Status Report

NASA Hubble Space Telescope Daily Report # 3428 (part 1)

By SpaceRef Editor
August 18, 2003
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HUBBLE SPACE TELESCOPE

DAILY REPORT # 3428

PERIOD COVERED: DOYs 227-229

OBSERVATIONS SCHEDULED

ACS 9760

ACS Imaging of the Gemini Deep Deep Survey Fields: Galaxy Assembly at z =
1.5

We are presently carrying out the deepest redshift survey ever undertaken
{the
Gemini Deep Deep Survey}. Spectra of extraordinary quality have been taken
in
order to obtain redshifts in the so-called "redshift desert" at 1<z<2. This
redshift range corresponds to the epoch of peak galaxy formation. In this
proposal we request 40 orbits of ACS imaging to determine the morphologies
of
100-120 candidate early-type galaxies with known redshifts in our survey
fields.
We seek to determine if these systems are indeed elliptical galaxies and to
link
their morphological states to their spectroscopically determined ages,
recent
star-formation histories, and to the evolving global stellar mass function
at
the peak epoch of galaxy assembly.

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 9675

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 9984

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 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/HRC 9853

A Search for Young Binary Brown Dwarfs: Constraining Formation Scenarios and
Masses Through Multiplicity

We propose to use the Advanced Camera for Surveys / High Resolution Camera
to
conduct a direct imaging multiplicity survey of 34 young brown dwarfs in the
nearest regions of recent star formation, the T association Taurus-Auriga
and
the OB association Upper Scorpius. The determined multiplicity fraction, the
separation distribution, and the mass ratio distribution will offer
stringent
observational constraints on proposed brown dwarf formation scenarios.
Moreover,
the small semi-major axes of known field and open cluster brown dwarf
binaries
suggest the exciting possibility of our identifying several very close
binaries
{< 15 AU}. Continued monitoring of these systems would yield, on a decade
timescale, the first dynamical mass estimates of T Tauri brown dwarfs. With
masses intermediate between those of stars and planets, brown dwarfs offer
our
best hope of relating the reasonably well understood processes of star
formation
to the less well understood processes of planet formation.

ACS/HRC 9896

A Survey of Extinction Curves to Redshift z=1

The effects of dust are crucial to the study of galaxies {through models of
galaxy evolution and star formation rates/histories}, cosmology {e.g.,
through
its effects on SNe Ia fluxes}, and the interpretation of gamma-ray burst
afterglows. ?However, classical methods for obtaining precise extinction
curves
cannot be applied outside the Local Group. Recently, we demonstrated that
gravitational lenses can be used to measure extinction curves at
intermediate
redshifts with high accuracy. We propose a survey of the extinction curves
in 6
lens galaxies known to contain dust, to study the evolution of dust
properties
in galaxies out to z=1. ?We will obtain multi-wavelength photometry {6
filters
from 8140 A to 2550 A} of each system to {1} construct non-parametric
extinction
curves which overlap the 2175 A feature, {2} measure R{V} to a 2-sigma
accuracy
better than 0.5 for parametric models of Galactic dust, and {3} discriminate
between Galactic and SMC extinction curves to better than 2-sigma accuracy.
The
compact angular size of the lens systems {1-2 arcsec} and the need for
near-UV
images means that HST is required to make the measurements.

ACS/HRC 9974

Mid-Ultraviolet Spectral Templates for Old Stellar Systems

We propose a three-year program to provide both observational and
theoretical
mid-ultraviolet {2300A — 3100A} spectral templates for interpreting the
age and
metallicity of globular clusters and elliptical galaxies from spectra of
their
integrated light. The mid-UV is the region most directly influenced by
stellar
age, and is observed directly in optical and infrared studies of
high-redshift
quiescent systems. The reliability of age and metallicity determinations
remains
questionable until non-solar metallicities and abundance ratios are
considered,
and stars spanning the color-magnitude diagram are included, as we propose
here.
With archival HST STIS spectra we have improved the list of mid-UV atomic
line
parameters, then calculated spectra from first principles which match
observed
spectra of standard stars up to one- fourth solar metallicity. We will
extend
both observations and calculations to stars of solar metallicity and
beyond, and
to those in short-lived stages hotter than the main-sequence turnoff, stars
not
currently well-represented in empirical libraries. The necessary line-list
improvements will come from new high-resolution mid-UV spectra of nine field
stars. A key application of the results of this program will be to the old
systems now being discovered as `Extremely Red Objects’ at high redshifts.
Reliable age-dating of these places constraints on the epoch when large
structures first formed in the universe.

ACS/WFC 9830

A New Member of the Local Group?

