SLACS for the Masses: Extending Strong Lensing to Lower Masses and Smaller Radii
Strong gravitational lensing provides the most accurate possible measurement of mass in the central regions of early-type galaxies (ETGs). We propose to continue the highly productive Sloan Lens ACS (SLACS) Survey for strong gravitational lens galaxies by observing a substantial fraction of 135 new ETG gravitational-lens candidates with HST-ACS WFC F814W Snapshot imaging. The proposed target sample has been selected from the seventh and final data release of the Sloan Digital Sky Survey, and is designed to complement the distribution of previously confirmed SLACS lenses in lens-galaxy mass and in the ratio of Einstein radius to optical half-light radius. The observations we propose will lead to a combined SLACS sample covering nearly two decades in mass, with dense mapping of enclosed mass as a function of radius out to the half-light radius and beyond. With this longer mass baseline, we will extend our lensing and dynamical analysis of the mass structure and scaling relations of ETGs to galaxies of significantly lower mass, and directly test for a transition in structural and dark-matter content trends at intermediate galaxy mass. The broader mass coverage will also enable us to make a direct connection to the structure of well-studied nearby ETGs as deduced from dynamical modeling of their line-of-sight velocity distribution fields. Finally, the combined sample will allow a more conclusive test of the current SLACS result that the intrinsic scatter in ETG mass-density structure is not significantly correlated with any other galaxy observables. The final SLACS sample at the conclusion of this program will comprise approximately 130 lenses with known foreground and background redshifts, and is likely to be the largest confirmed sample of strong-lens galaxies for many years to come.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
CCD Bias Monitor-Part 2
Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
JWST Calibration from a Consistent Absolute Calibration of Spitzer & Hubble
Recently, Gordon, Bohlin, et al. submitted a successful Spitzer proposal for cross calibration of HST and Spitzer. The cross-calibration targets are stars in three categories: WDs, A-stars, and G-stars. Traditionally, IR flux standards are extrapolations of stellar models that are tied to absolute fluxes at shorter wavelengths. HST absolute flux standards are among the best available with a solid basis that uses pure hydrogen models of hot WD stars for the SED slopes and is tied to Vega at 5556A via precise Landolt V-band photometry. Consistently matching models to our three categories of HST observations along with Spitzer photometry and the few existing absolute IR flux determinations will provide a solid basis for JWST flux calibration over its 0.8-30micron range. The goal of this proposal is to complete the HST observations of the set of HST/Spitzer cross-calibration stars. Using a variety of standard stars with three different spectral types will ensure that the final calibration is not significantly affected by systematic uncertainties.
Mapping Ganymede's Time Variable Aurora in the Search for a Subsurface Ocean
A very exciting, unresolved question about Jupiter?s moon Ganymede is whether Ganymede harbors a saline subsurface water ocean under its icy crust. A saline, electrically conductive water ocean will modify Ganymede's magnetic field environment and thus also the locations of Ganymede's northern and southern aurora ovals. Without an ocean, Ganymede's aurora ovals will rock by ~10 degrees towards and away from Jupiter within 5.25 hours. However, with an ocean the shift will be up to only ~4 degrees. We propose two visits of five consecutive STIS orbits at eastern elongation to monitor and resolve with sufficient precision the shift in locations of Ganymede's aurora ovals to determine whether an ocean is present on Ganymede. Addressing this question is timely as NASA/ESA are planning a Jupiter system mission including a Ganymede orbiter with the objective to characterize Ganymede as potential habitat.
IR Zero Points
We will measure and monitor the zeropoints through the IR filters using observations of the white dwarf standard stars, GD153, GD71 and GD191B2B and the solar analog standard star, P330E. Data will be taken monthly during Cycle 17. Observations of the star cluster, NGC 104, are made twice to check color transformations. We expect an accuracy of 2% in the wide filter zeropoints relative to the HST photometric system, and 5% in the medium- and narrow-band filters.
Determining the Physical Nature of a Unique Giant Lya Emitter at z=6.595
We propose deep WFC3/IR imaging for a giant Lya emitter (LAE) with a Keck spectroscopic redshift of z=6.595 discovered by extensive narrow-band imaging with Subaru in the SXDS-UKIDSS/UDS field. This remarkable object is unique in many respects including its large stellar mass and luminous nebula which extends over 17 kpc; no equivalent source has been found in other surveys. The nature of this rare object is unclear. Fundamental to progress is determining the origin of star formation in such an early massive object; if the age of the stellar population is short we are likely witnessing a special moment in the formation history of a massive galaxy. The heating source for the nebula is also unclear; options include intense star formation, the infall of cold gas onto a dark halo or shock heating from a merger. We will take deep broad-band (F125W and F160W) images and an intermediate-band (F098M) image which will be analyzed in conjunction with ultra-deep IRAC 3.6 and 4.5 micron data being taken by the Spitzer/SEDS project. These data will enable us to constrain the star formation rate and stellar age. Moreover, the UV continuum morphology and Lya-line distribution will be investigated for evidence of a major merger, cold accretion, or hot bubbles associated with outflows. We will address the physical origin of the remarkable object observed at an epoch where massive galaxies are thought to begin their assembly.
Differentiation in the Kuiper belt: a Search for Silicates on Icy Bodies.
We currently have a large on-going program (Go Program 11644, 120 orbits) to exploit the superb stability and photometric characteristics of HST and the broad range in wavelength coverage of the WFC3 to make broad-band vis/IR spectral observations of a large sample of Kuiper belt objects. Though the survey is currently only ~50% complete, the quality and unprecedented signal-to-noise of these observations has revealed the existence of a previously undiscovered spectral variability not explainable within our current understanding of these objects.
A possible explanation for this variability is that with this faint set of Kuiper belt objects, we are beginning to see the difference between larger differentiated objects and smaller non-differentiated objects. Its seems that the small and likely undifferentiated objects are exhibiting silicate features that affect our photometry - features not exhibited by the icy mantles of larger icy bodies.
We propose a small add-on survey to dramatically increase the scientific results of our large program. The proposed observations will use the proven capabilities of WFC3 to make broad and narrow-band photometric observations to detect spectral features in the 1.0-1.3 micron range of a small subset of our sources. The 13 targets have been carefully selected to cover the range of spectral variability detected in our large program as well as sample the entire dynamical range and physical sizes of these targets. These observations will allow the identification of undifferentiated Kuiper belt objects by detection of their silicate features. As a probe for differentiation, these observations could constrain the natal locations of different Kuiper belt classes, a constraint currently unavailable to formation models. This small set of observations will allow the calibration of the spectral variability seen in our large program, and drastically enhance the scientific output of our full Cycle 17 sample.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
UVIS Internal Flats
This proposal will be used to assess the stability of the flat field structure for the UVIS detector throughout the 15 months of Cycle 17. The data will be used to generate on-orbit updates for the delta-flat field reference files used in the WFC3 calibration pipeline, if significant changes in the flat structure are seen.