Status Report

NASA Hubble Space Telescope Daily Report # 3774

By SpaceRef Editor
January 12, 2005
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HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT        # 3774



ACS/HRC 10204

Evolution of Light Echoes of SN 1993J

SN 1993J is the nearest SN in the last decade, and only one of seven
objects to produce confirmed light echoes. Our analyses of archival
HST/WFPC2 data revealed that the SN has illuminated at least two
light-echo structures in the galaxy M81. Those echoes appear to define
two sheets of dust, located roughly 260 ly and 770 ly in front of the
SN, which are the first, and most efficient, 3-D probes of the ISM in
M81. The echoes not only reveal the ISM’s structure, but also
constrain the density, composition and grain-size of its dust. Echoes
are transient events, and as they change on timescales shorter than a
year, continued monitoring will reveal new illuminated material,
tracing interstellar and circumstellar structure. We propose a modest
and highly efficient campaign by HST to image these and yet
undiscovered echoes toward SN 1993J. Such observations will build the
first direct 3-D map of the ISM within a million cubic parsecs of
M81’s spiral arm, and may glimpse the circumstellar environment
affected by the projenitor’s mass loss. Such results probe the nature
of extragalactic dust, reveal spatio-kinematic information about the
M81’s disk, tightly constrain its internal extinction, and under the
proper circumstances, provide an independent distance measurement to
the host galaxy.

ACS/WFC 10152

A Snapshot Survey of a Complete Sample of X-ray Luminous Galaxy
Clusters from Redshift 0.3 to 0.7

We propose a public, uniform imaging survey of a well-studied,
complete, and homogeneous sample of X-ray clusters. The sample of 73
clusters spans the redshift range between 0.3-0.7. The samples spans
almost 2 orders of magnitude of X-ray luminosity, where half of the
sample has X-ray luminosities greater than 10^44 erg/s {0.5-2.0 keV}.
These snapshots will be used to obtain a fair census of the morphology
of cluster galaxies in the cores of clusters, to detect radial and
tangential arc candidates, to detect optical jet candidates, and to
provide an approximate estimate of the shear signal of the clusters
themselves, and potentially an assessment of the contribution of large
scale structure to lensing shear.

ACS/WFC 10181

ACS/NICMOS Imaging of Bright Lyman Break Galaxy Candidates from SDSS

The recent surprising discovery of six unusually bright {r~20 mag}
Lyman break galaxy {LBG} candidates with z=2.45-2.80 in the Sloan
Digital Sky Survey {SDSS} raises a number of questions that only HST
can address. Specifically, what is the true nature of these objects,
and what role if any is played by gravitational lensing? We propose to
use the superior resolution and sensitivity of ACS and NICMOS to
obtain deep images of these objects and their environments. Compared
to SDSS images, HST will allow us to determine their morphologies
{extended, point-source, or lensed}, the appearance of their
environments {rich or poor}, and to detect any faint foreground groups
or clusters that might be responsible for lensing these objects. All
outcomes would be intriguing. If the objects are lensed, it increases
from 1 {MS1512-cB58} to 7 the number of normal LBGs bright enough to
study individually. If they are instead unlensed point sources, they
will represent a new class of previously unidentified absorption-line
quasars. Finally, if they are unlensed and extended star-forming
galaxies, they are at least 4mag brighter than L_* LBGs, thus making
them the most luminous star-forming objects yet seen, representing a
heretofore unknown extreme population of objects.

ACS/WFC 10210

Groups of Dwarf Galaxies: Pools of Mostly Dark Matter?

Within 5 Mpc, there are 6 groups with well-known luminous galaxies but
there also appears to be a comparable number of groups containing only
dwarfs. If these dwarf entities are truly bound then M/L values are an
order of magnitude higher than values found for groups with luminous
spiral galaxies. There are theoretical reasons to anticipate that low
mass halos may frequently be mostly dark. The dynamical influence of
low mass halos is negligible in familiar groups with luminous members.
By contrast, a study of the dynamics of `groups of dwarfs’ may provide
direct evidence of the existence of dark matter potential wells with
few baryons. The goal of the present study is to gather detailed
information on the 3-D distribution of dwarf galaxies suspected to lie
within 7 groups of dwarfs within 5 Mpc. Distances with 7% relative
accuracy can be measured with the Tip of the Giant Branch method with
ACS and integrations within 1 orbit per target.

