7,055 research outputs found
Unbiased Cosmological Parameter Estimation from Emission Line Surveys with Interlopers
The galaxy catalogs generated from low-resolution emission line surveys often
contain both foreground and background interlopers due to line
misidentification, which can bias the cosmological parameter estimation. In
this paper, we present a method for correcting the interloper bias by using the
joint-analysis of auto- and cross-power spectra of the main and the interloper
samples. In particular, we can measure the interloper fractions from the
cross-correlation between the interlopers and survey galaxies, because the true
cross-correlation must be negligibly small. The estimated interloper fractions,
in turn, remove the interloper bias in the cosmological parameter estimation.
For example, in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)
low-redshift () [O II] {\AA} emitters contaminate
high-redshift () Lyman- line emitters. We demonstrate that
the joint-analysis method yields a high signal-to-noise ratio measurement of
the interloper fractions while only marginally increasing the uncertainties in
the cosmological parameters relative to the case without interlopers. We also
show the same is true for the high-latitude spectroscopic survey of Wide-Field
Infrared Survey Telescope (WFIRST) mission where contamination occurs between
the Balmer- line emitters at lower redshifts () and Oxygen
([O III] {\AA}) line emitters at higher redshifts ().Comment: 36 pages, 26 figure
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
Generating artificial light curves: Revisited and updated
The production of artificial light curves with known statistical and
variability properties is of great importance in astrophysics. Consolidating
the confidence levels during cross-correlation studies, understanding the
artefacts induced by sampling irregularities, establishing detection limits for
future observatories are just some of the applications of simulated data sets.
Currently, the widely used methodology of amplitude and phase randomisation is
able to produce artificial light curves which have a given underlying power
spectral density (PSD) but which are strictly Gaussian distributed. This
restriction is a significant limitation, since the majority of the light curves
e.g. active galactic nuclei, X-ray binaries, gamma-ray bursts show strong
deviations from Gaussianity exhibiting `burst-like' events in their light
curves yielding long-tailed probability distribution functions (PDFs). In this
study we propose a simple method which is able to precisely reproduce light
curves which match both the PSD and the PDF of either an observed light curve
or a theoretical model. The PDF can be representative of either the parent
distribution or the actual distribution of the observed data, depending on the
study to be conducted for a given source. The final artificial light curves
contain all of the statistical and variability properties of the observed
source or theoretical model i.e. same PDF and PSD, respectively. Within the
framework of Reproducible Research, the code, together with the illustrative
example used in this manuscript, are both made publicly available in the form
of an interactive Mathematica notebook.Comment: Accepted for publication in MNRAS. The paper is 23 pages long and
contains 21 figures and 2 tables. The Mathematica notebook can be found in
the web as part of this paper (Online Material) or at
http://www.astro.soton.ac.uk/~de1e08/ArtificialLightCurves
Probing cosmology and gravity with redshift-space distortions around voids
Cosmic voids in the large-scale structure of the Universe affect the peculiar
motions of objects in their vicinity. Although these motions are difficult to
observe directly, the clustering pattern of their surrounding tracers in
redshift space is influenced in a unique way. This allows to investigate the
interplay between densities and velocities around voids, which is solely
dictated by the laws of gravity. With the help of -body simulations and
derived mock-galaxy catalogs we calculate the average density fluctuations
around voids identified with a watershed algorithm in redshift space and
compare the results with the expectation from general relativity and the
CDM model. We find linear theory to work remarkably well in describing
the dynamics of voids. Adopting a Bayesian inference framework, we explore the
full posterior of our model parameters and forecast the achievable accuracy on
measurements of the growth rate of structure and the geometric distortion
through the Alcock-Paczynski effect. Systematic errors in the latter are
reduced from to when peculiar velocities are taken into
account. The relative parameter uncertainties in galaxy surveys with number
densities comparable to the SDSS MAIN (CMASS) sample probing a volume of
yield () and
(), respectively. At this level of precision
the linear-theory model becomes systematics dominated, with parameter biases
that fall beyond these values. Nevertheless, the presented method is highly
model independent; its viability lies in the underlying assumption of
statistical isotropy of the Universe.Comment: 38 pages, 14 figures. Published in JCAP. Referee comments
incorporated, typos corrected, references added. Considerably improved
results thanks to consideration of full covariance matrix in the MCMC
analysi
- …