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Daily Report #4511



 
 
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Old December 20th 07, 02:13 PM posted to sci.astro.hubble
Cooper, Joe
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Default Daily Report #4511

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT****** # 4511

PERIOD COVERED: UT December 19, 2007 (DOY 353)

OBSERVATIONS SCHEDULED

ACS/SBC 10907

New Sightlines for the Study of Intergalactic Helium: A Dozen
High-Confidence, UV-Bright Quasars from SDSS/GALEX

The reionization of intergalactic helium is thought to have occurred
between redshifts of about 3 and 4. Detailed study of HeII Lyman-alpha
absorption toward a handful quasars at 2.7z3.3 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 thousands
of z3.1 quasars potentially suitable for HeII studies. We have
cross-correlated SDSS quasars with GALEX UV sources to obtain a dozen
new, very high-confidence, candidate quasars/sightlines {z=3.1 to 4.1}
potentially useful for detailed HeII studies even with current HST
instruments. We propose brief, 2-orbit per target, reconnaissance
spectral exposures with the ACS SBC prism to definitively verify UV
flux down to the HeII break. Our combined SDSS/GALEX selection insures
a very high-yield of confirmations, as the quasars are already known
to be UV-bright from broadband GALEX images. The additional
sightlines, extending to very high-redshift, will directly enable
ensemble spectral stacks, as well as long exposure follow-up spectra,
at high S/N with the ACS/SBC ultraviolet prisms {or perhaps STIS or
COS later}, to confidently measure the spectrum and evolution of the
ionizing background radiation, the evolution of HeII opacity, and the
density of intergalactic baryons.

ACS/SBC WFPC2 11175

UV Imaging to Determine the Location of Residual Star Formation in
Galaxies Recently Arrived on the Red Sequence

We have identified a sample of low-redshift {z = 0.04 - 0.10} galaxies
that are candidates for recent arrival on the red sequence. They have
red optical colors indicative of old stellar populations, but blue
UV-optical colors that could indicate the presence of a small quantity
of continuing or very recent star formation. However, their spectra
lack the emission lines that characterize star-forming galaxies. We
propose to use ACS/SBC to obtain high- resolution imaging of the UV
flux in these galaxies, in order to determine the spatial distribution
of the last episode of star formation. WFPC2 imaging will provide B,
V, and I photometry to measure the main stellar light distribution of
the galaxy for comparison with the UV imaging, as well as to measure
color gradients and the distribution of interstellar dust. This
detailed morphological information will allow us to investigate the
hypothesis that these galaxies have recently stopped forming stars and
to compare the observed distribution of the last star formation with
predictions for several different mechanisms that may quench star
formation in galaxies.

WFPC2 11024

WFPC2 CYCLE 15 INTERNAL MONITOR

This calibration proposal is the Cycle 15 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
{both gain 7 and gain 15 -- to test stability of gains and bias
levels}, a test for quantum efficiency in the CCDs, and a monitor for
possible buildup of contaminants on the CCD windows. These also
provide raw data for generating annual super-bias reference files for
the calibration pipeline.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration - CR Persistence Part 6

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. The keyword 'USEAFTER=date/time' will also be added to the
header of each POST-SAA DARK frame. The keyword must be populated with
the time, in addition to the date, because HST crosses the SAA ~8
times per day so each POST-SAA DARK will need to have the appropriate
time specified, for users to identify the ones they need. Both the raw
and processed images will be archived as POST-SAA DARKSs. Generally we
expect that all NICMOS science/calibration observations started within
50 minutes of leaving an SAA will need such maps to remove the CR
persistence from the science images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

NIC3 11107

Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy
Formation in the Early Universe

