223 research outputs found
Investigating reciprocity failure in 1.7-micron cut-off HgCdTe detectors
Flux dependent non-linearity (reciprocity failure) in HgCdTe NIR detectors
with 1.7 micron cut-off was investigated. A dedicated test station was designed
and built to measure reciprocity failure over the full dynamic range of near
infrared detectors. For flux levels between 1 and 100,000 photons/sec a
limiting sensitivity to reciprocity failure of 0.3%/decade was achieved. First
measurements on several engineering grade 1.7 micron cut-off HgCdTe detectors
show a wide range of reciprocity failure, from less than 0.5%/decade to about
10%/decade. For at least two of the tested detectors, significant spatial
variation in the effect was observed. No indication for wavelength dependency
was found. The origin of reciprocity failure is currently not well understood.
In this paper we present details of our experimental set-up and show the
results of measurements for several detectors.Comment: 11 pages, 10 figures, to appear in " Astronomical Telescopes and
Instrumentation: High Energy, Optical, and Infrared Detectors for Astronomy
IV", Proceedings of SPIE Vol. 774
Near-Infrared Instrumentation and Millimeter-Wave Simulations For Cosmological Surveys.
The evolution of the Universe is well characterized by the concordance lCDM cosmological model where structure formation is seeded by cold dark matter and accelerated expansion is driven by the cosmological constant. Understanding the history and fate of the Universe requires precise measurements of cosmological parameters. Finding them inconsistent may lead to a more fundamental physical theory. I explore observable probes of cosmological parameters as well as instrumental effects that may obfuscate them.
I develop a framework for simulating millimeter-wave skies including galaxy clusters' Sunyaev-Zel'dovich (SZ) signature. This framework includes astrophysical and instrumental effects. Its primary use is in testing systematic effects resulting from joining intrinsic profile variations and mass dependencies with observational uncertainties and signal extraction techniques as well as multi-wavelength studies. I demonstrate that the signal recovered using Matched Filter is very sensitive to (SZ) profile shapes and potentially leads to biases.
I then consider the impact of galaxy cluster selection and characterization in the maxBCG cluster catalog on recovering a stacked SZ signal in light of recently measured biases. I find that accounting for the mass calibration uncertainty and mis-centering of galaxy clusters may explain the majority of the observed discrepancy. In addition, contrary to others' findings, I conclude that the X-ray sub-sample of maxBCG clusters is similarly affected. My findings suggest that the SZ signal can indeed serve as an alternate mass calibration technique.
I finally focus on instrumental effects in near-infrared (NIR) detectors designed for large surveys of the cosmos. I first characterize the flux dependent non-linearity known as reciprocity failure and find that it can be as large as 10% per decade in flux change but is suppressed by cooling the detectors. I then thoroughly study the quantum efficiency (QE) of a single NIR device under different environmental and illumination conditions and conclude that it can vary significantly. Careful accounting of various sources of uncertainty suggests that some observers may be too confident in the quality of their QE measurements.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102326/1/tomaszbi_1.pd
Measurement of Reciprocity Failure in Near Infrared Detectors
Flux dependent non-linearity (reciprocity failure) in HgCdTe near infrared
detectors can severely impact an instrument's performance, in particular with
respect to precision photometric measurements. The cause of this effect is
presently not understood. To investigate reciprocity failure, a dedicated test
system was built. For flux levels between 1 and 50,000 photons/s, a sensitivity
to reciprocity failure of approximately 0.1%/decade was achieved. A wavelength
independent non-linearity due to reciprocity failure of about 0.35%/decade was
measured in a 1.7 micron HgCdTe detector.Comment: 7 pages, 8 figure
Impact of Systematics on SZ-Optical Scaling Relations
One of the central goals of multi-wavelength galaxy cluster cosmology is to
unite all cluster observables to form a consistent understanding of cluster
mass. Here, we study the impact of systematic effects from optical cluster
catalogs on stacked SZ signals. We show that the optically predicted
Y-decrement can vary by as much as 50% based on the current 2 sigma systematic
uncertainties in the observed mass-richness relationship. Mis-centering and
impurities will suppress the SZ signal compared to expectations for a clean and
perfectly centered optical sample, but to a lesser degree. We show that the
level of these variations and suppression is dependent on the amount of
systematics in the optical cluster catalogs. We also study X-ray
luminosity-dependent sub-sampling of the optical catalog and find that it
creates Malmquist bias increasing the observed Y-decrement of the stacked
signal. We show that the current Planck measurements of the Y-decrement around
SDSS optical clusters and their X-ray counterparts are consistent with
expectations after accounting for the 1 sigma optical systematic uncertainties
using the Johnston mass richness relation.Comment: 6 pages, 4 figures. Revised to match version accepted in the
Astrophysical Journa
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure
Orientation bias of optically selected galaxy clusters and its impact on stacked weak-lensing analyses
Weak-lensing measurements of the averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. In this paper, we test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues created from N-body simulations populated realistically with galaxies, we ran a suite of optical cluster finders and estimated their optical richness. We binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellipticity of these stacks. We find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the line of sight. We show that weak-lensing alone cannot measure the size of this orientation bias. Weak-lensing masses of stacked optically selected clusters are overestimated by up to 3–6 per cent when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the Dark Energy Survey, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted Sunyaev–Zel’dovich signal of optically selected clusters
A Measurement of the Correlation of Galaxy Surveys with CMB Lensing Convergence Maps from the South Pole Telescope
We compare cosmic microwave background lensing convergence maps derived from South Pole Telescope (SPT) data with galaxy survey data from the Blanco Cosmology Survey, WISE, and a new large Spitzer/IRAC field designed to overlap with the SPT survey. Using optical and infrared catalogs covering between 17 and 68 deg^2 of sky, we detect a correlation between the SPT convergence maps and each of the galaxy density maps at >4σ, with zero correlation robustly ruled out in all cases. The amplitude and shape of the cross-power spectra are in good agreement with theoretical expectations and the measured galaxy bias is consistent with previous work. The detections reported here utilize a small fraction of the full 2500 deg^2 SPT survey data and serve as both a proof of principle of the technique and an illustration of the potential of this emerging cosmological probe
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Projected sensitivity of the LUX-ZEPLIN experiment to the 0νββ decay of Xe 136
The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double β decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to Xe136 neutrinoless double β decay, taking advantage of the significant (>600 kg) Xe136 mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of Xe136 is projected to be 1.06×1026 years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with Xe136 at 1.06×1027 years
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Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment
LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4×10-48 cm2 for a 40 GeV/c2 mass WIMP. Additionally, a 5σ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3×10-43 cm2 (7.1×10-42 cm2) for a 40 GeV/c2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020
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