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Daily Report #5184



 
 
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Old September 20th 10, 04:42 PM posted to sci.astro.hubble
Cooper, Joe
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Posts: 568
Default Daily Report #5184


HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5184

PERIOD COVERED: 5am September 17 - 5am September 20, 2010 (DOY 260/09:00z-263/09:00z)

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

12416 - GSAcq(1,2,1) at 263/5:25:24z and REAcq(1,2,1) at 263/06:57:58z
and REAcq(1,2,1) at 263/08:33:54z all failed due to search radius
limit exceeded.

Observations affected, COS 3-6 Proposal ID#11728; WFC3 5-10 Proposal
ID#11700

COMPLETED OPS REQUEST:

18918-0 Uplink new FGS calibration tables @ 262/23:32z
18921-0 R/T OBAD to Correct Attitude Error @ 263/06:32z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSAcq 19 18
FGS REAcq 21 19
OBAD with Maneuver 15 15

SIGNIFICANT EVENTS:

The FGS distortion and Calibration tables were successfully uplinked
at 262/23:30z. Table dumps performed showed the expected changes for
the FGS-2R2 values being modified. The first guide star acquisition at
263/01:30z performed nominally.

FGS 12320

The Ages of Globular Clusters and the Population II Distance Scale

Globular clusters are the oldest objects in the universe whose age can
be accurately determined. The dominant error in globular cluster age
determinations is the uncertain Population II distance scale. We
propose to use FGS 1r to obtain parallaxes with an accuracy of 0.2
milliarcsecond for 9 main sequence stars with [Fe/H] -1.5. This will
determine the absolute magnitude of these stars with accuracies of
0.04 to 0.06mag. This data will be used to determine the distance to
24 metal-poor globular clusters using main sequence fitting. These
distances (with errors of 0.05 mag) will be used to determine the ages
of globular clusters using the luminosity of the subgiant branch as an
age indicator. This will yield absolute ages with an accuracy 5%,
about a factor of two improvement over current estimates. Coupled with
existing parallaxes for more metal-rich stars, we will be able to
accurately determine the age for globular clusters over a wide range
of metallicities in order to study the early formation history of the
Milky Way and provide an independent estimate of the age of the
universe.

The Hipparcos database contains only 1 star with [Fe/H] -1.4 and an
absolute magnitude error less than 0.18 mag which is suitable for use
in main sequence fitting. Previous attempts at main sequence fitting
to metal-poor globular clusters have had to rely on theoretical
calibrations of the color of the main sequence. Our HST parallax
program will remove this source of possible systematic error and yield
distances to metal-poor globular clusters which are significantly more
accurate than possible with the current parallax data. The HST
parallax data will have errors which are 10 times smaller than the
current parallax data. Using the HST parallaxes, we will obtain main
sequence fitting distances to 11 globular clusters which contain over
500 RR Lyrae stars. This will allow us to calibrate the absolute
magnitude of RR Lyrae stars, a commonly used Population II distance
indicator.

WFC3/IR 12307

A public SNAPSHOT Survey of Gamma-ray Burst Host Galaxies

We propose to conduct a public infrared survey of the host galaxies of
Swift selected gamma-ray bursts (GRBs) at z3. By obtaining deep,
diffraction limited imaging in the IR we will complete detections for
the host galaxies, and in concert with our extensive ground based
afterglow and host programmes will compile a detailed catalog of the
properties of high-z galaxies selected by GRBs. In particular these
observations will enable us to study the colours, luminosities and
morphologies of the galaxies. This in turn informs studies of the
nature of the progenitors and the role of GRBs as probes of star
formation across cosmic history. Ultimately it provides a product of
legacy value which will greatly complement further studies with next
generation facilities such as ALMA and JWST.

