Photometric Performance Research Articles

The PAU Survey: early demonstration of photometric redshift performance in the COSMOS field

The PAU Survey (PAUS) is an innovative photometric survey with 40 narrow bands at the William Herschel Telescope (WHT). The narrow bands are spaced at 100\AA\ intervals covering the range 4500\AA\ to 8500\AA\ and, in combination with standard broad bands, enable excellent redshift precision. This paper describes the technique, galaxy templates and additional photometric calibration used to determine early photometric redshifts from PAUS. Using BCNz2, a new photometric redshift code developed for this purpose, we characterise the photometric redshift performance using PAUS data on the COSMOS field. Comparison to secure spectra from zCOSMOS DR3 shows that PAUS achieves $\sigma_{68} /(1+z) = 0.0037$ to $i_{\mathrm{AB}} < 22.5$ when selecting the best 50% of the sources based on a photometric redshift quality cut. Furthermore, a higher photo-z precision ($\sigma_{68}/(1+z) \sim 0.001$) is obtained for a bright and high quality selection, which is driven by the identification of emission lines. We conclude that PAUS meets its design goals, opening up a hitherto uncharted regime of deep, wide, and dense galaxy survey with precise redshifts that will provide unique insights into the formation, evolution and clustering of galaxies, as well as their intrinsic alignments.

CPz: Classification-aided photometric-redshift estimation

Broadband photometry offers a time and cost effective method to reconstruct the continuum emission of celestial objects. Thus, photometric redshift estimation has supported the scientific exploitation of extragalactic multiwavelength surveys for more than twenty years. Deep fields have been the backbone of galaxy evolution studies and have brought forward a collection of various approaches in determining photometric redshifts. In the era of precision cosmology, with the upcoming Euclid and LSST surveys, very tight constraints are put on the expected performance of photometric redshift estimation using broadband photometry, thus new methods have to be developed in order to reach the required performance. We present a novel automatic method of optimizing photometric redshift performance, the classification-aided photometric redshift estimation (CPz). The main feature of CPz is the unified treatment of all classes of objects detected in extragalactic surveys: galaxies of any type (passive, starforming and starbursts), active galactic nuclei (AGN), quasi-stellar objects (QSO), stars and also includes the identification of potential photometric redshift catastrophic outliers. The method operates in three stages. First, the photometric catalog is confronted with star, galaxy and QSO model templates by means of spectral energy distribution fitting. Second, three machine-learning classifiers are used to identify 1) the probability of each source to be a star, 2) the optimal photometric redshift model library set-up for each source and 3) the probability to be a photometric redshift catastrophic outlier. Lastly, the final sample is assembled by identifying the probability thresholds to be applied on the outcome of each of the three classifiers. Hence, with the final stage we can create a sample appropriate for a given science case, for example favoring purity over completeness. We apply our method to the near-infrared VISTA public surveys, matched with optical photometry from CFHTLS, KIDS and SDSS, mid-infrared WISE photometry and ultra-violet photometry from the Galaxy Evolution Explorer (GALEX). We show that CPz offers improved photometric redshift performance for both normal galaxies and AGN without the need for extra X-ray information.

Color temperature tunable phosphor-coated white LEDs with excellent photometric and colorimetric performances.

The optimization model for the luminous efficacy (LE) of a correlated color temperature (CCT) tunable phosphor-coated white LED (pc-WLED) was developed. The optimal pc-WLEDs with green (498.7nm, 70.0nm), yellow (569.2nm, 83.4nm), and red (638.7nm, 70.0nm) phosphors excited by a blue chip (442.4nm, 35.0nm) could achieve a color fidelity index (Rf) of 97 and LEs of 118-127lm/W at CCTs of 2700-6500K for a radiant efficiency of the blue chip of 60% and a quantum efficiency of a phosphor layer of 90%. Compared to quantum dot WLEDs (QD-WLEDs), the LEs of the optimal pc-WLEDs are lower only by 2.7%-4.8% than the optimal QD-WLEDs at CCTs of 2700-6500K, so that QD-WLEDs have only a slight advantage in terms of luminous efficacy for excellent color rendition. Four real pc-WLEDs with Rfs of 96-97 and LEs of 93-106lm/W at CCTs of 3037K, 4081K, 4951K, and 6443K were demonstrated.

