The inherent nonlinear response of infrared detectors limits the ultimate photometric accuracy that can be obtained. In this paper we show that, by limiting the observations to a fraction of the full dynamic range, we can decrease the variance of the corrected residuals. This improvement is due both to a more accurate nonlinearity correction solution and to a reduction in the number of pixels affected by saturation in neighboring pixels. We compare several metrics of goodness-of-fit for non-linearity corrected integrations over a range of full well fractions. We show that, by limiting the operational dynamic, we can improve the quality of the non-linearity corrections and increase the number of science-grade pixels. We find that when we limit the dynamic range to 80% of the full well, the variance of the residuals decreases by a factor of two and that other metrics of slope consistency show even larger improvements.

We present the analysis of James Webb Space Telescope near-infrared H2RG detectors with a 5-mu m cutoff, which shows that, at temperatures <60 K, there is no measurable dark current. Instead, the observed signal in dark exposures is almost entirely due to multiplexer glow that arises as each pixel is selected. We are able to separate the per-sample glow from the time-dependent dark current by comparing the observed signal in both continuous and sparsely sampled dark exposures. Such explicit tests are required to break the degeneracy between dark current and uniform amplifier glow. We show that the glow is lower within the regions of the detector that are missing the epoxy back fill (voids). We also find that the glow from each pixel extends out to a radius of several pixels. Because of the higher sampling frequency of subarray observations, the per-sample glow leads to a higher apparent dark current in subarray exposures. Finally, we show that the magnitude of the glow is affected by the pixel source follower current, the pixel clocking rate, and the number of outputs running in parallel. Our measurement of an insignificant dark current shows that the detector noise is no longer limited by the quality of the mercury cadmium telluride layer but instead by the multiplexer and readout electronics. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

The persistent signal from bright sources in infrared detectors can significantly pollute subsequent images. While the persistent signal is a small fraction of the stimulus image, the high dynamic range of modern infrared detectors allows this signal to be easily detectable. In this paper we present a method of characterizing the persistence signal over time as a function of the length of time that the bright signal is left on the detector and the number of traps in each pixel. We derive the functional form for both the capture and decay of traps and show that it is analogous to radioactive decay. We show that a model with three exponential families of traps is able to explain the observed persistence. We use electronically induced persistence to simulate a flash of light and show that the observed difference between the electronically induced persistence signal and that from light induced saturation is well fit by our model. The fitted parameters for the tested part show a very fast capture rate for the tested detector. This very fast capture is significantly different than what we found for an engineering part we had tested earlier We then derive and test the capture model for the more real-world situation of the continuous accumulation of charge during an exposure. We use this model to predict the persistence from a given stimulus image that we then remove from the darks after the stimulus image. The resulting corrected darks show that over 90% of the persistence was removed.

The Mid-Infrared Instrument (MIRI) is one of four science instruments to be flown aboard the James Webb Space Telescope (JWST). MIRI operates from 5 to 28.5 microns and provides a suite of versatile capabilities including imaging, low resolution spectroscopy (LRS), medium-resolution spectroscopy (MRS) via an integral field unit, and coronagraphy. The MIRI pipeline consists of three stages: 1) Raw to Slope Images, 2) Calibrated Slope Images, and 3) Multiple Exposures Combined. The pipeline is designed to provide well-calibrated, high level data products that maximize the scientific return from the instrument.

The MIRI Si:As IBC detector arrays extend the heritage technology from the Spitzer IRAC arrays to a 1024 x 1024 pixel format. We provide a short discussion of the principles of operation, design, and performance of the individual MIRI detectors, in support of a description of their operation in arrays provided in an accompanying paper (Ressler et al. (2015)). We then describe modeling of their response. We find that electron diffusion is an important component of their performance, although it was omitted in previous models. Our new model will let us optimize the bias voltage while avoiding avalanche gain. It also predicts the fraction of the IR-active layer that is depleted (and thus contributes to the quantum efficiency) as signal is accumulated on the array amplifier. Another set of models accurately predicts the nonlinearity of the detector-amplifier unit and has guided determination of the corrections for nonlinearity. Finally, we discuss how diffraction at the interpixel gaps and total internal reflection can produce the extended cross-like artifacts around images with these arrays at short wavelengths, ~ 5 microns. The modeling of the behavior of these devices is helping optimize how we operate them and also providing inputs to the development of the data pipeline.