ACS/WFC 12292

SWELLS: Doubling the Number of Disk-dominated Edge-on Spiral Lens
Galaxies

The formation of realistic disk galaxies within the LCDM cosmology is
still largely an unsolved problem. Theory is now beginning to make
predictions for how dark matter halos respond to galaxy formation, and
for the properties of disk galaxies. Measuring the density profiles of
dark matter halos on galaxy scales is therefore a strong test for the
standard paradigm of galaxy formation, offering great potential for
discovery. However, the degeneracy between the stellar and dark matter
contributions to galaxy rotation curves remains a major obstacle.
Strong gravitational lensing, when combined with spatially resolved
kinematics and stellar population models, can solve this long-standing
problem. Unfortunately, this joint methodology could not be exploited
until recently due to the paucity of known edge-on spiral lenses. We
have developed and demonstrated an efficient technique to find exactly
these systems. During supplemental cycle-16 we discovered five new
spiral lens galaxies, suitable for rotation curve measurements. We
propose multi-color HST imaging of 16 candidates and 2
partially-imaged confirmed systems, to measure a sample of eight new
edge-on spiral lenses. This program will at least double the number of
known disk-dominated systems. This is crucial for constraining the
relative contribution of the disk, bulge and dark halo to the total
density profile.

WFC3/IR 12265

Determining the Physical Nature of a Unique Giant Lya Emitter at
z=6.595

We propose deep WFC3/IR imaging for a giant Lya emitter (LAE) with a
Keck spectroscopic redshift of z=6.595 discovered by extensive
narrow-band imaging with Subaru in the SXDS-UKIDSS/UDS field. This
remarkable object is unique in many respects including its large
stellar mass and luminous nebula which extends over 17 kpc; no
equivalent source has been found in other surveys. The nature of this
rare object is unclear. Fundamental to progress is determining the
origin of star formation in such an early massive object; if the age
of the stellar population is short we are likely witnessing a special
moment in the formation history of a massive galaxy. The heating
source for the nebula is also unclear; options include intense star
formation, the infall of cold gas onto a dark halo or shock heating
from a merger. We will take deep broad-band (F125W and F160W) images
and an intermediate-band (F098M) image which will be analyzed in
conjunction with ultra-deep IRAC 3.6 and 4.5 micron data being taken
by the Spitzer/SEDS project. These data will enable us to constrain
the star formation rate and stellar age. Moreover, the UV continuum
morphology and Lya-line distribution will be investigated for evidence
of a major merger, cold accretion, or hot bubbles associated with
outflows. We will address the physical origin of the remarkable object
observed at an epoch where massive galaxies are thought to begin their
assembly.

WFC3/UV/IR 12234

Differentiation in the Kuiper belt: a Search for Silicates on Icy
Bodies.

We currently have a large on-going program (Go Program 11644, 120
orbits) to exploit the superb stability and photometric
characteristics of HST and the broad range in wavelength coverage of
the WFC3 to make broad-band vis/IR spectral observations of a large
sample of Kuiper belt objects. Though the survey is currently only
~50% complete, the quality and unprecedented signal-to-noise of these
observations has revealed the existence of a previously undiscovered
spectral variability not explainable within our current understanding
of these objects.

A possible explanation for this variability is that with this faint
set of Kuiper belt objects, we are beginning to see the difference
between larger differentiated objects and smaller non-differentiated
objects. Its seems that the small and likely undifferentiated objects
are exhibiting silicate features that affect our photometry - features
not exhibited by the icy mantles of larger icy bodies.

We propose a small add-on survey to dramatically increase the
scientific results of our large program. The proposed observations
will use the proven capabilities of WFC3 to make broad and narrow-band
photometric observations to detect spectral features in the 1.0-1.3
micron range of a small subset of our sources. The 13 targets have
been carefully selected to cover the range of spectral variability
detected in our large program as well as sample the entire dynamical
range and physical sizes of these targets. These observations will
allow the identification of undifferentiated Kuiper belt objects by
detection of their silicate features. As a probe for differentiation,
these observations could constrain the natal locations of different
Kuiper belt classes, a constraint currently unavailable to formation
models. This small set of observations will allow the calibration of
the spectral variability seen in our large program, and drastically
enhance the scientific output of our full Cycle 17 sample.

