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HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3155

PERIOD COVERED: DOYs 122-124

Part 1 of 5

OBSERVATIONS SCHEDULED

ACS 9651

ACS CCD Flash Calibration

This activity provides a set of CCD FLASH exposure reference images
for each current level/shutter-side/detector combination, for the
pair of FLASH LEDs on the instrument side currently in use. It also
tests the short-term repeatability at the shortest FLASH exposure
times that are expected to be used {1.0 sec}. 

ACS 9468

ACS Grism Parallel Survey of Emission- line Galaxies at Redshift
z =07pl 7

We propose an ACS grism parallel survey to search for emission-line
galaxies toward 50 random lines of sight over the redshift interval
0 < z=07pl 7. We request ACS parallel observations of duration more
than one orbit at high galactic latitude to identify ~ 300 HAlpha
emission-line galaxies at 0.2=07p= lz=07pl 0.5, ~ 720 O IILambda3727
emission-line galaxies at 0.3=07pl z=07pl 1.68, and =07pg 1000
Ly-alpha emission-line galaxies at 3=07pl z=07pl 7 with total
emission line flux f=07pg 2* 10^-17 ergs s^-1 cm^-2 over 578
arcmin^2. We will obtain direct images with the F814W and F606W
filters and dispersed images with the WFC/G800L grism at each
position. The direct images will serve to provide a zeroth order
model both for wavelength calibration of the extracted 1D spectra
and for determining extraction apertures of the corresponding
dispersed images. The primary scientific objectives are as follows:
{1} We will establish a uniform sample of HAlpha and O II
emission-line galaxies at z<1.7 in order to obtain accurate
measurements of co-moving star formation rate density versus redshift
over this redshift range. {2} We will study the spatial and
statistical distribution of star formation rate intensity in
individual galaxies using the spatially resolved emission-line
morphology in the grism images. And {3} we will study high-redshift
universe using Ly-alpha emitting galaxies identified at z=07pl 7 in
the survey. The data will be available to the community immediately
as they are obtained.

ACS 9657

ACS Internal Flat Field Stability

The flat field stability and characterization obtained during the
ground calibration and SMOV phases will be tested and verified
through a sub-sample of the filter set. Only internal exposures with
the calibration lamps will be required.

ACS 9482

ACS Pure Parallel Lyman-Alpha Emission Survey {APPLES}

Ly-alpha line emission is an efficient tool for identifying young
galaxies at high redshift, because it is strong in galaxies with
young stars and little or no dust --- properties expected in galaxies
undergoing their first burst of star- formation. Slitless
spectroscopy with the ACS Wide-Field Camera and G800L grism allows an
unmatched search efficiency for such objects over the uninterrupted
range 4 <~ z <~ 7. We propose the ACS Pure Parallel Ly-alpha Emission
Survey {``APPLES''}, to exploit this unique HST capability and so
obtain the largest and most uniform sample of high redshift Ly-alpha
emitters yet. Parallel observations will allow this survey to be
conducted with minimal impact on HST resources, and we will place
reduced images and extracted spectra in the public domain within
three months of observation. We aim to find ~ 1000 Ly-alpha emitters,
5 times the biggest current sample of Ly-alpha emitters.  This
unprecedented sample will provide robust statistics on the
populations and evolution of Ly-alpha emitters between redshifts
4--7; a robust measurement of the reionization redshift completely
independent of the Gunn-Peterson trough; spatial clustering
information for Ly-alpha emitters which would let us probe their bias
function and hence halo mass as a function of redshift; many galaxies
at redshift exceeding 6; and lower redshift serendipitous
discoveries. 

ACS 9674

CCD Daily Monitor

This program consists of basic tests to monitor, the read noise, the
development of hot pixels and test for any source of noise in ACS CCD
detectors. This programme will be executed once a day for the entire
lifetime of ACS. 

ACS 9480

Cosmic Shear With ACS Pure Parallels

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 textiti {F775W} we will measure for the
first time: beginlistosetlength sep0cm setlengthemsep0cm setlength
opsep0cm em the cosmic shear variance on scales <0.7 arcmin, em the
skewness of the shear distribution, and em the magnification effect.
endlist Our measurements will determine the amplitude of the mass
power spectrum sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20,
and the mass density Omega_m with s/n=3D4. 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. 

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