Supernovae as cosmological probes

Nielsen, Jeppe Trøst

doi:10.48550/arxiv.1508.07850

Cited by 1 publication

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“…The largest public catalogues of SNe Ia lightcurves, the JLA [25] and its successor Pantheon [26], employ the 'Spectral Adaptive Lightcurve Template 2' (SALT2) to fit each SNe Ia light curve with 3 parameters: the apparent magnitude m * B (at maximum in the rest frame 'B-band') and the 'shape' and 'colour' corrections, x 1 and c [53] (a 'host galaxy mass correction' may also be included, however the MLE is insensitive to this parameter [44]). The distance modulus is then…”

Section: Data Availability Statementmentioning

confidence: 99%

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Cosmological Inference from within the Peculiar Local Universe

Mohayaee,

Rameez,

Sarkar

2024

Universe

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The existence of ‘peculiar’ velocities due to the formation of cosmic structure marks a point of discord between the real universe and the usually assumed Friedmann–Lemaítre–Robertson–Walker metric, which accomodates only the smooth Hubble expansion on large scales. In the standard ΛCDM model framework, Type Ia supernovae data are routinely “corrected” for the peculiar velocities of both the observer and the supernova host galaxies relative to the cosmic rest frame, in order to infer evidence for acceleration of the expansion rate from their Hubble diagram. However, observations indicate a strong, coherent local bulk flow that continues outward without decaying out to a redshift z≳0.1, contrary to the ΛCDM expectation. By querying the halo catalogue of the Dark Sky Hubble-volume N-body simulation, we find that an observer placed in an unusual environment like our local universe should see correlations between supernovae in the JLA catalogue that are 2–8 times stronger than seen by a typical or Copernican observer. This accounts for our finding that peculiar velocity corrections have a large impact on the value of the cosmological constant inferred from supernova data. We also demonstrate that local universe-like observers will infer a downward biased value of the clustering parameter S8 from comparing the density and velocity fields. More realistic modelling of the peculiar local universe is thus essential for correctly interpreting cosmological data.

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Section: Data Availability Statementmentioning

confidence: 99%

“…Table 1. Best-fit parameters and results for the fits described in Section 2.3 using the Maximum Likelihood Estimator [44]. Including the bulk flow improves the quality of the fit and decreases the significance of accelerated expansion, as seen from the decrease of −2 log L max .…”

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confidence: 99%