5 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 Gravity Collective: A Search for the Electromagnetic Counterpart to the Neutron Star-Black Hole Merger GW190814
We present optical follow-up imaging obtained with the Katzman Automatic
Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel
Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo
gravitational wave (GW) signal from the neutron star-black hole (NSBH) merger
GW190814. We searched the GW190814 localization region (19 deg for the
90th percentile best localization), covering a total of 51 deg and 94.6%
of the two-dimensional localization region. Analyzing the properties of 189
transients that we consider as candidate counterparts to the NSBH merger,
including their localizations, discovery times from merger, optical spectra,
likely host-galaxy redshifts, and photometric evolution, we conclude that none
of these objects are likely to be associated with GW190814. Based on this
finding, we consider the likely optical properties of an electromagnetic
counterpart to GW190814, including possible kilonovae and short gamma-ray burst
afterglows. Using the joint limits from our follow-up imaging, we conclude that
a counterpart with an -band decline rate of 0.68 mag day, similar to
the kilonova AT 2017gfo, could peak at an absolute magnitude of at most
mag (50% confidence). Our data are not constraining for ''red'' kilonovae and
rule out ''blue'' kilonovae with (30% confidence). We
strongly rule out all known types of short gamma-ray burst afterglows with
viewing angles 17 assuming an initial jet opening angle of
and explosion energies and circumburst densities similar to
afterglows explored in the literature. Finally, we explore the possibility that
GW190814 merged in the disk of an active galactic nucleus, of which we find
four in the localization region, but we do not find any candidate counterparts
among these sources.Comment: 86 pages, 9 figure