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3 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT       # 3333

PERIOD COVERED: DOY 92

Part 2 of 3

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. 

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. 

NICMOS 9484

The NICMOS Parallel Observing Program

We propose to manage the default set of pure parallels with NICMOS.
Our experience with both our GO NICMOS parallel program and the
public parallel NICMOS programs in cycle 7 prepared us to make
optimal use of the parallel opportunities. The NICMOS G141 grism
remains the most powerful survey tool for HAlpha emission-line
galaxies at cosmologically interesting redshifts. It is particularly
well suited to addressing two key uncertainties regarding the global
history of star formation: the peak rate of star formation in the
relatively unexplored but critical 1<= z <= 2 epoch, and the amount
of star formation missing from UV continuum-based estimates due to
high extinction. Our proposed deep G141 exposures will increase the
sample of known HAlpha emission- line objects at z ~ 1.3 by roughly
an order of magnitude. We will also obtain a mix of F110W and F160W
images along random sight-lines to examine the space density and
morphologies of the reddest galaxies. The nature of the extremely red
galaxies remains unclear and our program of imaging and grism
spectroscopy provides unique information regarding both the incidence
of obscured star bursts and the build up of stellar mass at
intermediate redshifts. In addition to carrying out the parallel
program we will populate a public database with calibrated spectra
and images, and provide limited ground- based optical and near-IR
data for the deepest parallel fields.

NICMOS 9485

Completing A Near-Infrared Search for Very Low Mass Companions to
Stars within 10 pc of the Sun

Most stars are fainter and less massive than the Sun. Nevertheless,
our knowledge of very low mass {VLM} red dwarfs and their brown dwarf
cousins is quite limited. Unknown are the true luminosity function
{LF}, multiplicity fraction, mass function, and mass-luminosity
relation for red and brown dwarfs, though they dominate the Galaxy in
both numbers and total mass. The best way to constrain these
relations is a search for faint companions to nearby stars. Such a
search has several advantages over field surveys, including greater
sensitivity to VLM objects and the availability of precise parallaxes
from which luminosities and masses can be derived. We propose to
complete our four-filter NICMOS snapshot search for companions to
stars within 10 pc. With a 10 sigma detection limit of M_J ~ 20 at
10 pc, we can detect companions between 10 and 100 AU that are at
least 9 mag fainter than the empirical end of the main sequence and
at least 6.5 mag fainter than the brown dwarf Gl 229B. When
completed, our search will be the largest, most sensitive,
volume-limited search for VLM companions ever undertaken. Our
four-filter search will permit unambiguous identification of
VLM-companion candidates for follow-up observation. Together with IR
speckle and deep imaging surveys, our program will firmly establish
the LF for VLM companions at separations of 1-1000 AU and the
multiplicity fraction of all stars within 10 pc. 

WFPC2 9594

WFPC2 CYCLE 11 SUPPLEMENTAL DARKS pt2/3

This dark calibration program obtains 3 dark frames every day to
provide data for monitoring and characterizing the evolution of hot
pixels 

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

STIS 9608

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.

 - Continued -

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