Establishing Functional Model of Photometric Performance of Trichromatic Light Sources in Chromaticity Diagrams

In this study, we conducted a combined examination of the photometric and colorimetric performances of trichromatic light sources, which are synthesized by three kinds of light-source units, by transferring their photometric performance to chromaticity diagrams. Contour maps of three photometric performances, which are within a triangle gamut-area formed by three chromaticity coordinates relating to three-light-source-units of a trichromatic light source, were drawn to include the luminous efficacy of radiation (LER) in photopic, scotopic, and cirtopic vision. Functional models of the three different photometric performances as a function of chromaticity coordinates x and y based on the contour maps have been proposed. The functional models quantify all the photometric characteristics in the gamut area and can predict the performances for different synthesis of trichromatic light sources. Using the proposed model, it is possible to evaluate the present performance of trichromatic light sources and provide a method for optimization. An example of evaluation and optimization of a commercial RGB-LED light source was conducted using this proposed approach. Results show that the randomly chosen optimized points in the best optimization ways in the chromaticity diagram for LERs reach 16%, 31%, and 72% improvement in photopic, scotopic, and cirtopic vision, respectively.

Index for the evaluation of the general photometric performance of photometers

The General V(λ) Mismatch Index, f1', was defined for a general description of the photometric performance of photometers. This index is widely-used in photometry, and it is very relevant for selecting photometers for low-uncertainty photometric measurements. It quantifies the spectral mismatch between the relative spectral responsivity of a photometer and the luminous efficiency function for photopic vision, V(λ). The linear correlation between the real general photometric measurement error and f1' of 77 photometers was studied for four sets of light sources: R, G and B LEDs (narrowband spectral power distributions, SPDs), blackbodies at different colour temperatures (broadband SPDs), phosphor-based LEDs at different correlated color temperatures (SPDs with narrow- and broad-band features), and a mixture of blackbodies and phosphor-based LED sources. This article shows that it can be defined an alternative index which is notably better correlated with the real general photometric measurement error of the photometers under light sources with broadband features in their SPDs, adequate for general lighting. This index is based on filtering the high spectral frequencies variations between the relative spectral responsivity of the photometer and V(λ). The use of this new index for the assessment of the general photometric performance of photometers would improve the selection of high quality photometers and, consequently, would contribute to the general improvement of photometric measurements.

Characterization and photometric performance of the Hyper Suprime-Cam Software Pipeline

Abstract The Subaru Strategic Program (SSP) is an ambitious multi-band survey using the Hyper Suprime-Cam (HSC) on the Subaru telescope. The Wide layer of the SSP is both wide and deep, reaching a detection limit of i ∼ 26.0 mag. At these depths, it is challenging to achieve accurate, unbiased, and consistent photometry across all five bands. The HSC data are reduced using a pipeline that builds on the prototype pipeline for the Large Synoptic Survey Telescope. We have developed a Python-based, flexible framework to inject synthetic galaxies into real HSC images, called SynPipe. Here we explain the design and implementation of SynPipe and generate a sample of synthetic galaxies to examine the photometric performance of the HSC pipeline. For stars, we achieve 1% photometric precision at i ∼ 19.0 mag and 6% precision at i ∼ 25.0 in the i band (corresponding to statistical scatters of ∼0.01 and ∼0.06 mag respectively). For synthetic galaxies with single-Sérsic profiles, forced CModel photometry achieves 13% photometric precision at i ∼ 20.0 mag and 18% precision at i ∼ 25.0 in the i band (corresponding to statistical scatters of ∼0.15 and ∼0.22 mag respectively). We show that both forced point spread function and CModel photometry yield unbiased color estimates that are robust to seeing conditions. We identify several caveats that apply to the version of HSC pipeline used for the first public HSC data release (DR1) that need to be taking into consideration. First, the degree to which an object is blended with other objects impacts the overall photometric performance. This is especially true for point sources. Highly blended objects tend to have larger photometric uncertainties, systematically underestimated fluxes, and slightly biased colors. Secondly, &amp;gt;20% of stars at 22.5 &amp;lt; i &amp;lt; 25.0 mag can be misclassified as extended objects. Thirdly, the current CModel algorithm tends to strongly underestimate the half-light radius and ellipticity of galaxy with i &amp;gt; 21.5 mag.

