26 research outputs found
Cluster Cepheids with High Precision Gaia Parallaxes, Low Zeropoint Uncertainties, and Hubble Space Telescope Photometry
We present HST photometry of 17 Cepheids in open clusters and their mean
parallaxes from Gaia EDR3. These parallaxes are more precise than those from
individual Cepheids (G<8 mag) previously used to measure the Hubble constant
because they are derived from an average of >300 stars per cluster. Cluster
parallaxes also have smaller systematic uncertainty because their stars lie in
the range (G>13 mag) where the Gaia parallax calibration is most comprehensive.
Cepheid photometry employed in the period--luminosity relation was measured
using the same instrument(WFC3) and filters(F555W,F814W,F160W) as extragalactic
Cepheids in SNIa hosts. We find no evidence of residual parallax offset in this
magnitude range, zp=-3+/-4 muas, consistent with Lindegren:2021b and most
studies. The Cepheid luminosity (P=10d, solar-metallicity) in the HST
near-infrared, Wesenheit system derived from the cluster sample is
M_{H,1}^W=-5.902+/-0.025 and -5.890+/-0.018 mag with or without simultaneous
determination of a parallax offset, respectively. These results are similar to
measurements from field Cepheids, confirming the accuracy of the Gaia
parallaxes over a broad range of magnitudes. The SH0ES distance ladder
calibrated solely from this sample gives H_0=72.8+/-1.3 and H_0=73.2+/-1.1
km/s/Mpc with or without offset marginalization; combined with all anchors we
find H_0=73.01+/-0.99 and 73.15+/-0.97, respectively, a 5% or 7% reduction in
the uncertainty and a 5.3 sigma Hubble Tension relative to Planck+LambdaCDM. It
appears increasingly difficult to reconcile two of the best measured cosmic
scales, parallaxes from Gaia and the angular size of the acoustic scale of the
CMB, using the simplest form of LambdaCDM to join the two.Comment: 12 pages, submitted to ApJ, comments welcom
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
Type Ia Supernova Distances at z > 1.5 from the Hubble Space Telescope Multi-Cycle Treasury Programs: The Early Expansion Rate
We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z > 1 (9
at 1.5 < z < 2.3) recently discovered in the CANDELS and CLASH Multi-Cycle
Treasury programs using WFC3 on the Hubble Space Telescope. We combine these
SNe Ia with a new compilation of 1050 SNe Ia, jointly calibrated and corrected
for simulated survey biases to produce accurate distance measurements. We
present unbiased constraints on the expansion rate at six redshifts in the
range 0.07 < z < 1.5 based only on this combined SN Ia sample. The added
leverage of our new sample at z > 1.5 leads to a factor of ~3 improvement in
the determination of the expansion rate at z = 1.5, reducing its uncertainty to
~20%, a measurement of H(z=1.5)/H0=2.67 (+0.83,-0.52). We then demonstrate that
these six measurements alone provide a nearly identical characterization of
dark energy as the full SN sample, making them an efficient compression of the
SN Ia data. The new sample of SNe Ia at z > 1 usefully distinguishes between
alternative cosmological models and unmodeled evolution of the SN Ia distance
indicators, placing empirical limits on the latter. Finally, employing a
realistic simulation of a potential WFIRST SN survey observing strategy, we
forecast optimistic future constraints on the expansion rate from SNe Ia.Comment: 14 pages, 5 figures, 7 tables; submitted to Ap
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
Photometric Classification of 2315 Pan-STARRS1 Supernovae with Superphot
The classification of supernovae (SNe) and its impact on our understanding of explosion physics and progenitors have traditionally been based on the presence or absence of certain spectral features. However, current and upcoming wide-field time-domain surveys have increased the transient discovery rate far beyond our capacity to obtain even a single spectrum of each new event. We must therefore rely heavily on photometric classification— connecting SN light curves back to their spectroscopically defined classes. Here, we present Superphot, an opensource Python implementation of the machine-learning classification algorithm of Villar et al., and apply it to 2315 previously unclassified transients from the Pan-STARRS1 Medium Deep Survey for which we obtained spectroscopic host-galaxy redshifts. Our classifier achieves an overall accuracy of 82%, with completenesses and purities of >80% for the best classes (SNe Ia and superluminous SNe). For the worst performing SN class (SNe Ibc), the completeness and purity fall to 37% and 21%, respectively. Our classifier provides 1257 newly classified SNe Ia, 521 SNe II, 298 SNe Ibc, 181 SNe IIn, and 58 SLSNe. These are among the largest uniformly observed samples of SNe available in the literature and will enable a wide range of statistical studies of each class
Cosmological Synergies Enabled by Joint Analysis of Multi-probe data from WFIRST, Euclid, and LSST
WFIRST, Euclid, and LSST are all missions designed to perform dedicated cosmology surveys that offer unprecedented statistical constraining power and control of systematic uncertainties. There is a growing realization that these missions will be significantly more powerful when the data are processed and analyzed in unison