1807.05217
Persistence characterization of teledyne H2RG detectors
Tulloch
Image persistence is a major problem in IR detectors, potentially seriously limiting data quality in many observational regimes. The problem manifests itself as remnant images that can persist for several days after a deep exposure. In this study, the persistence behavior of three 5.3 um cutoff H2RGs has been characterized using a low-background cryostat with LED light sources. Persistence charge de-trapping was measured over several hours following a wide range of exposure levels and exposure times. This data was then analyzed to yield charge trapping and de-trapping spectra which present graphically the trap density as a function of their time constants. These spectra show the detector behavior in a very direct way and offer a natural metric for comparing different devices. It is hoped that the trap time constant spectra for each detector can be used in an analysis pipeline to remove persistence artifacts based on the recent exposure history of the detector. The study confirmed that the charge traps responsible for persistence must be present in the depletion region fo the pixel, however, two trap populations were revealed. One of these captures charge within milliseconds and then releases it over many hours. The second population is less problematic with fairly similar trapping and de-trapping time constants. Large differences in persistence magnitude and trap spectra have been found even between devices with near-consecutive serial numbers. Lower temperatures results in lower persistence both in terms of total trapped chart and the time taken for that charge to decay. Limiting the full-well by reducing pixel bias voltage also had a beneficial effect. Previously proposed mitigation techniques including "global reset de-trapping" and "night light" illumination were tried but found to be ineffective.
1807.05667
A standard siren measurement of the Hubble constant from GW170817 without the electromagnetic counterpart
Fishbach, et al
Perform a statistical standard siren analysis of GW170817. The analysis does not utilize knowledge of NGC 4993 as the unique host galaxy of the optical counterpart to GW170817. Instead, consider each galaxy within the GW170817 localization region as a potential host; combining the H0 values from all the galaxies provides a final measurement of H0. Explore the dependence of the results on the galaxy thresholds, as well as the impact of weighting the galaxies by stellar mass and SFR. Considering all galaxies brighter than 0.01 L*_B (containing ~99% of the total blue luminosity) as equally likely to host a BNS merger, find H0=76+48-23 km/s/Mpc (maximum a posteriori and 68.3% highest density posterior interval; all results are from publicly available LIGO/Virgo sky maps using approximations to the line-of-sight distance distributions). Restricting only to galaxies brighter than 0.626 L*_B (containing ~50% of the total blue luminosity) tightens the measurement to H0=77+37-18 km/s/Mpc. Show that the weighting the host galaxies by stellar mass or SFR provides entirely consistent results with potentially tighter constraints. While these statistical estimates are inferior to the value from the counterpart standard siren measurement utilizing NGC 4993 as the unique host, the analysis is a proof-of-principle demonstration of the statistical approach first proposed by Bernard Schutz over 30 years ago. This method is of particular promise in the case of binary BHs, since they are not expected to have optical counterparts, and they occur at sufficient rate that the combined statistical standard siren measurements from many events may offer precision measurements of the luminosity distance-redshift relation to high (z<~1) redshift.
1807.06025
The distance of the dark matter deficient galaxy NGC1052-DF2
van Dokkum, Danieli, Cohen, Conroy
Recently have inferred that the galaxy NGC1052-DR2 has little of no dark matter and a rich system of unusual globular clusters. Assumed that the galaxy is a satellite of the luminous elliptical galaxy NGC1052vat ~20 Mpc, on the basis of its surface brightness fluctuations (SBF) distance of 19.0±1.7 Mpc, its radial velocity of ~1800 km/s, and its projected position. Trujillo+ 2018 proposed a much closer distance of 13 Mpc, based largely on ta putative detection of the tip of the red giant branch (TRGB) in the color-magnitude diagram (CMD) and a recalibration of the SBF measurement. Here, analyze the CMD using both fully population galaxy models and other galaxies in the HST sample, and demonstrate the Trujillo+ almost certainly confused blends for individual red giants in their analysis. These blends produce a "phantom" TRGB ~2 times brighter than the true TRGB, leading to a ~1.4 times smaller inferred distance. The large population of unblended stars on the red giant branch expected for distances of ~13 Mpc is not detected in the HST data. Also provide a new distance measurement to NGC1052-DR2 that is free of calibration uncertainties, by anchoring it to a satellite of the megamaser host galaxy NGC4258. From a megamaser-TRGB-SBF distance ladder, obtain D-18.7 ±1.7 Mpc, consistent with the previous measurement and with the distance to NGC1052.
1807.06658
All transverse motion is peculiar: connection the proper motions of galaxies to the matter power spectrum
Darling, Truebenbach
In an isotropic and homogenous Hubble expansion, all transverse motion is peculiar. Like the radial peculiar velocities of galaxies, transverse peculiar velocities are a means to trace the density of matter that does not rely on light tracing mass. Unlike radial peculiar velocity measurements that require precise redshift-independent distances in order to distinguish between the Hubble expansion and the observed redshift, transverse peculiar velocities can be measured using redshifts alone as a proxy for distance. Extragalactic proper motions can therefore directly measuring peculiar velocities and probe the matter power spectrum. Develop 2pt transverse velocity correlation statistics and demonstrate their dependence on the matter power spectrum. Predict the power in these correlation statistics as a function of the physical separation, angular separation, and distance of pairs of galaxies and demonstrate that the effect of large scale structure on transverse motions is best measured for pairs of objects with comoving separations less than about 50 Mpc. Transverse peculiar velocities induced by large scale structure should be observable as proper motions using long baseline radio interferometry or space-based optical astrometry.
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