ACS/WFC 12210

SLACS for the Masses: Extending Strong Lensing to Lower Masses and
Smaller Radii

Strong gravitational lensing provides the most accurate possible
measurement of mass in the central regions of early-type galaxies
(ETGs). We propose to continue the highly productive Sloan Lens ACS
(SLACS) Survey for strong gravitational lens galaxies by observing a
substantial fraction of 135 new ETG gravitational-lens candidates with
HST-ACS WFC F814W Snapshot imaging. The proposed target sample has
been selected from the seventh and final data release of the Sloan
Digital Sky Survey, and is designed to complement the distribution of
previously confirmed SLACS lenses in lens-galaxy mass and in the ratio
of Einstein radius to optical half-light radius. The observations we
propose will lead to a combined SLACS sample covering nearly two
decades in mass, with dense mapping of enclosed mass as a function of
radius out to the half-light radius and beyond. With this longer mass
baseline, we will extend our lensing and dynamical analysis of the
mass structure and scaling relations of ETGs to galaxies of
significantly lower mass, and directly test for a transition in
structural and dark-matter content trends at intermediate galaxy mass.
The broader mass coverage will also enable us to make a direct
connection to the structure of well-studied nearby ETGs as deduced
from dynamical modeling of their line-of-sight velocity distribution
fields. Finally, the combined sample will allow a more conclusive test
of the current SLACS result that the intrinsic scatter in ETG
mass-density structure is not significantly correlated with any other
galaxy observables. The final SLACS sample at the conclusion of this
program will comprise approximately 130 lenses with known foreground
and background redshifts, and is likely to be the largest confirmed
sample of strong-lens galaxies for many years to come.

COS/FUV 12169

The Frequency and Chemical Composition of Planetary Debris Discs
around Young White Dwarfs

Throughout the past few years, it has become increasingly clear that
the most plausible scenario to explain the metal-pollution observed in
~20% of all cool white dwarfs is accretion from rocky debris material
- suggesting that these white dwarfs may have had, or may still have
terrestial planets as well. This hypothesis is corroborated through
the infrared detection of circumstellar dust around the most heavily
polluted white dwarfs. Traditionally, the detection of metal pollution
is done in the optical using the Ca H/K lines, leading to a strong
bias against hot/young white dwarfs. Hence, most of our knowledge
about the late evolution of planetary systems is based on white dwarfs
with cooling ages 0.5Gyr. We propose an HST/COS ultraviolet
spectroscopic snapshot survey to carry out the first systematic
investigation of the fraction of metal-pollution among young
(20-100Myr) white dwarfs, probing the correlation with white dwarf
(and hence progenitor) mass, and determining the Si/H, C/H, and
potentially N/H and O/H abundance ratios of their circumstellar debris
material.

ACS/WFC 12166

A Snapshot Survey of The Most Massive Clusters of Galaxies

We propose the continuation of our highly successful HST/ACS SNAPshot
survey of a sample of 123 very X-ray luminous clusters in the redshift
range 0.3-0.7, detected and compiled by the MACS cluster survey. As
demonstrated by dedicated HST observations of the 12 most distant MACS
clusters (GO-09722) as well as by the MACS SNAPshots of an additional
25 obtained with ACS so far in Cycles 14 and 15, these systems
frequently exhibit strong gravitational lensing as well as spectacular
examples of violent galaxy evolution. A large number of additional
MACS SNAPs have since been obtained with WFPC2, leading to the
discovery of several more powerful cluster lenses. The dramatic loss,
however, of depth, field-of-view, and angular resolution compared to
ACS led to significantly reduced scientific returns, underlining the
need for ACS for this project. The proposed observations will provide
important constraints on the cluster mass distributions, on the
physical nature of ! galaxy-galaxy and galaxy-gas interactions in
cluster cores, and will yield a set of optically bright, lensed
galaxies for further 8-10m spectroscopy. For those of our targets with
existing ACS SNAPshot images, we propose SNAPshots in the WFC3 F110W
and F140W passbands to obtain colour information that will greatly
improve the secure identification of multiple-image systems and may,
in the form of F606W or F814W dropouts, lead to the lensing-enabled
discovery of very distant galaxies at z5. Acknowledging the broad
community interest in this sample (16 of the 25 targets of the
approved MCT cluster program are MACS discoveries) we waive our data
rights for these observations.

