9578( 6) - 01/06/03 10:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9578 Version: 6 Check-in Date: 06-Jan-2003 10:42:20 1.Proposal Title: Cosmic Shear With ACS Pure Parallels. Targeted Portion. ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Jason Rhodes NASA Goddard Space Flight Center CoI: Dr. Alexandre Refregier Institute for Astronomy, Cambridge N University CoI: Dr. Jonathan P. Gardner Goddard Space Flight Center N CoI: Mr. Nicholas Collins Goddard Space Flight Center N ------------------------------------------------------------------------------------ 5. Abstract Small distortions in the shapes of background galaxies by foreground mass provide a powerful method of directly measuring the amount and distribution of dark matter. Several groups have recently detected this weak lensing by large-scale structure, also called cosmic shear. The high resolution and sensitivity of HST/ACS provide a unique opportunity to measure cosmic shear accurately on small scales. Using 260 parallel orbits in Sloan i (F775W) we will measure for the first time: the cosmic shear variance on scales <0.7 arcmin, the skewness of the shear distribution, and the magnification effect. Our measurements will determine the amplitude of the mass power spectrum sigma_8 Omega_m^0.5, with signal-to-noise (s/n) ~ 20, and the mass density Omega_m with s/n=4. They will be done at small angular scales where non- linear effects dominate the power spectrum, providing a test of the gravitational instability paradigm for structure formation. Measurements on these scales are not possible from the ground, because of the systematic effects induced by PSF smearing from seeing. Having many independent lines of sight reduces the uncertainty due to cosmic variance, making parallel observations ideal. ------------------------------------------------------------------------------------ 9578( 6) - 01/06/03 10:43 - [ 2] Observations Description ------------------------ Although the geometric distortion in ACS is quite large, this effect is stable and easily corrected. Astrometric shifts in stellar fields will be used to calculate the geometric distortion in ACS early in the instrument's lifetime (SMOV calibration proposal GO-9028). The ellipticities induced by the PSF are small. However, due to the small size of the galaxies we will be studying, a correction for the PSF, which is expected to vary slightly with time, is necessary. M4 globular cluster images will be used for calibration of the PSF as we have done previously for WFPC2 and STIS. We propose using the same fields we used for the WFPC2 calibrations, which contain roughly 1500-2000 stars with magnitudes 16 Visit Requirements: BEFORE 01-Aug-2002 On Hold Comments: Additional Comments: If possible, visit should be done immediately before secondary mirror repositioning. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=2 1 720 S PATTERN 3 1 IB C Comments: Do not exceed 360 seconds per exposure. ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=NO 1 360 S IB C ------------------------------------------------------------------------------------------------------------------------------------ 9578( 6) - 01/06/03 10:43 - [ 7] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 01-Jan-2003 AND 31-Jan-2003 On Hold Comments: Additional Comments: If possible, visit should be done immediately after secondary mirror repositioning. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=2 1 720 S PATTERN 3 1 IB C Comments: Do not exceed 360 seconds per exposure. ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=NO 1 360 S IB C ------------------------------------------------------------------------------------------------------------------------------------ 9578( 6) - 01/06/03 10:43 - [ 8] Visit: 03 Visit Priority: Visit Requirements: AFTER 01-Jun-2003 On Hold Comments: Additional Comments: If possible, visit should be done approximately 3 months after secondary mirror repositioning. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=2 1 720 S PATTERN 3 1 IB C Comments: Do not exceed 360 seconds per exposure. ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6121-CAL ACS/WF ACCUM WFC F775W CR-SPLIT=NO 1 360 S IB C ------------------------------------------------------------------------------------------------------------------------------------ 9578( 6) - 01/06/03 10:43 - [ 9] Summary Form for Proposal 9578 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-Aug-2002 PATTERN 3 1 BETWEEN 01-Jan-2003 AND 31-Jan-2003 AFTER 01-Jun-2003 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F775W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6121-CALIB ------------------------------------------------------------------------------------------------------------------------------------