HST Daily Report # 3155 (part 1)

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3155

PERIOD COVERED: DOYs 122-124

OBSERVATIONS SCHEDULED

ACS 9651

ACS CCD Flash Calibration

This activity provides a set of CCD FLASH exposure reference images for
each
current level/shutter-side/detector combination, for the pair of FLASH
LEDs on
the instrument side currently in use. It also tests the short-term
repeatability
at the shortest FLASH exposure times that are expected to be used {1.0
sec}.

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 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 9657

ACS Internal Flat Field Stability

The flat field stability and characterization obtained during the ground
calibration and SMOV phases will be tested and verified through a
sub-sample of
the filter set. Only internal exposures with the calibration lamps will
be
required.

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 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 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 9352

The Deceleration Test from Treasury Type Ia Supernovae at Redshifts 1.2
to 1.6

Type Ia supernovae {SNe Ia} provide the only direct evidence for an
accelerating
universe, an extraordinary result that needs a rigorous test. The case
for
cosmic acceleration rests on the observation that SNe Ia at z ~ 0.5 are ~
0.25
mag fainter than they would be in a universe without acceleration. A
powerful
and straightforward way to assess the reliability of the SN Ia
measurement and
the conceptual framework of its interpretation is to look for cosmic
deceleration at z >= 1. This would be a clear signature of a mixed
dark-matter
and dark-energy universe. Systematic errors in the SN Ia result
attributed to
grey dust or cosmic evolution of the SN Ia peak luminosity would not show
this
change of sign. We have demonstrated proof of this concept with a single
SN Ia,
SN 1997ff at z = 1.7, found and followed by HST. The results suggest an
early
epoch of deceleration, but this is too important a conclusion to rest on
just
one object. Here we propose to use HST for observations of six SNe Ia in
the
range 1.2 <= z <= 1.6, that will be discovered as a byproduct from proposed Treasury programs for high-latitude ACS surveys. Six objects will provide a much firmer foundation for a conclusion that touches on important questions of fundamental physics.

ACS/NICMOS 9483

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

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.

ACS/WFPC2 9481

Pure Parallel Near-UV Observations with WFPC2 within High-Latitude ACS
Survey
Fields

In anticipation of the allocation of ACS high-latitude imaging survey{s},
we
request a modification of the default pure parallel program for those
WFPC2
parallels that fall within the ACS survey field. Rather than duplicate
the red
bands which will be done much better with ACS, we propose to observe in
the
near-ultraviolet F300W filter. These data will enable study of the
rest-frame
ultraviolet morphology of galaxies at 0

NICMOS 9386

Infrared Photometry of a Statistically Significant Sample of KBOs

While the discovery rate of Kuiper Belt objects is accelerating, the
physical
study of this new region of the solar system has been slowed by a lack of
basic
astrophysical data. Photometric observations of the majority of the more
than
400 known KBOs and Centaurs are rudimentary and incomplete, particularly
in the
infrared. The multicolor optical-infrared photometry that exists for a
small
subset of KBOs often shows significant discrepancies between observations
by
different observers. Their intrinsic faintness puts them at the practical
limits
of ground-based systems. In July 2001 we began what will be the largest
uniform
sample of optical photometry of KBOs with a WFPC2 SNAPSHOT program that
will
perform accurate photometry at V, R, and I on a sample of up to 150
targets. We
seek to greatly enhance the value of this survey by obtaining J and H
photometry
on the same sample using NICMOS. Combined optical and infrared broad band
photometry is a far more powerful tool for physical studies than is
either
alone. Our sample includes objects that will be observed at thermal
infrared
wavelengths by SIRTF and will be used with those data to derive the first
accurate diameters, albedos, and surface properties for a large sample of
KBOs.