We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in starburst, or the fraction of high mass stars in the bursts is increased towards the bright end of the LF.

We measure the quantum efficiency and quantum yield of an H2RG HgCdTe near-infrared sensor array. Using a blackbody, narrowband filters, and a pinhole camera to provide a calibrated irradiance on the HgCdTe sensor, we determine a 2 σ lower limit of 85% for the quantum efficiency averaged over the array and over three observed wavelengths, 3.38, 3.9, and 4.5 μm. The peak quantum efficiency occurs near the center of the sensor and is unity within measurement uncertainty (5%). By substituting a calibrated PbSe diode for the H2RG sensor, we verify the methods and equipment at the three wavelengths, 3.38, 3.9, and 4.5 μm. Accurate measurement of the quantum efficiency requires a well-calibrated system gain, the determination of which is complicated by interpixel capacitance, which correlates noise between adjacent pixels. If unaccounted for, the correlation induced by interpixel capacitance would cause the system gain and hence the quantum efficiency to be overestimated by ∼20%. We accurately measure the interpixel capacitance using the autocorrelation method of Brown, Schubnell, and Tarlé and by a method described in this paper that uses post-readout binning. The two methods yield consistent results, but the binning method is more robust than the autocorrelation method in the presence of electromagnetic interference. The interpixel capacitance we measure for the H2RG-S010 sensor is similar to that of another epoxy-backfilled H2RG sensor tested recently by Brown, Schubnell, and Tarlé. Using the same PbSe diode to calibrate the quantum efficiency of the 5.5-μm-cutoff H2RG sensor from 0.7 μm to 6.0 μm, and correcting for the interpixel capacitance, we derive implausible quantum efficiencies greater than unity between 1.4 μm and 2.4 μm that we cannot explain. The apparent system gain, measured at many monochromatic wavelengths with the usual variance-versus-mean photon-transfer analysis of flat-field images, is a function of wavelength for wavelengths less than 2 μm, which we interpret as evidence for quantum yield larger than unity, i.e., more than one electron being produced by each photon detected by the sensor. We derive the effects of Fano noise and quantum yield on the photon-transfer curve.

This document summarizes the NICMOS Calibration Plans for Cycle 15. The monitoring programs from the previous Cycle 13 and 14 are carried out in Cycle 15. Additional calibration is included in order to improve the accuracy of previously archived NICMOS data.

This paper summarizes the NICMOS Calibration Plans for Cycles 13 and 14. These plans complement the SMOV3b, the Cycle 10 (interim), and the Cycles 11 and 12 (regular) calibration programs executed after the installation of the NICMOS Cooling System (NCS). The special calibrations on Cycle 13 were focussed on a follow up of the spectroscopic recalibration initiated in Cycle 12. This program led to the discovery of a possible count rate non-linearity, which has triggered a special program for Cycle 13 and a number of subsequent tests and calibrations during Cycle 14. At the time of writing this is a very active area of research. We also briefly comment on other calibrations defined to address other specific issues like: the autoreset test, the SPARS sequence tests, and the low-frequency flat residuals for NIC1. The calibration programs for the 2-Gyro campaigns are not included here, since they have been described elsewhere (see Sembach et al. 2006, in these proceedings). Further details and updates on specific programs can be found via the NICMOS web site.