We have used the ultraviolet all-sky imaging survey currently being
conducted by the Galaxy Evolution Explorer {GALEX} to identify for the
first time a rare population of low- redshift starbursts with
properties remarkably similar to high-redshift Lyman Break Galaxies
{LBGs}. These "compact UV luminous galaxies" {UVLGs} resemble LBGs in
terms of size, SFR, surface brightness, mass, metallicity, kinematics,
dust, and color. The UVLG sample offers the unique opportunity of
investigating some very important properties of LBGs that have
remained virtually inaccessible at high redshift: their morphology and
the mechanism that drives their star formation. Therefore, in Cycle 15
we have imaged 7 UVLGs using ACS in order to 1} characterize their
morphology and look for signs of interactions and mergers, and 2}
probe their star formation histories over a variety of timescales. The
images show a striking trend of small-scale mergers turning large
amounts of gas into vigorous starbursts {a process referred to as
dissipational or "wet" merging}. Here, we propose to complete our
sample of 31 LBG analogs using the ACS/SBC F150LP {FUV} and WFPC2
F606W {R} filters in order to create a statistical sample to study the
mechanism that triggers star formation in UVLGs and its implications
for the nature of LBGs. Specifically, we will 1} study the trend
between galaxy merging and SFR in UVLGs, 2} artificially redshift the
FUV images to z=1-4 and compare morphologies with those in similarly
sized samples of LBGs at the same rest-frame wavelengths in e.g.
GOODS, UDF, and COSMOS, 3} determine the presence and morphology of
significant stellar mass in "pre-burst" stars, and 4} study their
immediate environment. Together with our Spitzer {IRAC+MIPS}, GALEX,
SDSS and radio data, the HST observations will form a unique union of
data that may for the first time shed light on how the earliest major
episodes of star formation in high redshift galaxies came about. This
proposal was adapted from an ACS HRC+WFC proposal to meet the new
Cycle 16 observing constraints, and can be carried out using the
ACS/SBC and WFPC2 without compromising our original science goals.

WFPC2 10915

ACS Nearby Galaxy Survey

Existing HST observations of nearby galaxies comprise a sparse and
highly non-uniform archive, making comprehensive comparative studies
among galaxies essentially impossible. We propose to secure HST's
lasting impact on the study of nearby galaxies by undertaking a
systematic, complete, and carefully crafted imaging survey of ALL
galaxies in the Local Universe outside the Local Group. The resulting
images will allow unprecedented measurements of: {1} the star
formation history {SFH} of a 100 Mpc^3 volume of the Universe with a
time resolution of Delta[log{t}]=0.25; {2} correlations between
spatially resolved SFHs and environment; {3} the structure and
properties of thick disks and stellar halos; and {4} the color
distributions, sizes, and specific frequencies of globular and disk
clusters as a function of galaxy mass and environment. To reach these
goals, we will use a combination of wide-field tiling and pointed deep
imaging to obtain uniform data on all 72 galaxies within a
volume-limited sample extending to ~3.5 Mpc, with an extension to the
M81 group. For each galaxy, the wide-field imaging will cover out to
~1.5 times the optical radius and will reach photometric depths of at
least 2 magnitudes below the tip of the red giant branch throughout
the limits of the survey volume. One additional deep pointing per
galaxy will reach SNR~10 for red clump stars, sufficient to recover
the ancient SFH from the color-magnitude diagram. This proposal will
produce photometric information for ~100 million stars {comparable to
the number in the SDSS survey} and uniform multi- color images of half
a square degree of sky. The resulting archive will establish the
fundamental optical database for nearby galaxies, in preparation for
the shift of high- resolution imaging to the near-infrared.

WFPC2 11070

WFPC2 CYCLE 15 Standard Darks - part II

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs.