This proposal is an updated and improved version of our successful
Cycle 15 proposal of the same title. Alas, SNAP-10875 collected only
six snapshots in the F606W or F814W passbands, due to, first, a
clerical error at STScI which caused the program to be barred from
execution for four months and, ultimately, the failure of ACS. With
ACS restored, and WFC3 providing additional wavelength and redshift
leverage, we wish to resume this previously approved project.

COS/NUV/FUV 12084

G140L/1280 Internal to External Wavelength Scale

This program observes NGC330-B37 to determine the offsets between the
PSA and WCA wavelength scales (for FP-POS=3) for the new G140L/1280
mode that will be available starting in Cycle 18. The results of the
analysis of these data will be used to update the FUV wavelength
dispersion reference file.

In addition since it this the first time that this mode is used, both
on on-orbit or on the ground, we obtain also data at FP-POS=1 and 4
which inform us of the extremes of the wavelength range that can be
seen with G140L/1280.

Note that this program can only be executed after FSW changes occur
(current estimate for these FSW changes is ~Aug 2010 timeframe) since
this mode in not yet implemented.

COS/NUV/FUV 12080

COS G140L Optics Alignment and Focus

A G140L focus sweep will be performed using the B2Ia star AZV18 in the
Small Magellanic Cloud. A sequence of time-tag spectra will be
acquired through the PSA aperture (CENWAVE=1105 A), at a range of
focus settings. There will be 17 focus settings sampled, ranging from
-800 to +800 in 100-step intervals. The optimum focus will be
determined by cross-correlating prominent absorption features in the
spectra with a template high resolution STIS E140M spectrum, then
choosing the focus setting yielding the narrowest cross-correlation
profile from the sequence. This is similar to the focusing procedure
used for the G140L grating during SMOV (PID 11484, Visit 3), except
that the new focus sweep will extend to more extreme focus positions
around 0 (+/-800 instead of +/-600). The inclusion of additional focus
positions is necessary because the G140L focus curve from SMOV
(cross-correlation FWHM vs. focus position) is broad and shallow,
making it difficult to measure the minimum in the curve. After
obtaining an exposure at the most extreme positive focus position
(+800), the focus is returned to its nominal position (0). A final
spectrum is then acquired at that position, for repeatability
comparison with the earlier FOCUS=0 spectrum. After the data are
analyzed, a patchable constant SMS update of OSM1 focus for the G140L
grating will be uplinked.

WFC3/UV 12019

After the Fall: Fading AGN in Post-starburst Galaxies

We propose joint Chandra and HST observations of an extraordinary
sample of 12 massive post-starburst galaxies at z=0.4-0.8 that are in
the short-lived evolution phase a few 100 Myr after the peak of
merger-driven star formation and AGN activity. We will use the data to
measure X-ray luminosities, black hole masses, and accretion rates;
and with the accurate "clocks" provided by post-starburst stellar
populations, we will directly test theoretical models that predict a
power-law decay in the AGN light curve. We will also test whether star
formation and black hole accretion shut down in lock-step, quantify
whether the black holes transition to radiatively inefficient
accretion states, and constrain the observational signatures of black
hole mergers.

