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

¹ Université Clermont Auvergne, CNRS/IN2P3, Laboratoire de Physique de Clermont, 63000 Clermont-Ferrand, France
e-mail: pierrefrancois.leget@gmail.com
² Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, Stanford University, Stanford, CA 94305, USA
³ Lomonosov Moscow State University, Sternberg Astronomical Institute, Universitetsky pr. 13, Moscow 119234, Russia
⁴ Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
⁵ Laboratoire de Physique Nucléaire et des Hautes Énergies, Université Pierre et Marie Curie Paris 6, Université Paris Diderot Paris 7, CNRS-IN2P3, 4 place Jussieu, 75252 Paris Cedex 05, France
⁶ Department of Physics, Yale University, New Haven, CT 06250-8121, USA
⁷ Department of Physics, University of California Berkeley, 366 LeConte Hall MC 7300, Berkeley, CA 94720-7300, USA
⁸ Université de Lyon, Université de Lyon 1, Villeurbanne, CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 69622 Lyon, France
⁹ Department of Physics and Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK
¹⁰ The Oskar Klein Centre, Department of Physics, AlbaNova, Stockholm University, 106 91 Stockholm, Sweden
¹¹ Aix-Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288 Marseille, France
¹² Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹³ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102 Goleta, CA 93117, USA
¹⁴ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
¹⁵ Institut fũr Physik, Humboldt-Universitãt zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
¹⁶ Deutsches Elektronen-Synchrotron, 15735 Zeuthen, Germany
¹⁷ Tsinghua Center for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁸ Centre de Recherche Astronomique de Lyon, Université Lyon 1, 9 Avenue Charles André, 69561 Saint-Genis-Laval, France
¹⁹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁰ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
²¹ Computational Cosmology Center, Computational Research Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road MS 50B-4206, Berkeley, CA 94720, USA
²² Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan

Received: 1 March 2018
Accepted: 6 April 2018

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 using 145 SNe Ia from the Nearby Supernova Factory. We then study how the correction for peculiar velocities of host galaxies inside the clusters improves the Hubble residuals.

Methods. We found 11 candidates for membership in clusters. We applied the biweight technique to estimate the redshift of a cluster. Then, we used 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 compared with a case without peculiar velocity correction, which has a wRMS = 0.130 ± 0.038 mag instead of wRMS = 0.137 ± 0.036 mag. The significance of this improvement is 3.58σ. If we remove the very nearby Virgo cluster member SN2006X (z < 0.01) from the analysis, the significance decreases to 1.34σ. The peculiar velocity correction is found to be highest for the SNe Ia hosted by blue spiral galaxies. Those SNe Ia have high local specific star formation rates and smaller stellar masses, which is 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 supernova. This fact has to be taken into account in future cosmological analyses in order to achieve higher accuracy for cosmological redshift measurements. We provide an approach to do so.