HST Daily Report # 3360 (part 1)

HUBBLE SPACE TELESCOPE

DAILY REPORT # 3360

PERIOD COVERED: DOYs 129-131

OBSERVATIONS SCHEDULED

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
interval.
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
including
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
cosmological
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
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 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 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
will
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 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=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.

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 AGNs 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/HRC 9379

Near Ultraviolet Imaging of Seyfert Galaxies: Understanding the
Starburst-AGN
Connection

We propose a near-UV snapshot survey of 101 Seyfert galaxies using
ACS/HRC and
the filter F330W, a configuration which is optimal to detect faint star
forming
regions around their nuclei. These images will complement optical and
near-IR
images available in the HST archive, thus providing a panchromatic atlas
of the
inner regions of active galaxies, which we will use to study the
starburst-AGN
connection. The main goals of this proposal are: {1} Determine the
frequency of
circumnuclear starbursts in Seyferts, down to levels which cannot be
observed
from the ground; {2} characterize the observational {fluxes, colors,
structure,
sizes} and intrinsic {luminosities, masses, ages, global star-formation
rate}
properties of these clusters; {3} derive the luminosity functions of
young star
clusters around the nucleus of Seyferts and compare these results with
those
from normal and starburst galaxies to determine their survival rate close
to the
AGN; {4} address questions about the relation between AGNs and
starbursts, like
the possible connection between the masses and luminosities of black
holes and
starbursts, and the implications for the evolution of the black holes and
their
host galaxy bulges. By adding UV images to the existing optical and
near-IR
ones, this project will create an extremely valuable database for
astronomers
with a broad range of scientific interests, from the properties of the
AGN to
the properties of their host galaxies.

ACS/WFC 9351

Determining Hubble’s Constant from Observations of Cepheids in the Host
Galaxy
of SN Ia 1994ae

We propose to determine the luminosity of the type Ia supernova {SN Ia}
1994ae
by observing Cepheids in the host spiral galaxy NGC 3370. Modern CCD
photometry
has yielded an extremely tight Hubble diagram for SNe Ia with a precisely
determined intercept {i.e., Delta H_0/H_0} 1 measurement of the true
Hubble
constant is still limited by the calibration. The HST calibration of all
but a
few SNe Ia observed to date is significantly compromised by the
systematics of
photographic photometry and host galaxy extinction, as well as by the
photometric uncertainties associated with WFPC2. In contrast, SN 1994ae
is one
of the very best-observed SNe Ia with CCD photometry. The exquisite B, V,
R, and
I light curves are well-sampled beginning 10 days before maximum
brightness, and
they indicate little reddening. From our supernova photometry and the
current
provisional SN Ia calibration we would find a distance of 30 +/- 2.1 Mpc,
well
within the range where ACS can accurately observe Cepheid light curves
and
distinguish Cepheids from nonvariable stars.

ACS/WFC/HRC 9445

Gravitational Microlensing in the NGC 3314A-B Galaxy Pair.

The Advanced Camera for Surveys (WFC and HRC) was used to determine the
composition of the dark matter that dominates the masses of galaxies
which
is an
important unsolved problem.

FGS 9329

The Masses and Luminosities of Population II Stars

Very little is currently known concerning the mass-luminosity relation
{MLR} of
Population II stars. However, with the advent of the Hipparcos Catalogue,
improved distances to many spectroscopic binaries known to be Pop II
systems are
now available. After surveying the literature and making reasonable
estimates of
the secondary masses, we find 13 systems whose minimum separation should
be
larger than the resolution limit of FGS1. Because of the expected
magnitude
differences and separations, it is not possible to resolve the systems
from the
ground. We therefore propose FGS observations of the sample. In
combination
with
the known spectroscopic orbits and Hipparcos distances, these
observations will
yield up to 26 precise stellar mass determinations of metal-poor stars,
if all
systems are resolved and the relative orbits are determined. A
combination of
FGS data and ground-based observations will lead to component
luminosities and
effective temperatures. This program will allow for a significantly
better
understanding of the Pop II main sequence, which in turn will lead to
better
ages and distances of the galactic globular clusters, and a Pop II MLR
will be
constructed for the first time.

HST 9382

A Large Targeted Survey for z < 1.6 Damped Lyman Alpha Lines in SDSS QSO
MgII-FeII Systems.

We have searched the first public release of SDSS QSO spectra for low-z
{z<1.65}
metal absorption lines and found over 200 large rest equivalent width
MgII-FeII
systems. Previously, we empirically showed that such systems are good
tracers of
large neutral gas columns, with ~50% being classical damped Lyman alpha
{DLA}
systems {N_HI>=2*10^20 cm^-2}. Here we propose to follow up a
well-defined
subset of 79 of them to search for DLAs with 0.47<z<1.60. Only QSOs
brighter
than g’=19 were selected. The QSO emission and DLA absorption redshifts
were
constrained to virtually eliminate data loss due to intervening Lyman
limit
absorption. Consequently, we expect to discover ~40 new DLAs, which is a
three-fold increase in this redshift interval. This will significantly
improve
our earlier low-z DLA statistical results on their incidence,
cosmological mass
density, and N_HI distribution. The results will also allow us to better
quantify the empirical DLA — metal-line correlation. With this improved
understanding, the need for follow-up UV spectroscopy will lessen and,
with the
release of the final database of SDSS QSO spectra {an ~25-fold increase},
the
number of low-z DLAs could be increased arbitrarily. Thus, the power of
the
large and statistically-sound SDSS database in combination with a proven
technique for finding low-z DLAs will, over the next few years,
essentially
solve the problem of making an accurate determination of the cosmic
evolution of
the neutral gas component down to z~0.4.

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.