ACS/WFC 11996

CCD Daily Monitor (Part 3)

This program comprises basic tests for measuring the read noise and
dark current of the ACS WFC and for tracking the growth of hot pixels.
The recorded frames are used to create bias and dark reference images
for science data reduction and calibration. This program will be
executed four days per week (Mon, Wed, Fri, Sun) for the duration of
Cycle 17. To facilitate scheduling, this program is split into three
proposals. This proposal covers 308 orbits (19.25 weeks) from 21 June
2010 to 1 November 2010.

WFC3/IR/S/C 11929

IR Dark Current Monitor

Analyses of ground test data showed that dark current signals are more
reliably removed from science data using darks taken with the same
exposure sequences as the science data, than with a single dark
current image scaled by desired exposure time. Therefore, dark current
images must be collected using all sample sequences that will be used
in science observations. These observations will be used to monitor
changes in the dark current of the WFC3-IR channel on a day-to-day
basis, and to build calibration dark current ramps for each of the
sample sequences to be used by Gos in Cycle 17. For each sample
sequence/array size combination, a median ramp will be created and
delivered to the calibration database system (CDBS).

WFC3/UVIS/IR 11909

UVIS Hot Pixel Anneal

The on-orbit radiation environment of WFC3 will continually generate
new hot pixels. This proposal performs the procedure required for
repairing those hot pixels in the UVIS CCDs. During an anneal, the
two-stage thermo-electric cooler (TEC) is turned off and the
four-stage TEC is used as a heater to bring the UVIS CCDs up to ~20
deg. C. As a result of the CCD warmup, a majority of the hot pixels
will be fixed; previous instruments such as WFPC2 and ACS have seen
repair rates of about 80%. Internal UVIS exposures are taken before
and after each anneal, to allow an assessment of the procedure's
effectiveness in WFC3, provide a check of bias, global dark current,
and hot pixel levels, as well as support hysteresis (bowtie)
monitoring and CDBS reference file generation. One IR dark is taken
after each anneal, to provide a check of the IR detector.

WFC3/UVIS 11907

UVIS Cycle 17 Contamination Monitor

The UV throughput of WFC3 during Cycle 17 is monitored via weekly
standard star observations in a subset of key filters covering
200-600nm and F606W, F814W as controls on the red end. The data will
provide a measure of throughput levels as a function of time and
wavelength, allowing for detection of the presence of possible
contaminants.

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

The behavior of the WFC3 UVIS CCD will be monitored daily with a set
of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K
subarray biases are acquired at less frequent intervals throughout the
cycle to support subarray science observations. The internals from
this proposal, along with those from the anneal procedure (Proposal
11909), will be used to generate the necessary superbias and superdark
reference files for the calibration pipeline (CDBS).

COS/NUV 11896

NUV Spectroscopic Sensitivity Monitoring

The purpose of this proposal is to monitor sensitivity of each NUV
grating mode to detect any changes due to contamination or other
causes.

STIS/CCD 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1,
and 1x1 at gain = 4, to build up high-S/N superbiases and track the
evolution of hot columns.

STIS/CCD 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.

ACS/WFC3 11734

The Hosts of High Redshift Gamma-Ray Bursts

Gamma-ray bursts are the most luminous explosive events known, acting
as beacons to the high redshift universe. Long duration GRBs have
their origin in the collapse of massive stars and thus select star
forming galaxies across a wide range of redshift. Due to their bright
afterglows we can study the details of GRB host galaxies via
absorption spectroscopy, providing redshifts, column densities and
metallicities for galaxies far too faint to be accessible directly
with current technology. We have already obtained deep ground based
observations for many hosts and here propose ACS/WFC3 and WFC3
observations of the fields of bursts at z3 which are undetected in
deep ground based images. These observations will study the hosts in
emission, providing luminosities and morphologies and will enable the
construction of a sample of high-z galaxies with more detailed
physical properties than has ever been possible before.