An August 2002 detection at 21-cm of a previously undetected low surface
brightness galaxy yielded a radial velocity of -360 km/s. As the galaxy is
located in the opposite part of the sky as the Virgo cluster, its seems
quite
likely that this velocity places it squarely in the Local Group {LG}. The
characteristics of this galaxy, if its at a distance of 1-2 Mpc, are such
that
it easily could have escaped detection from previous searches. Its optical
surface brightness is low and its integrated blue magnitude would lie in the
range -6.5 to -8.0. The total H I mass is less than 3 x 10^5 solar masses.
The H
I profile is relatively low S/N and distorted, with a signal that is spread
out
over about 80 km/s. much larger than the internal velocity dispersion of the
galaxy. This is likely the result of an interaction {most probably with
M31}.
With the efficiency of the ACS, we can easily detect the TRGB population in
this
object using V and I observations in 2 orbits. The goal here is to provide
confirming evidence that this object is indeed a member of the LG by
obtaining
its distance via the now well calibrated TRGB method using V-I as the filter
system. If indeed in the LG {which seems likely} it would also represent a
new
kind of dwarf galaxy as its considerably more compact than other LG dwarfs
of
similar absolute magnitude.

ACS/WFC 9891

A snapshot survey of rich stellar clusters in the Large and Small Magellanic
Clouds

Rich stellar clusters are vital to a wide variety of astrophysical research,
from stellar evolution studies to the formation and evolution of galaxies.
In
this context, it is important to understand how rich star clusters form and
evolve. The cluster systems in the LMC and SMC are particularly important in
achieving this, because they are the only systems which contain clusters at
all
stages of evolution while being close enough to be studied as fully resolved
stellar populations – although in general this requires the capabilities of
HST.
We have recently investigated the structural evolution of LMC and SMC
clusters
using archival WFPC2 data, and demonstrated a dramatic trend in the sizes of
these clusters with age. We have shown that this trend likely represents
genuine
structural evolution in these clusters, although it is not clear whether we
are
observing a dynamical process or the signature of changing formation
conditions.
This result has implications for all astronomical research involving massive
stellar clusters. To develop this work further requires the extension of
our two
samples, so that they are statistically quantifiable. This will allow a
number
of key questions regarding the structural evolution trend to be answered. We
propose a two-colour ACS/WFC SNAP survey of rich Magellanic Cloud clusters
to
achieve this aim. The unique resolution and sensitivity of ACS/WFC is
required
for success, because of the crowded nature of the targets. The SNAP data
will
have a large number of additional applications, both to globular cluster and
Magellanic Cloud research.

ACS/WFC 9902

The Evolution of the Host Galaxies of Radio-Quiet Quasars

Study of the host galaxies and environments of high redshift AGN is proving
a
valuable probe of current theories of how galaxies form and evolve. Results
from
our NICMOS imaging program have indicated that the hosts of z ~ 2 — 3 faint
radio-quiet quasars {RQQ} have luminosities only around local L*, making
them
similar to Lyman-break field galaxies at the same redshifts, and to the
low-z
hosts RQQ hosts. This is roughly consistent with theoretical predictions of
Kauffmann & Haehnelt {2000} for the hierarchical buildup of galaxy hosts and
their relation to their resident supermassive black holes. The luminosity
of the
AGN in these RQQ is key to understanding this relationship, however, and we
are
making a comprehensive archival HST imaging study of the hosts of RQQs from
low
to high z at a range of nuclear luminosities. At intermediate z, however,
there
are no studies of the hosts of RQQs in the faint luminosity range that
represents the bulk of the quasar population. In the present proposal, we
request imaging at the same rest-wavelengths as our high-z sample of the
hosts
of 10 similarly luminous RQQs at z ~ 0.9. These data will fill in an
important
part of the parameter space defined by quasar luminosity and redshift.
Combined
with existing HST data they will allow us to trace the evolution of the
hosts of
RQQ and that of the relationship between quasar luminosity and host galaxy
luminosity.

ACS/WFC/HRC 9908

Evolution of Scaling Relations of Field Spiral Galaxies at Intermediate
Redshift

We seek imaging of the William Herschel Deep Field {WHDF} with the ACS to
primarily determine morphological and structural parameters of a sample of
94
late-type galaxies brighter than R=23 with redshifts up to z=1. We already
obtained spectra of the galaxies at ESO’s VLT from which spatially resolved
rotation curves are derived. Only the combined VLT and ACS data allows us
the
construction of the Tully-Fisher Relation {TFR} at intermediate redshift.
Together with 77 galaxies from the FORS Deep Field {FDF}, for which we
already
have ACS determined structural parameters, we will have the hitherto largest
kinematic sample to investigate significantly the evolution of the TFR and
the
Fundamental Plane of spiral galaxies. The additional WHDF galaxies populate
mainly both ends of the TFR {i.e. are slow rotators or bright early-type
giants}
being indispensable for the verification of an evolving slope as suggested
by
the FDF sample. Such a difference in the luminosity and mass evolution
between
dwarf and giant galaxies is a strong constraint to current theories of
galaxy
formation and evolution. The ACS imaging of the WHDF will boost its
scientific
impact also with other investigations like the study of the Fundamental
Plane of
intermediate redshift field elliptical galaxies, the study of the size and
type
evolution of an even larger sample of galaxies and the study of
galaxy-galaxy
lensing.

SpaceRef staff editor.