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21 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT     #3345

PERIOD COVERED:  DOY 108-110

Part 1 of 5

OBSERVATIONS SCHEDULED


ACS 9658

ACS Earth Flats

This program will obtain sequences of flat field images by observing
the bright Earth. Several UV filters from the interim calibration
program {9564} require additional exposures to obtain the required
illumination. A few UV filters from this program will be repeated to
monitor for changes in the flat fields and to verify the interim
results. Since no streaks are observed in the UV, the wavelength
coverage is extended to longer wavelengths in order to explore the
severity of streaks in the flats from clouds in the FOV. We have
added exposures for the HRC in the visible filters to verify the
results derived from the L-flat campaign and to explore the severity
of streaks. We have also added exposures on WFC using the minimum
exposure time and using filters which will not saturate the brightest
WFC pixel by more than 10 times the full well. 

ACS 9468

ACS Grism Parallel Survey of Emission- line Galaxies at Redshift
z pl 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 < zpl 7. We request ACS parallel observations of duration more than
one orbit at high galactic latitude to identify ~ 300 HAlpha
emission-line galaxies at 0.2pl zpl 0.5, ~ 720 O IILambda3727
emission-line galaxies at 0.3pl zpl 1.68, and pg 1000 Ly-alpha
emission-line galaxies at 3pl zpl 7 with total emission line flux fpg
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 pl 7 in the
survey. The data will be available to the community immediately as
they are obtained.

ACS 9673

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=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.

ACS 9476

Galaxy Evolution in the Richest Clusters at z=0.8: the EDisCS Cluster
Sample

The study of distant cluster galaxies requires two key ingredients:
{1} deep high-resolution imaging, to constrain galaxy structure; and
{2} 8m-class spectroscopy, to measure stellar content, star-formation
rates, dynamics, and cluster membership. We will reach both
conditions with the addition of HST/ACS imaging to our suite of VLT
{36 nights} and NTT {20 nights} observations of 10 confirmed clusters
at z~0.8, drawn from the ESO Distant Cluster Survey {EDisCS}. The
proposed HST/ACS data will complement our existing optical/IR imaging
and spectroscopy with quantitative measures of cluster galaxy
morphologies {i.e. sizes and shapes, bulge-disk decompositions,
asymmetry parameters}, and with measurements of cluster masses via
weak lensing. Major advantages unique to the EDisCS project include:
{i} uniform selection of clusters; {ii} large enough sample sizes to
characterize the substantial cluster-to-cluster variation in galaxy
populations; {iii} large quantities of high quality data from 8m
telescopes; {iv} uniform measurements of morphologies, spectroscopic
and photometric redshifts, SEDs, star-formation/AGN activities, and
internal kinematics; {v} optical selection of clusters to complement
the X-ray selection of almost all high-z clusters in the ACS GTO
programs; {vi} forefront numerical simulations designed specifically
to allow physical interpretation of observed differences between the
high-z and local clusters. 

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