WFC3/IR 11696

Infrared Survey of Star Formation Across Cosmic Time

We propose to use the unique power of WFC3 slitless spectroscopy to
measure the evolution of cosmic star formation from the end of the
reionization epoch at z6 to the close of the galaxy-building era at
z~0.3.Pure parallel observations with the grisms have proven to be
efficient for identifying line emission from galaxies across a broad
range of redshifts. The G102 grism on WFC3 was designed to extend this
capability to search for Ly-alpha emission from the first galaxies.
Using up to 250 orbits of pure parallel WFC3 spectroscopy, we will
observe about 40 deep (4-5 orbit) fields with the combination of G102
and G141, and about 20 shallow (2-3 orbit) fields with G141 alone.

Our primary science goals at the highest redshifts a (1) Detect Lya
in ~100 galaxies with z5.6 and measure the evolution of the Lya
luminosity function, independent of of cosmic variance; 2) Determine
the connection between emission line selected and continuum-break
selected galaxies at these high redshifts, and 3) Search for the
proposed signature of neutral hydrogen absorption at re-ionization. At
intermediate redshifts we will (4) Detect more than 1000 galaxies in
Halpha at 0.5z1.8 to measure the evolution of the
extinction-corrected star formation density across the peak epoch of
star formation. This is over an order-of-magnitude improvement in the
current statistics, from the NICMOS Parallel grism survey. (5) Trace
``cosmic downsizing" from 0.5z2.2; and (6) Estimate the evolution in
reddening and metallicty in star-forming galaxies and measure the
evolution of the Seyfert population. For hundreds of spectra we will
be able to measure one or even two line pair ratios -- in particular,
the Balmer decrement and [OII]/[OIII] are sensitive to gas reddening
and metallicity. As a bonus, the G102 grism offers the possibility of
detecting Lya emission at z=7-8.8.

To identify single-line Lya emitters, we will exploit the wide
0.8--1.9um wavelength coverage of the combined G102+G141 spectra. All
[OII] and [OIII] interlopers detected in G102 will be reliably
separated from true LAEs by the detection of at least one strong line
in the G141 spectrum, without the need for any ancillary data. We
waive all proprietary rights to our data and will make high-level data
products available through the ST/ECF.

WFC3/ACS/IR 11677

Is 47 Tuc Young? Measuring its White Dwarf Cooling Age and Completing
a Hubble Legacy

With this proposal we will firmly establish the age of 47 Tuc from its
cooling white dwarfs. 47 Tuc is the nearest and least reddened of the
metal-rich disk globular clusters. It is also the template used for
studying the giant branches of nearby resolved galaxies. In addition,
the age sensitive magnitude spread between the main sequence turnoff
and horizontal branch is identical for 47 Tuc, two bulge globular
clusters and the bulge field population. A precise relative age
constraint for 47 Tuc, compared to the halo clusters M4 and NGC 6397,
both of which we recently dated via white dwarf cooling, would
therefore constrain when the bulge formed relative to the old halo
globular clusters. Of particular interest is that with the higher
quality ACS data on NGC 6397, we are now capable with the technique of
white dwarf cooling of determining ages to an accuracy of +/-0.4 Gyrs
at the 95% confidence level. Ages derived from the cluster turnoff are
not currently capable of reaching this precision. The important role
that 47 Tuc plays in galaxy formation studies, and as the metal-rich
template for the globular clusters, makes the case for a white dwarf
cooling age for this metal-rich cluster compelling.

Several recent analyses have suggested that 47 Tuc is more than 2 Gyrs
younger than the Galactic halo. Others have suggested an age similar
to that of the most metal poor globular clusters. The current
situation is clearly uncertain and obviously a new approach to age
dating this important cluster is required.