Photometric redshifts for the next generation of deep radio continuum surveys – I. Template fitting

We present a study of photometric redshift performance for galaxies and active galactic nuclei detected in deep radio continuum surveys. Using two multi-wavelength datasets, over the NOAO Deep Wide Field Survey Bo\"otes and COSMOS fields, we assess photometric redshift (photo-z) performance for a sample of $\sim 4,500$ radio continuum sources with spectroscopic redshifts relative to those of $\sim 63,000$ non radio-detected sources in the same fields. We investigate the performance of three photometric redshift template sets as a function of redshift, radio luminosity and infrared/X-ray properties. We find that no single template library is able to provide the best performance across all subsets of the radio detected population, with variation in the optimum template set both between subsets and between fields. Through a hierarchical Bayesian combination of the photo-z estimates from all three template sets, we are able to produce a consensus photo-z estimate which equals or improves upon the performance of any individual template set.

An optically-selected cluster catalog at redshift 0.1 &amp;lt; z &amp;lt; 1.1 from the Hyper Suprime-Cam Subaru Strategic Program S16A data

Abstract We present an optically-selected cluster catalog from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The HSC images are sufficiently deep to detect cluster member galaxies down to M* ∼ 1010.2 M⊙ even at z ∼ 1, allowing a reliable cluster detection at such high redshifts. We apply the CAMIRA algorithm to the HSC Wide S16A dataset covering ∼232 deg2 to construct a catalog of 1921 clusters at redshift 0.1 &amp;lt; z &amp;lt; 1.1 and richness ${\skew7\hat{N}}_{\rm mem}&amp;gt;15$ that roughly corresponds to M200m ≳ 1014 h−1 M⊙. We confirm good cluster photometric redshift performance, with the bias and the scatter in Δz/(1 + z) being better than 0.005 and 0.01, respectively, over most of the redshift range. We compare our cluster catalog with large X-ray cluster catalogs from the XXL and XMM-LSS (the XMM Large Scale Structure) surveys and find good correlation between richness and X-ray properties.We also study the mis-centering effect from the distribution of offsets between optical and X-ray cluster centers. We confirm the high (&amp;gt;0.9) completeness and purity for high-mass clusters by analyzing mock galaxy catalogs.

Theoretical Modeling of Luminous Efficacy for High-Power White Light-Emitting Diodes**Supported by the National Natural Science Foundation of China under Grant Nos 51307113 and 51407124, and the Natural Science Foundation of Jiangsu Province under Grant No BK20130307.

The photometric characteristics of high-power white light-emitting diode (LED) devices are investigated. A theoretical model for the luminous efficacy of high-power white LED devices and LED systems is proposed. With the proposed theoretical model, the mechanism of the luminous efficacy decrease is explained. Meanwhile, the model can be used to estimate the luminous efficacy of LEDs under general operation conditions, such as different operation temperatures and injection currents. The wide validity of the luminous efficacy model is experimentally verified through the measurements of different types of LEDs. The experimental results demonstrate a high estimation accuracy. The proposed models not only can be applied to estimate the LED photometric performance, but also is helpful for reliability research of LEDs.

GPhoton: THE GALEX PHOTON DATA ARCHIVE

ABSTRACT gPhoton is a new database product and software package that enables analysis of GALEX ultraviolet data at the photon level. The project’s stand-alone, pure-Python calibration pipeline reproduces the functionality of the original mission pipeline to reduce raw spacecraft data to lists of time-tagged, sky-projected photons, which are then hosted in a publicly available database by the Mikulski Archive at Space Telescope. This database contains approximately 130 terabytes of data describing approximately 1.1 trillion sky-projected events with a timestamp resolution of five milliseconds. A handful of Python and command-line modules serve as a front end to interact with the database and to generate calibrated light curves and images from the photon-level data at user-defined temporal and spatial scales. The gPhoton software and source code are in active development and publicly available under a permissive license. We describe the motivation, design, and implementation of the calibration pipeline, database, and tools, with emphasis on divergence from prior work, as well as challenges created by the large data volume. We summarize the astrometric and photometric performance of gPhoton relative to the original mission pipeline. For a brief example of short time-domain science capabilities enabled by gPhoton, we show new flares from the known M-dwarf flare star CR Draconis. The gPhoton software has permanent object identifiers with the ASCL (ascl:1603.004) and DOI (doi:10.17909/T9CC7G). This paper describes the software as of version v1.27.2.

