Correcting for peculiar velocities of Type Ia supernovae in clusters of galaxies

Abstract

Context. Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the Universe. To perform such measurements the luminosity and cosmological redshift (z) of the SNe Ia have to be determined. The uncertainty on z includes an unknown peculiar velocity, which can be very large for SNe Ia in the virialized cores of massive clusters. Aims. We determine which SNe Ia exploded in galaxy clusters. We then study how the correction for peculiar velocities of host galaxies inside the clusters improves the Hubble residuals. Methods. Using 145 SNe Ia from the Nearby Supernova Factory we found 11 candidates for membership in clusters. To estimate the redshift of a cluster we applied the bi-weight technique. Then, we use the galaxy cluster redshift instead of the host galaxy redshift to construct the Hubble diagram. Results. For SNe Ia inside galaxy clusters the dispersion around the Hubble diagram when peculiar velocities are taken into account is smaller in comparison with a case without peculiar velocity correction, with a wRMS =0.130 ± 0.038 mag instead of wRMS =0.137 ± 0.036 mag. The significance of this improvement is 3.58 σ. If we remove the very nearby Virgo cluster member SN2006X (z < 0.01) from the analysis, the significance decreases to 1.34 σ. The peculiar velocity correction is found to be highest for the SNe Ia hosted by blue spiral galaxies, with high local specific star formation rate and smaller stellar mass, seemingly counter to what might be expected given the heavy concentration of old, massive elliptical galaxies in clusters. Conclusions. As expected, the Hubble residuals of SNe Ia associated with massive galaxy clusters improve when the cluster redshift is taken as the cosmological redshift of the SN. This fact has to be taken into account in future cosmological analyses in order to achieve higher accuracy for cosmological redshift measurements. Here we provide an approach to do so.

Influence of Type Ia Supernova Environment and Their Peculiar Velocities on Distance measurements

“…Using 145 SNe Ia from the Nearby Supernova Factory 11 candidates for membership in clusters were found. It was shown that for SNe Ia inside galaxy clusters the dispersion around the Hubble diagram when peculiar velocities are taken into account is smaller in comparison with a case without peculiar velocity correction, with a wRMS = 0.130 ± 0.038 mag instead of wRMS = 0.137 ± 0.036 mag [2]. However, this study was done with nearby sample of supernovae.…”

“…If we transform this dispersion into a magnitude error, we will see that for lowredshift region (z < 0.05) this error is several times more than the one corresponding to 150 km s −1 and 300 km s −1 , moreover, it is two times larger than the intrinsic dispersion of SNe Ia around the Hubble diagram (0.11 mag, see fig. 2 in [2]). It means that standard methods for peculiar velocity correction do not work for the galaxies inside the clusters and another, more accurate method has to be developed.…”

“…To better estimate the cosmological redshift of the SNe Ia that were exploded in cluster of galaxies, the peculiar velocity correction can be introduced [2]. For a SN in a cluster it is possible to estimate z c more accurately using the host galaxy cluster redshift (z cl ) instead of the host redshift (z host ).…”

“…SN2006X is presented in the inset plot separately from the others due to its very large offset. The figure is taken from[2].…”

Peculiar velocities of supernovae Ia in clusters of galaxies

“…Среди сверхновых Pantheon 297 объектов имеют красное смещение z < 0.15. Для таких СН вклад пекулярных скоростей наиболее значим [1] (рис. 1).…”