With the observations of 47 Tuc, this project will complete a legacy
for HST. It will be the third globular cluster observed for white
dwarf cooling; the three covering almost the full metallicity range of
the cluster system. Unless JWST has its proposed bluer filters (700
and 900 nm) this science will not be possible perhaps for decades
until a large optical telescope is again in space. Ages for globular
clusters from the main sequence turnoff are less precise than those
from white dwarf cooling making the science with the current proposal
truly urgent.

COS/NUV/FUV 11598

How Galaxies Acquire their Gas: A Map of Multiphase Accretion and
Feedback in Gaseous Galaxy Halos

We propose to address two of the biggest open questions in galaxy
formation - how galaxies acquire their gas and how they return it to
the IGM - with a concentrated COS survey of diffuse multiphase gas in
the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal
is to establish a basic set of observational facts about the physical
state, metallicity, and kinematics of halo gas, including the sky
covering fraction of hot and cold material, the metallicity of infall
and outflow, and correlations with galaxy stellar mass, type, and
color - all as a function of impact parameter from 10 - 150 kpc.
Theory suggests that the bimodality of galaxy colors, the shape of the
luminosity function, and the mass-metallicity relation are all
influenced at a fundamental level by accretion and feedback, yet these
gas processes are poorly understood and cannot be predicted robustly
from first principles. We lack even a basic observational assessment
of the multiphase gaseous content of galaxy halos on 100 kpc scales,
and we do not know how these processes vary with galaxy properties.
This ignorance is presently one of the key impediments to
understanding galaxy formation in general. We propose to use the
high-resolution gratings G130M and G160M on the Cosmic Origins
Spectrograph to obtain sensitive column density measurements of a
comprehensive suite of multiphase ions in the spectra of 43 z 1 QSOs
lying behind 43 galaxies selected from the Sloan Digital Sky Survey.
In aggregate, these sightlines will constitute a statistically sound
map of the physical state and metallicity of gaseous halos, and
subsets of the data with cuts on galaxy mass, color, and SFR will seek
out predicted variations of gas properties with galaxy properties. Our
interpretation of these data will be aided by state-of-the-art
hydrodynamic simulations of accretion and feedback, in turn providing
information to refine and test such models. We will also use Keck,
MMT, and Magellan (as needed) to obtain optical spectra of the QSOs to
measure cold gas with Mg II, and optical spectra of the galaxies to
measure SFRs and to look for outflows. In addition to our other
science goals, these observations will help place the Milky Way's
population of multiphase, accreting High Velocity Clouds (HVCs) into a
global context by identifying analogous structures around other
galaxies. Our program is designed to make optimal use of the unique
capabilities of COS to address our science goals and also generate a
rich dataset of other absorption-line systems.

WFC3/IR 11591

Are Low-Luminosity Galaxies Responsible for Cosmic Reionization?

Our group has demonstrated that massive clusters, acting as powerful
cosmic lenses, can constrain the abundance and properties of
low-luminosity star-forming sources beyond z~6; such sources are
thought to be responsible for ending cosmic reionization. The large
magnification possible in the critical regions of well-constrained
clusters brings sources into view that lie at or beyond the limits of
conventional exposures such as the UDF. We have shown that the
combination of HST and Spitzer is particularly effective in delivering
the physical properties of these distant sources, constraining their
mass, age and past star formation history. Indirectly, we therefore
gain a valuable glimpse to yet earlier epochs. Recognizing the result
(and limitations) of blank field surveys, we propose a systematic
search through 10 lensing clusters with ACS/F814W and
WFC3/[F110W+F160W] (in conjunction with existing deep IRAC data). Our
goal is to measure with great accuracy the luminosity function at z~7
over a range of at least 3 magnitude, based on the identification of
about 50 lensed galaxies at 6.5z8. Our survey will mitigate cosmic
variance and extend the search both to lower luminosities and, by
virtue of the WFC3/IRAC combination, to higher redshift. Thanks to the
lensing amplification spectroscopic follow-up will be possible and
make our findings the most robust prior to the era of JWST and the
ELTs.


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