This paper presents the Hubble Ultra Deep Field (HUDF), a one million second exposure of an 11 square minute-of-arc region in the southern sky with the Advanced Camera for Surveys on the Hubble Space Telescope using Director’s Discretionary Time. The exposure time was divided among four filters, F435W (B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately uniform limiting magnitudes mAB ∼ 29 for point sources. The image contains at least 10,000 objects presented here as a catalog, the vast majority of which are galaxies. Visual inspection of the images shows few if any galaxies at redshifts greater than ∼ 4 that resemble present day spiral or elliptical galaxies. The image reinforces the conclusion from the original Hubble Deep Field that galaxies evolved strongly during the first few billion years in the infancy of the universe. Using the Lyman break dropout method to derive samples of galaxies at redshifts between 4 and 7, it is possible to study the apparent evolution of the galaxy luminosity function and number density. Examination of the catalog for dropout sources yields 504 B435-dropouts, 204 V606-dropouts, and 54 i775-dropouts. The i775-dropouts are most likely galaxies at redshifts between 6 and 7. Using these samples that are at different redshifts but derived from the same data, we find no evidence for a change in the characteristic luminosity of galaxies but some evidence for a decrease in their number densities between redshifts of 4 and 7. Assessing the factors needed to derive the luminosity function from the data suggests there is considerable uncertainty in parameters from samples discovered with different instruments and derived using independent assumptions about the source populations. This assessment calls into question some of the strong conclusions of recently published work on distant galaxies. The ultraviolet luminosity density of these samples is dominated by galaxies fainter than the characteristic luminosity, and the HUDF reveals considerably more luminosity than shallower surveys. The apparent ultraviolet luminosity density of galaxies appears to decrease from redshifts of a few to redshifts greater than 6, although this decrease may be the result of faint-end incompleteness in the most distant samples. The highest redshift samples show that star formation was already vigorous at the earliest epochs that galaxies have been observed, less than one billion years after the Big Bang. Subject headings: astronomical data bases: miscellaneous — cosmology: early universe — galaxies: evolution — galaxies: high-redshift Space Telescope Science Institute Johns Hopkins University McDonald Observatory, University of Texas European Space Agency European Southern Observatory Space Telescope European Coordinating Facility US Naval Observatory, Flagstaff Station University of Texas Max-Planck-Institut für Astronomie

This paper presents the Hubble Ultra Deep Field (HUDF), a 1 million s exposure of an 11 arcmin2 region in the southern sky with the Advanced Camera for Surveys on the Hubble Space Telescope using Director's Discretionary Time. The exposure time was divided among four filters, F435W (B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately uniform limiting magnitudes mAB ∼ 29 for point sources. The image contains at least 10,000 objects, presented here as a catalog, the vast majority of which are galaxies. Visual inspection of the images shows few if any galaxies at redshifts greater than ∼4 that resemble present-day spiral or elliptical galaxies. The image reinforces the conclusion from the original Hubble Deep Field that galaxies evolved strongly during the first few billion years in the infancy of the universe. Using the Lyman break dropout method to derive samples of galaxies at redshifts between 4 and 7, it is possible to study the apparent evolution of the galaxy luminosity function and number density. Examination of the catalog for dropout sources yields 504 B435 dropouts, 204 V606 dropouts, and 54 i775 dropouts. The i775 dropouts are most likely galaxies at redshifts between 6 and 7. Using these samples, which are at different redshifts but derived from the same data, we find no evidence for a change in the characteristic luminosity of galaxies but some evidence for a decrease in their number densities between redshifts of 4 and 7. Assessing the factors needed to derive the luminosity function from the data suggests that there is considerable uncertainty in parameters from samples discovered with different instruments and derived using independent assumptions about the source populations. This assessment calls into question some of the strong conclusions of recently published work on distant galaxies. The ultraviolet luminosity density of these samples is dominated by galaxies fainter than the characteristic luminosity, and the HUDF reveals considerably more luminosity than shallower surveys. The apparent ultraviolet luminosity density of galaxies appears to decrease from redshifts of a few to redshifts greater than 6, although this decrease may be the result of faint-end incompleteness in the most distant samples. The highest redshift samples show that star formation was already vigorous at the earliest epochs at which galaxies have been observed, less than 1 billion years after the big bang.

We provide an overview of the most important calibration aspects of the NICMOS instrument on board of HST. We describe the performance of the instrument after the installation of the NICMOS Cooling System, and show that the behavior of the instrument has become very stable and predictable. We detail the improvements made to the NICMOS pipeline and outline plans for future developments. The derivation of the absolute photometric zero-point calibration is described in detail. Finally, we describe and quantify a newly discovered count-rate dependent non-linearity in the NICMOS cameras. This new non-linearity is distinctly different from the total count dependent non-linearity that is well known for near-infrared detectors. We show that the non-linearity has a power law behavior, with pixels with high system, or vice versa, pixels with low count rate detecting slightly less than expected. The effect has a wavelength dependence with observations at the shortest wavelengths being the most affected ( 0.05-0.1 mag per dex flux change at 1 micron, 0.03 mag per dex at 1.6 micron).