ACS/WFC/NIC3 10195

Probing the Surroundings of a Highly Luminous Redshift 6.5 Galaxy

We propose deep images of a recently discovered galaxy at z=6.535,
which is among the most luminous Lyman-alpha emitting galaxies known
at high redshift. The brightness and rarity of this source imply that
it is associated with a high peak in the matter density distribution.
{It is the brightest Lyman alpha source in 2e5 comoving Mpc3, with a
luminosity of 6 L*.} Further objects in this peak are expected to be
visible with HST’s sensitivity. The Lyman alpha line has a large rest
frame equivalent width, with a lower bound >100 Angstroms. Such a
large equivalent width would be impossible for objects embedded in
neutral gas, and instead requires either that {a} the universe was
reionized before z=6.5 or {b} the galaxy resides in a local ionized
bubble, in which case an additional contribution to the ionizing
photon budget from presently undetected neighbors is required. With 19
orbits of ACS and NICMOS imaging, we will measure this object’s
morphology and spectral energy distribution, thus searching for either
active nuclei or old stellar populations. We will also search for
possible neighbors, which could establish the first known galaxy group
at z>6, and may provide sufficient ionizing flux to allow the escape
of the observed Lyman alpha photons in a neutral universe. If
neighbors are not found, it will lead to an upper bound on the neutral
fraction in the general IGM at z=6.5.


The Formation and Evolution of Spirals: An ACS and WFPC2 Imaging
Survey of Nearby Galaxies

Over 50% of galaxies in the local universe are spirals. Yet the star
formation histories and evolution of this crucial population remain
poorly understood. We propose to combine archival data with new
ACS/WFC and WFPC2 observations of 11 galaxies, to tackle a
comprehensive investigation of nearby spirals covering the entire
spiral sequence. The new observations will fill a serious deficiency
in HST’s legacy, and maximize the scientific return of existing HST
data. The filter combination of UBVI, and Halpha is ideal for studying
stellar populations, dust properties, and the ISM. Our immediate
scientific objectives are: {i} to use the resolved cluster
populations, both young massive clusters and ancient globular clusters
as a chronometer, to understand how spirals assembled as a function of
time; {ii} study the rapid disruption properties of young clusters;
and {iii} understand dust distributions in spirals from pc to kpc
scales. Each of these goals provides an important step towards
charting the evolution of galaxies, and an essential baseline for
interpreting the galaxy populations being surveyed in both the early
and present universe. The resolution of our survey, which exploits the
excellent imaging capabilities of HST’s two optical cameras, will
enable us to understand the record of star cluster, and galaxy
formation in a level of detail which is not possible for more distant
systems. Finally, the proposed observations will provide a key to
interpret an extensive, multiwavelength archive of space- and ground-
based data at lower spatial resolution {SPITZER, CHANDRA, GALEX,
NICMOS P alpha and H band imaging} for local spirals.

NIC1 10143

Ultracool companions to the nearest L dwarfs

We propose to conduct the most sensitive survey to date for low mass
companions to nearby L dwarfs. We will use NICMOS to image targets
drawn from a volume-complete sample of 70 L dwarfs within 20 parsecs.
The combination of infrared imaging and proximity will allow us to
search for T dwarf companions at separations as small as 1.6 AU. This
is crucial, since no ultracool binaries are currently known with
separations exceeding 15 AU. Only 10 dwarfs in this sample have
previous HST observations primarily at optical wavelengths. With the
increased sensitivity of our survey, we will provide the most
stringent test to date of brown dwarf models which envisage formation
as ejected stellar embryos. In addition, our observations will be
capable of detecting binaries with mass ratios as low as 0.3, and will
therefore also test the apparent preference for equal-mass ultracool
binaries. Finally, our observations offer the best prospect to date of
detecting companions significantly cooler than the coolest t dwarf
currently known.


NICMOS Post-SAA calibration – CR Persistence Part 1.

A new procedure proposed to alleviate the CR-persistence problem of
NICMOS. Dark frames will be obtained immediately upon exiting the SAA
contour 23, and every time a NICMOS exposure is scheduled within 50
minutes of coming out of the SAA. The darks will be obtained in
parallel in all three NICMOS Cameras. The POST-SAA darks will be
non-standard reference files available to users with a USEAFTER
date/time mark.

WFPC2 10132

UV Confirmation of New Quasar Sightlines Suitable for the Study of
Intergalactic Helium

The reionization of intergalactic helium is thought to have occurred
between redshifts of about 3 and 4. The study of HeII Lyman-alpha
absorption towards a half-dozen quasars at 2.7 < z < 3.5 demonstrates the great potential of such probes of the IGM, but the current critically-small sample limits confidence in resulting cosmological inferences. The requisite unobscured quasar sightlines to high-redshift are extremely rare, especially due to severe absorption in random intervening Lyman-limit systems, but SDSS provides hundreds of bright, new quasars at such redshifts potentially suitable for HeII studies. Our cycle 13 SNAP program proposes to verify the UV detectability of 40 new, bright, z>2.9 SDSS quasars, but with special
emphasis on extending helium studies to the highest redshift
sightlines. Our proposed approach has already proven successful, and
additional sightlines will enable follow-up spectal observations to
measure the spectrum and evolution of the ionizing background
radiation, the density of intergalactic baryons, and the epoch of
reionization of the IGM.

WFPC2 10360


This calibration proposal is the Cycle 13 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{gain 7 and gain 15}, a test for quantum efficiency in the CCDs, and a
monitor for possible buildup of contaminants on the CCD windows.


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.) None



                            SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS Gsacq                10                        10
FGS Reacq                06                         06
Update              14                         14


SpaceRef staff editor.