Status Report

NASA Hubble Space Telescope Daily Report # 3384 (part 1)

By SpaceRef Editor
June 16, 2003
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ACS 9654

ACS photometric Stability

A spectrophotometric standard star {GRW+705824} is observed through
all ACS filters once to assess the sensitivity of the instrument. The
star is placed at the centre of the aperture, and two images are taken
through each filter. This programme is based on proposal 9020 designed
for SMOV and on programme 9563 from the interim period. All the SBC
filters {except Lyman alpha F122M} and all UV filters of the HRC are
tested as part of other programmes and are not listed here. As regards
ramp filters, only one central wavelength is tested per filter. The
exposure times have been selected to reach, on average, SNR~350 in the
central pixel for broad band filters.

ACS 9661

ACS Polarization Calibration

This proposal aims to calibrate the polarization modes most heavily
used in Cycle 11. We need L-flat observations, observations of a
polarized star and an unpolarized star, and an observation of an
extended polarized source.

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 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

ACS 9714

Hubble Heritage Observations of the Sombrero Galaxy

The Hubble Heritage Team will observe the entire Sombrero Galaxy
{M104, NGC 4594} with a 6-point ACS mosaic. A color composite image
will be released to the public via the Heritage website and an STScI
photo release.

ACS 9656

Stability of the ACS CCD: geometry, flat fielding, photometry

A moderately crowded stellar field, located ~6′ West of the centre of
the cluster 47 Tuc, is observed repeatedly {every three weeks with the
WFC, every other month with the HRC} in various filters, spending 1
orbit per epoch. Different filters will be used every time, so that
over the course of the year all filters will have been employed at
least twice. The most common filters will be checked more frequently.
The same field has been observed in the course of the SMOV phase and
the positions and magnitudes of the most prominent stars have been
accurately measured. Although the field is neither a proper
astrometric nor a proper photometric standard one, the positions and
magnitudes of the objects in it can be used to monitor any local and
large scale variations in the platescale and sensitivity of the
detectors. It should be noted that for the filters which have already
been used during the SMOV phase it will be sufficient to take one
single image, without CR-SPLIT, since the exposure time is always
short {20-30 sec} and there will be so many stars that the few of them
which are affected by cosmic rays can be discarded as outliers in the
photometry. For narrow and medium band filters not exercised on this
target in the SMOV phase, however, a baseline will have to be set.
This expenditure of time will apply to the current cycle only. At
variance with the approach used in SMOV, there is no need for large
telescope slews to place the same objects on opposite sides of the
detectors, thence allowing the programme to remain compact and
efficient. All exposure level parameters are set to their default
values, except for the amplifier gain of the WFC exposures in the
F606W band, which will be collected with the gain value of 2 for the
WFC for compatibility with the SMOV observations. The exposure time is
typically 30 seconds for the WFC, 60 sec for the HRC. No attempt will
be made to attain a predefined or the same orientation on the sky
amongst different epochs. Typically, for the WFC, five exposures will
be accommodated in one orbit. For the HRC, about 10 exposures can be
fitted within one orbit

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 capabilities 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 test 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 unprecedented 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

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.


Origin and Evolution of IR Luminous Galaxies: Are z>=1 Dusty
Starbursts and z=0 ULIRGs the Same?

Interactions and mergers involving gas-rich galaxies are the main
driving mechanism behind the luminous IR galaxy phenomenon. However it
is dangerous to extrapolate this model directly to high redshifts
because massive spiral progenitors may have been relatively uncommon
at earlier epochs. Mergers and interactions involving less massive but
more gas-rich progenitors may have occurred instead. We propose to
test this hypothesis directly by imaging 12 FIR-selected, dusty
starbursts at z~1 at sub-kpc resolution afforded by HST in the rest
frame B and I {observed I and H} bands using ACS and NICMOS. While
studying higher redshift systems is clearly desirable, band-shifting
and surface brightness dimming makes the investigations of tidal
features and the nature of progenitors possible only out to z~ 1
{Hibbard & Vacca 1997}. From the morphologies, surface brightnesses,
and color distribution, we will determine the physical status of the
starburst hosts, the history of tidal interactions/mergers, and the
nature of the progenitors. We will also test for the presence of
hidden AGNs and for enhanced galaxy number density. Our 12 target
galaxies form a complete sample of known ultraluminous and
hyperluminous galaxies at 0.7<z<1.4 and represent the most distant and
the best statistical set for investigating the nature and roles played
by tidal interactions and mergers in the dusty starburst phenomenon at
high redshift.

SpaceRef staff editor.