Status Report

HST Daily Report # 3278 – Part 1

By SpaceRef Editor
January 13, 2003
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HST Daily Report # 3278 – Part 1





ACS 9472

A Snapshot Survey for Gravitational Lenses among z >= 4.0 Quasars

Over the last few years, the Sloan Digital Sky Survey has revolutionized the
study of high-redshift quasars by discovering over 200 objects with redshift
greater than 4.0, more than doubling the number known in this redshift
The sample includes eight of the ten highest redshift quasars known. We propose
a snapshot imaging survey of a well-defined sample of 250 z > 4.0 quasars in
order to find objects which are gravitationally lensed. Lensing models
magnification bias predict that at least 4% of quasars in a flux-limited sample
at z > 4 will be multiply lensed. Therefore this survey should find of order 10
lensed quasars at high redshift; only one gravitationally lensed quasar is
currently known at z > 4. This survey will provide by far the best sample to
date of high-redshift gravitational lenses. The observed fraction of lenses can
put strong constraints on cosmological models, in particular on the
constant Lambda. In addition, magnification bias can significantly bias
estimates of the luminosity function of quasars and the evolution thereof; this
work will constrain how important an effect this is, and thereby give us a
better understanding of the evolution of quasars and black holes at early
epochs, as well as constrain models for black hole formation.

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
for the HRC in the visible filters to verify the results derived from the
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 < z pl 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 pl
z pl
0.5, ~ 720 O IILambda3727 emission-line galaxies at 0.3 pl z pl 1.68, and pg
1000 Ly-alpha emission-line galaxies at 3 pl z pl 7 with total emission line
flux f pg 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
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 9655

ACS Post-SMOV UV Contamination Monitor

A standard star field {NGC6681} is observed about once a month through all the
ACS broad band UV filters. NGC6681 hosts several UV spectro – photometric
standard stars for which accurate spectra have been {and will continue to be}
measured with STIS. The target cannot be observed for three months from mid
November through to mid February, so the standard star GRW+70 will be observed
twice in its stead. This programme continues the UV sensitivity monitoring
campaign {ACS SMOV proposal 9010} of the HRC and SBC after the end of the SMOV
period. An SBC dark current measurement is taken as the last exposure of each
SBC sequence.

ACS 9463

Are OH/IR stars the youngest post-AGB stars? An ACS SNAPshot imaging survey

Essentially all well-characterized preplanetary nebulae {PPNs}– objects in
transition between the AGB and planetary nebula evolutionary phases – are
bipolar, whereas the mass-loss envelopes of AGB stars are strikingly spherical.
In order to understand the processes leading to bipolar mass-ejection, we need
to know at what stage of stellar evolution does bipolarity in the mass-loss
first manifest itself? We have recently hypothesized that most OH/IR stars
{evolved mass- losing stars with OH maser emission} are very young PPNe. We
propose an ACS/SNAPshot imaging survey of a large, morphologically unbiased
sample of these objects, selected using their IRAS 12-to-25micron colors. Our
ground-based imaging study of OH/IR stars has revealed a few compact bipolar
objects, supporting our hypothesis. However since most objects remain
unresolved, HST observations are needed to determine how and when the bipolar
geometry asserts itself. Our complementary program of interferometric
mapping of
the OH maser emission in our sources is yielding kinematic information with
spatial resolution comparable to that in the HST images. The HST/radio data
provide crucial input for theories of post-AGB stellar evolution. In addition,
these data will also indicate whether the multiple concentric rings,
“searchlight beams”, and truncated equatorial disks recently discovered with
HST in a few PPNs, are common or rare phenomena.

ACS 9673

CCD Daily Monitor

This program consists of basic tests to monitor, the read noise, the
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
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 9399

Insights into Elliptical Galaxy Formation from HST Imaging of Shell Galaxies

We propose to use ACS to carry out an imaging survey of the cores of shell
galaxies. Key to understanding several aspects of shell formation is to
determine how far in do shells exist. Photometric detection from the ground is
limited by seeing and sampling to radii of at best R ~ 10 – 15 arcsec. In
velocity maps derived from high spatial resolution long-slit and integral-field
ground-based spectra we have found shell-like features with distinct kinematics
in several shell galaxy cores {R ~ 3 – 5 arcsec ~ 1 kpc}. Hence we believe that
shells may extend further in than previously known. HST provides the spatial
resolution and sampling needed to map out shells in the pronounced surface
brightness gradients of elliptical galaxy cores. The data will allow us to
detect and map inner shells, to measure their colors, to establish their
dynamics with the help of ground-based kinematics, to compare the inner surface
brightness profiles of shell and non-shell ellipticals, and to measure the mass
and distribution of the dust. Where shells are found, combined spatial and
velocity information will establish the orbital structure of shell- producing
merger debris on the basis of data, and will allow useful checks of the models
for formation of shell systems in early-type galaxies.

ACS 9293

Massive Black Holes in Early Type Galaxies

Recently, a nearly perfect relation has been recognized between the masses of
the black holes {for 3×10^6 Msun < M_BH < 3×10^9 Msun} at the centers of
galaxies and the velocity dispersions of their bulges. However, uncertainties
over the exact slope of the correlation still remain, and it is not known if
such a relation extends to black holes of lower and higher masses. The
of small {r ~ a few hundred pc}, well defined, dust and gas disks in the nuclei
of some active elliptical galaxies opened a new avenue for measuring central
mass distributions. When ionized gas is present, a small number of high spatial
resolution {e.g. STIS} spectra are sufficient to characterize the disk dynamics
and the galaxy’s central mass {e.g., M87, M81, NGC 4374}. We propose to use
spectroscopy to measure black hole masses, using gas dynamics, in the
centers of
several brightest cluster galaxies {BCGs}, 2 nearby galaxies with low velocity
dispersions, and a number of elliptical galaxies known to harbor small nuclear
dust disks. The proposed targets encompass a wide range of black hole masses,
allowing us to fully examine the M_BH — sigma relationship. We will also
H-alpha and continuum images to fully characterize the gaseous and dust
morphology as well as stellar surface profile in the central regions.

ACS 9401

The ACS Virgo Cluster Survey

We propose the most comprehensive imaging survey to date of low-redshift,
early-type galaxies. Our goal is to exploit the exceptional imaging
of the ACS by acquiring deep images — in the SDSS g^ and z^ bandpasses
— for
163 E, S0, dE, dE, N and dS0 galaxies in Virgo, the nearest rich cluster. This
extraordinary dataset would likely constitute one of the principal legacies of
HST, and would have widespread applications for many diverse areas of
astrophysics. Our immediate scientific objectives are threefold: {1} measure
metallicities, ages and radii for the many thousands of globular clusters {GCs}
in these galaxies, and use this information to derive the protogalactic mass
spectrum of each galaxy; {2} measure the central luminosity and color
profile of
each galaxy, and use this information to carry out a completely independent
of the merging hierarchy inferred from the GCs, with the aid of N-body codes
that simulate the merger of galaxies containing massive black holes; and {3}
calibrate the z^ -band SBF method, measure Virgo’s 3-D structure, and carry out
the definitive study of the GC luminosity function’s precision as a standard
candle. Our proposed Virgo Cluster Survey will yield a database of
depth, precision and uniformity, and will enable us to study the record of
galaxy and cluster formation in a level of detail which will never be possible
with more distant systems.

SpaceRef staff editor.