517 research outputs found
Measuring galaxy [OII] emission line doublet with future ground-based wide-field spectroscopic surveys
The next generation of wide-field spectroscopic redshift surveys will map the
large-scale galaxy distribution in the redshift range 0.7< z<2 to measure
baryonic acoustic oscillations (BAO). The primary optical signature used in
this redshift range comes from the [OII] emission line doublet, which provides
a unique redshift identification that can minimize confusion with other single
emission lines. To derive the required spectrograph resolution for these
redshift surveys, we simulate observations of the [OII] (3727,3729) doublet for
various instrument resolutions, and line velocities. We foresee two strategies
about the choice of the resolution for future spectrographs for BAO surveys.
For bright [OII] emitter surveys ([OII] flux ~30.10^{-17} erg /cm2/s like
SDSS-IV/eBOSS), a resolution of R~3300 allows the separation of 90 percent of
the doublets. The impact of the sky lines on the completeness in redshift is
less than 6 percent. For faint [OII] emitter surveys ([OII] flux ~10.10^{-17}
erg /cm2/s like DESi), the detection improves continuously with resolution, so
we recommend the highest possible resolution, the limit being given by the
number of pixels (4k by 4k) on the detector and the number of spectroscopic
channels (2 or 3).Comment: 5 pages, 1 figur
The Extended Baryon Oscillation Spectroscopic Survey: Variability Selection and Quasar Luminosity Function
The SDSS-IV/eBOSS has an extensive quasar program that combines several
selection methods. Among these, the photometric variability technique provides
highly uniform samples, unaffected by the redshift bias of traditional
optical-color selections, when quasars cross the stellar locus
or when host galaxy light affects quasar colors at . Here, we present
the variability selection of quasars in eBOSS, focusing on a specific program
that led to a sample of 13,876 quasars to over a 94.5
deg region in Stripe 82, an areal density 1.5 times higher than over the
rest of the eBOSS footprint. We use these variability-selected data to provide
a new measurement of the quasar luminosity function (QLF) in the redshift range
. Our sample is denser, reaches deeper than those used in previous
studies of the QLF, and is among the largest ones. At the faint end, our QLF
extends to at low redshift and to
at . We fit the QLF using two independent double-power-law models with
ten free parameters each. The first model is a pure luminosity-function
evolution (PLE) with bright-end and faint-end slopes allowed to be different on
either side of . The other is a simple PLE at , combined with a
model that comprises both luminosity and density evolution (LEDE) at .
Both models are constrained to be continuous at . They present a
flattening of the bright-end slope at large redshift. The LEDE model indicates
a reduction of the break density with increasing redshift, but the evolution of
the break magnitude depends on the parameterization. The models are in
excellent accord, predicting quasar counts that agree within 0.3\% (resp.,
1.1\%) to (resp., ). The models are also in good agreement over
the entire redshift range with models from previous studies.Comment: 15 pages, 12 figures, accepted for publication in A&
Characterizing unknown systematics in large scale structure surveys
Photometric large scale structure (LSS) surveys probe the largest volumes in
the Universe, but are inevitably limited by systematic uncertainties. Imperfect
photometric calibration leads to biases in our measurements of the density
fields of LSS tracers such as galaxies and quasars, and as a result in
cosmological parameter estimation. Earlier studies have proposed using
cross-correlations between different redshift slices or cross-correlations
between different surveys to reduce the effects of such systematics. In this
paper we develop a method to characterize unknown systematics. We demonstrate
that while we do not have sufficient information to correct for unknown
systematics in the data, we can obtain an estimate of their magnitude. We
define a parameter to estimate contamination from unknown systematics using
cross-correlations between different redshift slices and propose discarding
bins in the angular power spectrum that lie outside a certain contamination
tolerance level. We show that this method improves estimates of the bias using
simulated data and further apply it to photometric luminous red galaxies in the
Sloan Digital Sky Survey as a case study.Comment: 24 pages, 6 figures; Expanded discussion of results, added figure 2;
Version to be published in JCA
Magnetic order and spin dynamics in the proximity of a ferromagnetic quantum critical point: A {\mu}SR study of YbNi4P2
The local 4f-electronic spin dynamics and magnetic order in YbNi4P2 were
studied by means of muon-spin relaxation measurements. Zero-field muon-spin
relaxation proves static magnetic order with a strongly reduced ordered Yb3+
moment of (2.5-4.6) \times 10-2{\mu}B, below TC = 140 mK. Above TC, the
muon-spin polarization P(t,B) is dominated by quasihomogeneous spin
fluctuations and exhibits a time-field scaling relation P(t,B) =
P(t/B{\gamma}), indicating cooperative critical spin dynamics in the system. At
T = 190 mK, slightly above TC, {\gamma} = 0.81(5), suggesting time-scale
invariant power-law behavior for the dynamic electronic spin-spin
autocorrelation function.Comment: 5 pages, 4 figure
The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: selecting emission line galaxies using the Fisher discriminant
We present a new selection technique of producing spectroscopic target
catalogues for massive spectroscopic surveys for cosmology. This work was
conducted in the context of the extended Baryon Oscillation Spectroscopic
Survey (eBOSS), which will use ~200 000 emission line galaxies (ELGs) at
0.6<zspec<1.0 to obtain a precise baryon acoustic oscillation measurement. Our