WFPC2 11202

The Structure of Early-type Galaxies: 0.1-100 Effective Radii

The structure, formation and evolution of early-type galaxies is still
largely an open problem in cosmology: how does the Universe evolve
from large linear scales dominated by dark matter to the highly
non-linear scales of galaxies, where baryons and dark matter both play
important, interacting, roles? To understand the complex physical
processes involved in their formation scenario, and why they have the
tight scaling relations that we observe today {e.g. the Fundamental
Plane}, it is critically important not only to understand their
stellar structure, but also their dark-matter distribution from the
smallest to the largest scales. Over the last three years the SLACS
collaboration has developed a toolbox to tackle these issues in a
unique and encompassing way by combining new non-parametric strong
lensing techniques, stellar dynamics, and most recently weak
gravitational lensing, with high-quality Hubble Space Telescope
imaging and VLT/Keck spectroscopic data of early-type lens systems.
This allows us to break degeneracies that are inherent to each of
these techniques separately and probe the mass structure of early-type
galaxies from 0.1 to 100 effective radii. The large dynamic range to
which lensing is sensitive allows us both to probe the clumpy
substructure of these galaxies, as well as their low-density outer
haloes. These methods have convincingly been demonstrated, by our
team, using smaller pilot-samples of SLACS lens systems with HST data.
In this proposal, we request observing time with WFPC2 and NICMOS to
observe 53 strong lens systems from SLACS, to obtain complete
multi-color imaging for each system. This would bring the total number
of SLACS lens systems to 87 with completed HST imaging and effectively
doubles the known number of galaxy-scale strong lenses. The deep HST
images enable us to fully exploit our new techniques, beat down
low-number statistics, and probe the structure and evolution of
early-type galaxies, not only with a uniform data-set an order of
magnitude larger than what is available now, but also with a fully
coherent and self-consistent methodological approach!

WFPC2/NIC3 11144

Building on the Significant NICMOS Investment in GOODS: A Bright,
Wide-Area Search for z=7 Galaxies

One of the most exciting frontiers in observational cosmology has been
to trace the buildup and evolution of galaxies from very early times.
While hierarchical theory teaches us that the star formation rate in
galaxies likely starts out small and builds up gradually, only
recently has it been possible to see evidence for this observationally
through the evolution of the LF from z~6 to z~3. Establishing that
this build up occurs from even earlier times {z~7-8} has been
difficult, however, due to the small size of current high-redshift
z~7-8 samples -- now numbering in the range of ~4-10 sources.
Expanding the size of these samples is absolutely essential, if we are
to push current studies of galaxy buildup back to even earlier times.
Fortunately, we should soon be able to do so, thanks to ~50 arcmin**2
of deep {26.9 AB mag at 5 sigma} NICMOS 1.6 micron data that will be
available over the two ACS GOODS fields as a result of one recent
180-orbit ACS backup program and a smaller program. These data will
nearly triple the deep near-IR imaging currently available and
represent a significant resource for finding and characterizing the
brightest high-redshift sources -- since high-redshift candidates can
be easily identified in these data from their red z-H colours.
Unfortunately, the red z-H colours of these candidates are not
sufficient to determine that these sources are at z=7, and it is
important also to have deep photometry at 1.1 microns. To obtain this
crucial information, we propose to follow up each of these z- H
dropouts with NICMOS at 1.1 microns to determine which are at high
redshift and thus significantly expand our sample of luminous, z=7
galaxies. Since preliminary studies indicate that these candidates
occur in only 30% of the NIC3 fields, our follow-up strategy is ~3
times as efficient as without this preselection and 9 times as
efficient as a search in a field with no pre-existing data. In total,
we expect to identify ~8 luminous z-dropouts and possibly ~2 z~10
J-dropouts as a result of this program, more than tripling the number
currently known. The increased sample sizes are important if we are to
solidify current conclusions about galaxy buildup and the evolution of
the LF from z~8. In addition to the high redshift science, these deep
1.1 micron data would have significant value for many diverse
endeavors, including {1} improving our constraints on the stellar mass
density at z~7-10 and {2} doubling the number of galaxies at z~6 for
which we can estimate dust obscuration.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.)

HSTARS: (None)

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

*********************** SCHEDULED***** SUCCESSFUL

FGS GSacq************** 09**************** 09
FGS REacq************** 06**************** 06
OBAD with Maneuver **** 30**************** 30

SIGNIFICANT EVENTS: (None)


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