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18 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT #3344

PERIOD COVERED:  DOY 107

Part 2 of 3

ACS 9454

The Nature of the UV Continuum in LINERs: A Variability Test

LINERs may be the most common AGNs, and the signposts of accretion
onto the massive black holes present in most galaxies. However, the
LINER spectrum is the result of UV excitation, and, in at least some
LINERs, a nuclear cluster of hot stars, rather than an AGN, dominates
the energetics in the UV. Thus, it is still unknown if the UV
continuum, or the optical emission lines it excites, have anything to
do with an AGN. The demographics and accretion physics of
low-luminosity GNs hinge on this question. We propose to search for
variability in a sample of 17 LINERs with compact UV nuclei.
Variability can reveal an AGN component in the UV continuum, even
when its light is not dominant. We will test systematically the
handful of non-definitive reports of UV variability, and potentially
quantify the AGN contribution to the UV emission. Variability in all
or most objects will be strong evidence that LINERs mark dormant AGNs
in most galaxies. Alternatively, a general null detection of
variability will suggest that, even in LINERs with additional AGN
signatures, the UV continuum is stellar in origin.  Contemporaneous
monitoring with the VLA/VLBA of 11 objects which have radio cores
{five of which we already know are radio-variable} will reveal the
relations between UV and radio variations. The UV-variable objects
will be targeted for future, better-sampled, monitoring.

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 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.

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. 

STIS 9614

STIS CCD Imaging Flats C11

Investigate flat-field stability over a monthly period.

 - Continued -

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