The Pantheon+ Analysis: Improving the Redshifts and Peculiar Velocities of Type Ia Supernovae Used in Cosmological Analyses. (arXiv:2112.01471v1 [astro-ph.CO])

<a href="http://arxiv.org/find/astro-ph/1/au:+Carr_A/0/1/0/all/0/1">Anthony Carr</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Davis_T/0/1/0/all/0/1">Tamara M. Davis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scolnic_D/0/1/0/all/0/1">Daniel Scolnic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Said_K/0/1/0/all/0/1">Khaled Said</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brout_D/0/1/0/all/0/1">Dillon Brout</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peterson_E/0/1/0/all/0/1">Erik R. Peterson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kessler_R/0/1/0/all/0/1">Richard Kessler</a>

We examine the redshifts of a comprehensive set of published Type Ia

supernovae, and provide a combined, improved catalog with updated redshifts. We

improve on the original catalogs by using the most up-to-date heliocentric

redshift data available; ensuring all redshifts have uncertainty estimates;

using the exact formulae to convert heliocentric redshifts into the Cosmic

Microwave Background (CMB) frame; and utilizing an improved peculiar velocity

model that calculates local motions in redshift-space and more realistically

accounts for the external bulk flow at high-redshifts. In total we reviewed

2821 supernova redshifts; 534 are comprised of repeat-observations of the same

supernovae and 1764 pass the cosmology sample quality cuts. We found 5 cases of

missing or incorrect heliocentric corrections, 44 incorrect or missing

supernova coordinates, 230 missing heliocentric or CMB frame redshifts, and

1200 missing redshift uncertainties. Of the 2287 unique Type Ia supernovae in

our sample (1594 of which satisfy cosmology-sample cuts) we updated 990

heliocentric redshifts. The absolute corrections range between $10^{-8} leq

Delta z leq 0.038$, and RMS$(Delta z) sim 3times 10^{-3}$. The sign of the

correction was essentially random, so the mean and median corrections are

small: $4times 10^{-4}$ and $4times 10^{-6}$ respectively. We examine the

impact of these improvements for $H_0$ and the dark energy equation of state

$w$ and find that the cosmological results change by $Delta H_0 = -0.11$ km

s$^{-1}$ Mpc$^{-1}$ and $Delta w = -0.001$, both significantly smaller than

previously reported uncertainties for $H_0$ of 1.4 km s$^{-1}$ Mpc$^{-1}$ and

$w$ of 0.04 respectively.

We examine the redshifts of a comprehensive set of published Type Ia

supernovae, and provide a combined, improved catalog with updated redshifts. We

improve on the original catalogs by using the most up-to-date heliocentric

redshift data available; ensuring all redshifts have uncertainty estimates;

using the exact formulae to convert heliocentric redshifts into the Cosmic

Microwave Background (CMB) frame; and utilizing an improved peculiar velocity

model that calculates local motions in redshift-space and more realistically

accounts for the external bulk flow at high-redshifts. In total we reviewed

2821 supernova redshifts; 534 are comprised of repeat-observations of the same

supernovae and 1764 pass the cosmology sample quality cuts. We found 5 cases of

missing or incorrect heliocentric corrections, 44 incorrect or missing

supernova coordinates, 230 missing heliocentric or CMB frame redshifts, and

1200 missing redshift uncertainties. Of the 2287 unique Type Ia supernovae in

our sample (1594 of which satisfy cosmology-sample cuts) we updated 990

heliocentric redshifts. The absolute corrections range between $10^{-8} leq

Delta z leq 0.038$, and RMS$(Delta z) sim 3times 10^{-3}$. The sign of the

correction was essentially random, so the mean and median corrections are

small: $4times 10^{-4}$ and $4times 10^{-6}$ respectively. We examine the

impact of these improvements for $H_0$ and the dark energy equation of state

$w$ and find that the cosmological results change by $Delta H_0 = -0.11$ km

s$^{-1}$ Mpc$^{-1}$ and $Delta w = -0.001$, both significantly smaller than

previously reported uncertainties for $H_0$ of 1.4 km s$^{-1}$ Mpc$^{-1}$ and

$w$ of 0.04 respectively.

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