22 research outputs found
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
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Strong Lens Time Delay Challenge: II. Results of TDC1
We present the results of the first strong lens time delay challenge. The
motivation, experimental design, and entry level challenge are described in a
companion paper. This paper presents the main challenge, TDC1, which consisted
of analyzing thousands of simulated light curves blindly. The observational
properties of the light curves cover the range in quality obtained for current
targeted efforts (e.g.,~COSMOGRAIL) and expected from future synoptic surveys
(e.g.,~LSST), and include simulated systematic errors. \nteamsA\ teams
participated in TDC1, submitting results from \nmethods\ different method
variants. After a describing each method, we compute and analyze basic
statistics measuring accuracy (or bias) , goodness of fit ,
precision , and success rate . For some methods we identify outliers as
an important issue. Other methods show that outliers can be controlled via
visual inspection or conservative quality control. Several methods are
competitive, i.e., give , , and , with some of
the methods already reaching sub-percent accuracy. The fraction of light curves
yielding a time delay measurement is typically in the range 20--40\%. It
depends strongly on the quality of the data: COSMOGRAIL-quality cadence and
light curve lengths yield significantly higher than does sparser sampling.
Taking the results of TDC1 at face value, we estimate that LSST should provide
around 400 robust time-delay measurements, each with and ,
comparable to current lens modeling uncertainties. In terms of observing
strategies, we find that and depend mostly on season length, while P
depends mostly on cadence and campaign duration.Comment: referee's comments incorporated; to appear in Ap