Open AccessConstraints on cosmological anisotropy out to z = 1 from Type Ia supernovae
Author(s) -
Kolatt Tsafrir S.,
Lahav Ofer
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04262.x
Subject(s) - physics , astrophysics , redshift , supernova , cosmology , cosmological constant , hubble's law , metric expansion of space , universe , sky , type (biology) , dark energy , theoretical physics , galaxy , ecology , biology
A combined sample of 79 high‐ and low‐redshift Type Ia supernovae (SNe) is used to set constraints on the degree of anisotropy in the Universe out to z≃1. First, we derive the global most probable values of matter density Ω M , the cosmological constant Ω Λ and the Hubble constant H 0 , and find them to be consistent with the published results from the two data sets of Riess et al. and Perlmutter et al. We then examine the Hubble diagram (HD, i.e., the luminosity–redshift relation) in different directions on the sky by utilizing spherical harmonic expansion. In particular, via the analysis of the dipole anisotropy, we divide the sky into the two hemispheres that yield the most discrepant of the three cosmological parameters, and the scatter χ HD 2 in each case. The most discrepant values roughly move along the locus −4Ω M +3Ω Λ =1 (cf. Perlmutter et al.), but by no more than Δ≈2.5 along this line. For a perfect Friedmann–Robertson–Walker universe, Monte Carlo realizations that mimic the current set of SNe yield values higher than the measured Δ in ∼1/5 of the cases (for Ω M ). We discuss implications for the validity of the Cosmological Principle, and possible calibration problems in the SNe data sets.