The 2-degree Field Lensing Survey: photometric redshifts from a large new training sample tor &lt; 19.5

We present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2dFLenS project. This training set is located in a 700 sq deg area of the KiDS South field and is randomly selected and nearly complete at r<19.5. We investigate the photometric redshift performance obtained with ugriz photometry from VST-ATLAS and W1/W2 from WISE, based on several empirical and template methods. The best redshift errors are obtained with kernel-density estimation, as are the lowest biases, which are consistent with zero within statistical noise. The 68th percentiles of the redshift scatter for magnitude-limited samples at r<(15.5, 17.5, 19.5) are (0.014, 0.017, 0.028). In this magnitude range, there are no known ambiguities in the colour-redshift map, consistent with a small rate of redshift outliers. In the fainter regime, the KDE method produces p(z) estimates per galaxy that represent unbiased and accurate redshift frequency expectations. The p(z) sum over any subsample is consistent with the true redshift frequency plus Poisson noise. Further improvements in redshift precision at r<20 would mostly be expected from filter sets with narrower passbands to increase the sensitivity of colours to small changes in redshift.

Influence of Driving Current on Photometric Performances of a White Light OLED

In this paper, we demonstrate how driving current affects photometric performances of a white light organic light emitting diode (OLED) for general lighting purpose. Experiments reveal that a ripple current with 40% amplitude, 50-Hz–100-kHz frequency, and sinusoidal and triangle waveform has little influence on the test OLED. In the pulse-width modulation mode, both duty cycle and frequency of pulse current affect OLED's performance, and more particularly, their efficacy and correlated color temperature. Such influences become worse at high frequency and low duty cycle. The reason for this influence is a considerable difference between electron and hole mobility, and a time-dependent distribution of charge carrier within the structure leading to a movement of recombination zone therefrom.

High visibility reflective sign sheeting materials: field and computational evaluations of visual performance

Highway signs provide important information to drivers to assist in navigation, to identify potentially hazardous roadway locations, and to remind drivers of safe operating practices. Ensuring that signs have sufficient visibility to the driving public is a key undertaking by transportation agencies. In order to assist in evaluating and comparing different materials for photometric and visual performance, the present study was undertaken to assess the utility of specifying sign sheeting performance in terms of visual performance. As part of this effort, a practical methodology for conducting field measurements of sign luminance along roadways was developed. In addition to describing the methods for an approach to visual performance based specifications, a spreadsheet tool for calculating minimum sign luminance and visibility from different sign sheeting materials was also developed.

Spectral Optimization of Candle-Like White Light-Emitting Diodes With High Color Rendering Index and Luminous Efficacy

The tradeoff between the color rendering index (CRI) and the luminous efficacy (LE) for candle-like three-hump white light-emitting diodes (LEDs), which consist of blue InGaN chip, yellow aluminate phosphors, and red AlGaInP chip, has been investigated. Spectral models have been separately developed for the optimization process after experimentally measuring spectral power distributions of phosphor materials and semiconductor chips. By filtering billions of defective spectral data with a nonlinear program, optimal values of LE of 272 lm/W and CRI of 96 (CRI No.9 of 98) at a correlated color temperature of 2000 K can be achieved, while LE and CRI are 0.1 lm/W and 83 for candles. These three-humps LEDs are capable of achieving excellent photometric and chromatic performances of candle-like white light. Finally, this study can serve as a critical guide for manufacturing high-CRI candle-like white LEDs.

Scale‐photo‐electro‐thermal model for organic light‐emitting diodes

Organic light-emitting diodes (OLEDs) with large area have a great potential for lighting applications. The knowledge about scale, photometrical, electrical and thermal (SPET) domains of OLEDs is essential to achieve a good performance in lighting systems. This study presents an OLED model based on datasheet information and experimental tests to approach the interaction among SPET domains in OLED devices. The model is based on an equivalent electrical circuit that merges the electrical, thermal and photometrical behaviour of the OLED and that can easily be implemented in any computer-based simulation program. A detailed procedure for obtaining the different parameters of the proposed model is also presented in this study. The model has been verified for two different OLED geometries, with favourable agreement among theoretical, finite element analysis and experimental results. The results show the influence of scale factor on heat transfer mechanism and the temperature effect on electrical and photometrical OLED performance. This model is useful for predicting OLED behaviour and for simulating OLED drivers during the design of the lighting system.

