7 research outputs found
Leveraging SN Ia spectroscopic similarity to improve the measurement of
Recent studies suggest spectroscopic differences explain a fraction of the
variation in Type Ia supernova (SN Ia) luminosities after light-curve/color
standardization. In this work, (i) we empirically characterize the variations
of standardized SN Ia luminosities, and (ii) we use a spectroscopically
inferred parameter, SIP, to improve the precision of SNe Ia along the distance
ladder and the determination of the Hubble constant (). First, we show
that the \texttt{Pantheon+} covariance model modestly overestimates the
uncertainty of standardized magnitudes by %, in the parameter space
used by the Team to measure ; accounting for this alone
yields km s Mpc. Furthermore, accounting
for spectroscopic similarity between SNe~Ia on the distance ladder reduces
their relative scatter to mag per object (compared to
mag previously). Combining these two findings in the model of SN covariance, we
find an overall 14% reduction (to km s Mpc) of the
uncertainty in the Hubble constant and a modest increase in its value.
Including a budget for systematic uncertainties itemized by Riess et al.
(2022a), we report an updated local Hubble constant with %
uncertainty, km s Mpc. We conclude that
spectroscopic differences among photometrically standardized SNe Ia do not
explain the ``Hubble tension." Rather, accounting for such differences
increases its significance, as the discrepancy against CDM calibrated
by the 2018 measurement rises to 5.7.Comment: 28 pages, 15 figures, accepted to JCA
A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
We report observations from HST of Cepheids in the hosts of 42 SNe Ia used to
calibrate the Hubble constant (H0). These include all suitable SNe Ia in the
last 40 years at z1000 orbits, more than doubling the
sample whose size limits the precision of H0. The Cepheids are calibrated
geometrically from Gaia EDR3 parallaxes, masers in N4258 (here tripling that
Cepheid sample), and DEBs in the LMC. The Cepheids were measured with the same
WFC3 instrument and filters (F555W, F814W, F160W) to negate zeropoint errors.
We present multiple verifications of Cepheid photometry and tests of
background determinations that show measurements are accurate in the presence
of crowding. The SNe calibrate the mag-z relation from the new Pantheon+
compilation, accounting here for covariance between all SN data, with host
properties and SN surveys matched to negate differences. We decrease the
uncertainty in H0 to 1 km/s/Mpc with systematics. We present a comprehensive
set of ~70 analysis variants to explore the sensitivity of H0 to selections of
anchors, SN surveys, z range, variations in the analysis of dust, metallicity,
form of the P-L relation, SN color, flows, sample bifurcations, and
simultaneous measurement of H(z).
Our baseline result from the Cepheid-SN sample is H0=73.04+-1.04 km/s/Mpc,
which includes systematics and lies near the median of all analysis variants.
We demonstrate consistency with measures from HST of the TRGB between SN hosts
and NGC 4258 with Cepheids and together these yield 72.53+-0.99. Including
high-z SN Ia we find H0=73.30+-1.04 with q0=-0.51+-0.024. We find a 5-sigma
difference with H0 predicted by Planck+LCDM, with no indication this arises
from measurement errors or analysis variations considered to date. The source
of this now long-standing discrepancy between direct and cosmological routes to
determining the Hubble constant remains unknown.Comment: 67 pages, 31 figures, replaced to match ApJ accepted version (March
2022), Table 6 distances included here, long form of photometry tables,
fitting code, compact form of data, available from Github page,
https://pantheonplussh0es.github.i
The Pantheon+ Analysis: Evaluating Peculiar Velocity Corrections in Cosmological Analyses with Nearby Type Ia Supernovae
Separating the components of redshift due to expansion and peculiar motion in the nearby universe () is critical for using Type Ia Supernovae (SNe Ia) to measure the Hubble constant () and the equation-of-state parameter of dark energy (). Here, we study the two dominant 'motions' contributing to nearby peculiar velocities: large-scale, coherent-flow (CF) motions and small-scale motions due to gravitationally associated galaxies deemed to be in a galaxy group. We use a set of 584 low- SNe from the Pantheon+ sample, and evaluate the efficacy of corrections to these motions by measuring the improvement of SN distance residuals. We study multiple methods for modeling the large and small-scale motions and show that, while group assignments and CF corrections individually contribute to small improvements in Hubble residual scatter, the greatest improvement comes from the combination of the two (relative standard deviation of the Hubble residuals, Rel. SD, improves from 0.167 to 0.157 mag). We find the optimal flow corrections derived from various local density maps significantly reduce Hubble residuals while raising by km s Mpc as compared to using CMB redshifts, disfavoring the hypothesis that unrecognized local structure could resolve the Hubble tension. We estimate that the systematic uncertainties in cosmological parameters after optimally correcting redshifts are 0.06-0.11 km s Mpc in and 0.02-0.03 in which are smaller than the statistical uncertainties for these measurements: 1.5 km s Mpc for and 0.04 for
The Pantheon+ Analysis: Cosmological Constraints
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from to 2.26. This work features an increased sample size, increased redshift span, and improved treatment of systematic uncertainties in comparison to the original Pantheon analysis and results in a factor of two improvement in cosmological constraining power. For a FlatCDM model, we find from SNe Ia alone. For a FlatCDM model, we measure from SNe Ia alone, H km s Mpc when including the Cepheid host distances and covariance (SH0ES), and when combining the SN likelihood with constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a FlatCDM universe, and measure from Pantheon+ alone, H km s Mpc when including SH0ES, and when combining Pantheon+ with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one third of the total uncertainty in the measurement of H and cannot explain the present "Hubble tension" between local measurements and early-Universe predictions from the cosmological model
The Pantheon+ Analysis: Cosmological Constraints
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from to 2.26. This work features an increased sample size, increased redshift span, and improved treatment of systematic uncertainties in comparison to the original Pantheon analysis and results in a factor of two improvement in cosmological constraining power. For a FlatCDM model, we find from SNe Ia alone. For a FlatCDM model, we measure from SNe Ia alone, H km s Mpc when including the Cepheid host distances and covariance (SH0ES), and when combining the SN likelihood with constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a FlatCDM universe, and measure from Pantheon+ alone, H km s Mpc when including SH0ES, and when combining Pantheon+ with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one third of the total uncertainty in the measurement of H and cannot explain the present "Hubble tension" between local measurements and early-Universe predictions from the cosmological model