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 z<3. 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 z>5. 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 z>3 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 z>6 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 are: (1) Detect Lya

in ~100 galaxies with z>5.6 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 0.5<z<1.8 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

0.5<z<2.2; 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

6.5<z<8. 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.