Measuring cosmic bulk flows with Type Ia supernovae from the Nearby Supernova Factory

¹ Physikalisches Institut, Universität Bonn, Nußallee 12, 53115 Bonn, Germany
e-mail: feindt@physik.uni-bonn.de; mkersch@physik.uni-bonn.de
² Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
³ 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
⁴ Department of Physics, Yale University, New Haven, CT, 06250-8121, USA
⁵ Research School of Astronomy and Astrophysics, Australian National University, ACT 2611 Canberra, Australia
⁶ Université de Lyon, Université de Lyon 1, Villeurbanne, CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 69622 Lyon, France
⁷ Department of Physics, University of California Berkeley, 366 LeConte Hall MC 7300, Berkeley, CA 94720-7300, USA
⁸ Computational Cosmology Center, Computational Research Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road MS 50B-4206, Berkeley, CA 94720, USA
⁹ Department of Astronomy, B-20 Hearst Field Annex # 3411, University of California, Berkeley, CA 94720-3411, USA
¹⁰ Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA
¹¹ Centre de Recherche Astronomique de Lyon, Université Lyon 1, 9 Avenue Charles André, 69561 Saint-Genis-Laval Cedex, France
¹² Centre de Physique des Particules de Marseille, 163 avenue de Luminy, Case 902, 13288 Marseille Cedex 09, France
¹³ Tsinghua Center for Astrophysics, Tsinghua University, 100084 Beijing, PR China
¹⁴ Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003, USA
¹⁵ National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, PR China

Received: 12 May 2013
Accepted: 10 October 2013

Abstract

Context. Our Local Group of galaxies appears to be moving relative to the cosmic microwave background with the source of the peculiar motion still uncertain. While in the past this has been studied mostly using galaxies as distance indicators, the weight of Type Ia supernovae (SNe Ia) has increased recently with the continuously improving statistics of available low-redshift supernovae.

Aims. We measured the bulk flow in the nearby universe (0.015 < z < 0.1) using 117 SNe Ia observed by the Nearby Supernova Factory, as well as the Union2 compilation of SN Ia data already in the literature.

Methods. The bulk flow velocity was determined from SN data binned in redshift shells by including a coherent motion (dipole) in a cosmological fit. Additionally, a method of spatially smoothing the Hubble residuals was used to verify the results of the dipole fit. To constrain the location and mass of a potential mass concentration (e.g., the Shapley supercluster) responsible for the peculiar motion, we fit a Hubble law modified by adding an additional mass concentration.

Results. The analysis shows a bulk flow that is consistent with the direction of the CMB dipole up to z ~ 0.06, thereby doubling the volume over which conventional distance measures are sensitive to a bulk flow. We see no significant turnover behind the center of the Shapley supercluster. A simple attractor model in the proximity of the Shapley supercluster is only marginally consistent with our data, suggesting the need for another, more distant source. In the redshift shell 0.06 < z < 0.1, we constrain the bulk flow velocity to ≤240 km s^-1 (68% confidence level) for the direction of the CMB dipole, in contradiction to recent claims of the existence of a large-amplitude dark flow.