Concerns about the reliability of publicly available SNe Ia data. (arXiv:1905.00221v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rameez_M/0/1/0/all/0/1">Mohamed Rameez</a>
I highlight several concerns regarding the consistency of Type Ia supernova
data in the publicly available Pantheon and JLA compilations. The measured
heliocentric redshifts (zhel) of $sim$150 SNe Ia as reported in the Pantheon
catalogue are significantly discrepant from those in JLA – with 58 having
differences amounting to between 5 and 137 times the quoted measurement
uncertainty. The discrepancy seems to have been introduced in the process of
rectifying a previously reported issue. The Pantheon catalogue until very
recently had the redshifts of all SNe Ia up to z $sim$ 0.3 modified under the
guise of ‘peculiar velocity corrections’ – although there is no information on
peculiar velocities at such high redshifts. While this has reportedly been
rectified on Github by removing peculiar velocity corrections for z > 0.08, the
impact of this on the published cosmological analysis of the Pantheon catalogue
is not stated. In JLA, the effect of these ‘corrections’ is to significantly
bias the inferred value of $Omega_{Lambda}$ towards higher values, while the
equivalent effect on Pantheon cannot be ascertained due to the unavailability
of the individual components of the covariance matrix in the public domain. I
provide Jupyter notebooks and URLs in order to allow the reader to ascertain
the veracity of these assertions.
I highlight several concerns regarding the consistency of Type Ia supernova
data in the publicly available Pantheon and JLA compilations. The measured
heliocentric redshifts (zhel) of $sim$150 SNe Ia as reported in the Pantheon
catalogue are significantly discrepant from those in JLA – with 58 having
differences amounting to between 5 and 137 times the quoted measurement
uncertainty. The discrepancy seems to have been introduced in the process of
rectifying a previously reported issue. The Pantheon catalogue until very
recently had the redshifts of all SNe Ia up to z $sim$ 0.3 modified under the
guise of ‘peculiar velocity corrections’ – although there is no information on
peculiar velocities at such high redshifts. While this has reportedly been
rectified on Github by removing peculiar velocity corrections for z > 0.08, the
impact of this on the published cosmological analysis of the Pantheon catalogue
is not stated. In JLA, the effect of these ‘corrections’ is to significantly
bias the inferred value of $Omega_{Lambda}$ towards higher values, while the
equivalent effect on Pantheon cannot be ascertained due to the unavailability
of the individual components of the covariance matrix in the public domain. I
provide Jupyter notebooks and URLs in order to allow the reader to ascertain
the veracity of these assertions.
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