446 research outputs found
The Impact of Dust on Cepheid and Type Ia Supernova Distances
Milky-Way and intergalactic dust extinction and reddening must be accounted
for in measurements of distances throughout the universe. This work provides a
comprehensive review of the various impacts of cosmic dust focusing
specifically on its effects on two key distance indicators used in the distance
ladder: Cepheid variable stars and Type Ia supernovae. We review the formalism
used for computing and accounting for dust extinction and reddening as a
function of wavelength. We also detail the current state of the art knowledge
of dust properties in the Milky Way and in host galaxies. We discuss how dust
has been accounted for in both the Cepheid and SN distance measurements.
Finally, we show how current uncertainties on dust modeling impact the inferred
luminosities and distances, but that measurements of the Hubble constant remain
robust to these uncertainties.Comment: Invited chapter for the edited book {\it Hubble Constant Tension}
(Eds. E. Di Valentino and D. Brout, Springer Singapore, expected in 2024
A test of Gaia Data Release 1 parallaxes: implications for the local distance scale
We present a comparison of Gaia Data Release 1 (DR1) parallaxes with
photometric parallaxes for a sample of 212 Galactic Cepheids at a median
distance of 2~kpc, and explore their implications on the distance scale and the
local value of the Hubble constant H_0. The Cepheid distances are estimated
from a recent calibration of the near-infrared Period-Luminosity P-L relation.
The comparison is carried out in parallax space, where the DR1 parallax errors,
with a median value of half the median parallax, are expected to be
well-behaved. With the exception of one outlier, the DR1 parallaxes are in
remarkably good global agreement with the predictions, and the published errors
may be conservatively overestimated by about 20%. The parallaxes of 9 Cepheids
brighter than G = 6 may be systematically underestimated, trigonometric
parallaxes measured with the HST FGS for three of these objects confirm this
trend. If interpreted as an independent calibration of the Cepheid luminosities
and assumed to be otherwise free of systematic uncertainties, DR1 parallaxes
would imply a decrease of 0.3% in the current estimate of the local Hubble
constant, well within their statistical uncertainty, and corresponding to a
value 2.5 sigma (3.5 sigma if the errors are scaled) higher than the value
inferred from Planck CMB data used in conjunction with Lambda-CDM. We also test
for a zeropoint error in Gaia parallaxes and find none to a precision of ~20
muas. We caution however that with this early release, the complete systematic
properties of the measurements may not be fully understood at the statistical
level of the Cepheid sample mean, a level an order of magnitude below the
individual uncertainties. The early results from DR1 demonstrate again the
enormous impact that the full mission will likely have on fundamental questions
in astrophysics and cosmology.Comment: A&A, submitted, 6 pages, 3 figure
Type Ia Supernova Distances at Redshift >1.5 from the Hubble Space Telescope Multicycle Treasury Programs: The Early Expansion Rate
We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z γ 1 (9 at 1.5 γ z γ 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 γ z γ 1.5 based only on this combined SN Ia sample. The added leverage of our new sample at z γ 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)/H_0 = 2.69_(-0.52)^(+0.86). We then demonstrate that these six derived expansion rate 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 γ 1.5 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 Wide-Field Infrared Survey Telescope SN survey observing strategy, we forecast optimistic future constraints on the expansion rate from SNe Ia
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