proposed selection technique is based on optical and near-infrared broad-band
filter photometry. We used a training sample to define a quantity, the Fisher
discriminant (linear combination of colours), which correlates best with the
desired properties of the target: redshift and [OII] flux. The proposed
selections are simply done by applying a cut on magnitudes and this Fisher
discriminant. We used public data and dedicated SDSS spectroscopy to quantify
the redshift distribution and [OII] flux of our ELG target selections. We
demonstrate that two of our selections fulfil the initial eBOSS/ELG redshift
requirements: for a target density of 180 deg^2, ~70% of the selected objects
have 0.6<zspec<1.0 and only ~1% of those galaxies in the range 0.6<zspec<1.0
are expected to have a catastrophic zspec estimate. Additionally, the stacked
spectra and stacked deep images for those two selections show characteristic
features of star-forming galaxies. The proposed approach using the Fisher
discriminant could, however, be used to efficiently select other galaxy
populations, based on multi-band photometry, providing that spectroscopic
information is available. This technique could thus be useful for other future
massive spectroscopic surveys such as PFS, DESI, and 4MOST.Comment: Version published in A&
A Simple Likelihood Method for Quasar Target Selection
We present a new method for quasar target selection using photometric fluxes
and a Bayesian probabilistic approach. For our purposes we target quasars using
Sloan Digital Sky Survey (SDSS) photometry to a magnitude limit of g=22. The
efficiency and completeness of this technique is measured using the Baryon
Oscillation Spectroscopic Survey (BOSS) data, taken in 2010. This technique was
used for the uniformly selected (CORE) sample of targets in BOSS year one
spectroscopy to be realized in the 9th SDSS data release. When targeting at a
density of 40 objects per sq-deg (the BOSS quasar targeting density) the
efficiency of this technique in recovering z>2.2 quasars is 40%. The
completeness compared to all quasars identified in BOSS data is 65%. This paper
also describes possible extensions and improvements for this techniqueComment: Updated to accepted version for publication in the Astrophysical
Journal. 10 pages, 10 figures, 3 table
On model selection forecasting, Dark Energy and modified gravity
The Fisher matrix approach (Fisher 1935) allows one to calculate in advance
how well a given experiment will be able to estimate model parameters, and has
been an invaluable tool in experimental design. In the same spirit, we present
here a method to predict how well a given experiment can distinguish between
different models, regardless of their parameters. From a Bayesian viewpoint,
this involves computation of the Bayesian evidence. In this paper, we
generalise the Fisher matrix approach from the context of parameter fitting to
that of model testing, and show how the expected evidence can be computed under
the same simplifying assumption of a gaussian likelihood as the Fisher matrix
approach for parameter estimation. With this `Laplace approximation' all that
is needed to compute the expected evidence is the Fisher matrix itself. We
illustrate the method with a study of how well upcoming and planned experiments
should perform at distinguishing between Dark Energy models and modified
gravity theories. In particular we consider the combination of 3D weak lensing,
for which planned and proposed wide-field multi-band imaging surveys will
provide suitable data, and probes of the expansion history of the Universe,
such as proposed supernova and baryonic acoustic oscillations surveys. We find
that proposed large-scale weak lensing surveys from space should be able
readily to distinguish General Relativity from modified gravity models.Comment: 6 pages, 2 figure
Angular clustering properties of the DESI QSO target selection using DR9 Legacy Imaging Surveys
The quasar target selection for the upcoming survey of the Dark Energy Spectroscopic Instrument (DESI) will be fixed for the next 5 yr. The aim of this work is to validate the quasar selection by studying the impact of imaging systematics as well as stellar and galactic contaminants, and to develop a procedure to mitigate them. Density fluctuations of quasar targets are found to be related to photometric properties such as seeing and depth of the Data Release 9 of the DESI Legacy Imaging Surveys. To model this complex relation, we explore machine learning algorithms (random forest and multilayer perceptron) as an alternative to the standard linear regression. Splitting the footprint of the Legacy Imaging Surveys into three regions according to photometric properties, we perform an independent analysis in each region, validating our method using extended Baryon Oscillation Spectroscopic Survey (eBOSS) EZ-mocks. The mitigation procedure is tested by comparing the angular correlation of the corrected target selection on each photometric region to the angular correlation function obtained using quasars from the Sloan Digital Sky Survey (SDSS) Data Release 16. With our procedure, we recover a similar level of correlation between DESI quasar targets and SDSS quasars in two-thirds of the total footprint and we show that the excess of correlation in the remaining area is due to a stellar contamination that should be removed with DESI spectroscopic data. We derive the Limber parameters in our three imaging regions and compare them to previous measurements from SDSS and the 2dF QSO Redshift Survey.This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under contract no. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract no. AST-0950945 to the NSF’s National Optical–Infrared Astronomy Research Laboratory; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology, Mexico; the Ministry of Economy of Spain, and by the DESI Member Institutions.
ADM was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC0019022
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