reconstruction from the 2M++ galaxy redshift survey. Our analysis – which takes special care to properly weight each DSS subcatalogue and cross-calibrate the relative distance scales between them – results in a measurement of the cosmological parameter combination f ₈ = 0. 390-₀. ₀₂₂^+0. 022 as well as an external bulk flow velocity of 195-₂₃^+22 km s−1 in the direction (, b) = (292-₇^+7, -6-₄^+5) deg, which originates from beyond the 2M++ reconstruction. Similarly, we find a bulk flow of 245-₃₁^+32 km s−1 towards (, b) = (294-₇^+7, 3-₅^+6) deg on a scale of 30\, h^-1 Mpc if we ignore the reconstructed peculiar-velocity field altogether. Our constraint on fσ8 – the tightest derived from SNe to date (considering only statistical error bars), and the only one to utilize SNe II – is broadly consistent with other results from the literature. We intend for our data accumulation and treatment techniques to become the prototype for future studies that will exploit the unprecedented data volume from upcoming wide-field surveys.