LEVERAGING 3D-HST GRISM REDSHIFTS TO QUANTIFY PHOTOMETRIC REDSHIFT PERFORMANCE

ABSTRACT We present a study of photometric redshift accuracy in the 3D-HST photometric catalogs, using 3D-HST grism redshifts to quantify and dissect trends in redshift accuracy for galaxies brighter than JH IR &gt; 24 with an unprecedented and representative high-redshift galaxy sample. We find an average scatter of 0.0197 ± 0.0003(1 + z) in the Skelton et al. photometric redshifts. Photometric redshift accuracy decreases with magnitude and redshift, but does not vary monotonically with color or stellar mass. The 1σ scatter lies between 0.01 and 0.03 (1 + z) for galaxies of all masses and colors below z &lt; 2.5 (for JH IR &lt; 24), with the exception of a population of very red (U − V &gt; 2), dusty star-forming galaxies for which the scatter increases to ∼0.1 (1 + z). We find that photometric redshifts depend significantly on galaxy size; the largest galaxies at fixed magnitude have photo-zs with up to ∼30% more scatter and ∼5 times the outlier rate. Although the overall photometric redshift accuracy for quiescent galaxies is better than that for star-forming galaxies, scatter depends more strongly on magnitude and redshift than on galaxy type. We verify these trends using the redshift distributions of close pairs and extend the analysis to fainter objects, where photometric redshift errors further increase to ∼0.046 (1 + z) at . We demonstrate that photometric redshift accuracy is strongly filter dependent and quantify the contribution of multiple filter combinations. We evaluate the widths of redshift probability distribution functions and find that error estimates are underestimated by a factor of ∼1.1–1.6, but that uniformly broadening the distribution does not adequately account for fitting outliers. Finally, we suggest possible applications of these data in planning for current and future surveys and simulate photometric redshift performance in the Large Synoptic Survey Telescope, Dark Energy Survey (DES), and combined DES and Vista Hemisphere surveys.

THE REDMAPPER GALAXY CLUSTER CATALOG FROM DES SCIENCE VERIFICATION DATA

ABSTRACT We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited and contains 786 clusters with richness (roughly equivalent to ) and . The DR8 catalog consists of 26,311 clusters with , with a sharply increasing richness threshold as a function of redshift for . The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the level for , rising to ∼0.02 at in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev–Zeldovich data to show that the centering performance and mass–richness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.

Optimal spectra of white LED integrated with quantum dots for mesopic vision.

The spectral optimization model for limited mesopic luminous efficacy (LLEm) of white LED integrated with quantum dots (QD-WLED) consisting of a blue chip, green, yellow and red quantum dots, including down-conversion energy loss, was developed under constraint of designated color rendering properties. The optimal spectra of QD-WLEDs with CRI ≥ 70 and CQS ≥ 60 as well as CRI ≥ 85 and CQS ≥ 85 for mesopic vision, photometric and colorimetric performances at correlated color temperature of 2700 K to 45000 K, as well as the LLEms of optimal QD-WLEDs for four road lighting standards of the USA and the UK were presented. These results suggest that QD-WLEDs make strong candidates for replacing conventional light sources in the future as they enhance the vision quality in the road lighting in addition to energy saving.

First performance of the GeMS + GMOS system – 1. Imaging

During the commissioning of the Gemini MCAO System (GeMS), we had the opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS), the most utilised instrument at Gemini South Observatory, in March and May 2012. Several globular clusters were observed in imaging mode that allowed us to study the performance of this new and untested combination. GMOS is a visible instrument, hence pushing MCAO toward the visible.We report here on the results with the GMOS instruments, derive photometric performance in term of Full Width Half Maximum (FWHM) and throughput. In most of the cases, we obtained an improvement factor of at least 2 against the natural seeing. This result also depends on the Natural Guide Star constellation selected for the observations and we then study the impact of the guide star selection on the FWHM performance.We also derive a first astrometric analysis showing that the GeMS+GMOS system provide an absolute astrometric precision better than 8mas and a relative astrometric precision lower than 50 mas.

Overconfidence in photometric redshift estimation

We describe a new test of photometric redshift performance given a spectroscopic redshift sample. This test complements the traditional comparison of redshift {\it differences} by testing whether the probability density functions $p(z)$ have the correct {\it width}. We test two photometric redshift codes, BPZ and EAZY, on each of two data sets and find that BPZ is consistently overconfident (the $p(z)$ are too narrow) while EAZY produces approximately the correct level of confidence. We show that this is because EAZY models the uncertainty in its spectral energy distribution templates, and that post-hoc smoothing of the BPZ $p(z)$ provides a reasonable substitute for detailed modeling of template uncertainties. Either remedy still leaves a small surplus of galaxies with spectroscopic redshift very far from the peaks. Thus, better modeling of low-probability tails will be needed for high-precision work such as dark energy constraints with the Large Synoptic Survey Telescope and other large surveys.