HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT      #4636

PERIOD COVERED: 5am June 19 - 5am June 20, 2008 (DOY 171/0900z-172/0900z)

OBSERVATIONS SCHEDULED

ACS/SBC 11215

New Sightlines for the Study of Intergalactic Helium: Dozens of

High-Confidence, UV-Bright Quasars from SDSS/GALEX

The reionization of IGM helium is thought to have occurred at redshifts

of z=3 to 4. Detailed study of HeII Lyman-alpha absorption toward a

handful of QSOs at 2.7<z<3.3 demonstrated the high potential of such IGM

probes, but the critically small sample size limits confidence in

cosmological inferences. The requisite unobscured sightlines to high-z

are extremely rare, but SDSS provides 5800, z>3.1 QSOs potentially

suitable for HeII studies. We've cross-correlated SDSS quasars with

GALEX UV sources to obtain dozens of new, high confidence, candidate

sightlines {z=3.1-4.9} potentially useful for detailed HeII studies with

HST. We propose brief, 2- orbit reconnaissance ACS SBC prism exposures

toward each of the best dozen new quasars, to definitively verify UV

flux down to HeII. Our combined SDSS/GALEX selection insures a high

confirmation rate, as the quasars are already known to be UV bright in

GALEX. Our program will provide a statistical sample of HeII sightlines

extending to high redshift, enabling future long exposure follow-up

spectra with the SBC prism, or superb quality COS or STIS spectra after

SM4. Stacks of our prism spectra will also directly yield ensemble

information. Ultimately, the new sightlines will enable confident

measures of the spectrum and evolution of the ionizing background, the

evolution of HeII opacity, the epoch of helium reionization, and the

density of IGM baryons.

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 i

mages. Each observation will need its own CRMAP, as different SAA

passages leave different imprints on the NICMOS detectors.

NIC3/WFPC2 11192

NICMOS Confirmation of Candidates of the Most Luminous Galaxies at z > 7

While the deepest pencil-beam near-IR survey suggested that the Universe

was too young to build up many luminous galaxies by z ~ 7--8 (Bouwens &

Illingworth 2006), there is also evidenc indicating the contrary. It is

now known that some galaxies with stellar masses of M>1e10 Msun were

already in place by z ~ 6--7, which strongly suggests that their

progenitors should be significantly more luminous, and hence detectable

in deep, wide-field near-IR surveys (Yan et al. 2006). As galaxies at

such a high redshift should manifest themselves as "dropouts" from the

optical, we have carried out a very wide-field, deep near-IR survey in

the GOODS fields to search for z-band dropouts as candidates of galaxies

at z > 7. In total, six promising candidates have been found in ~ 300

sq. arcmin to J_AB ~ 24.5 mag (corresponding to restframe M(UV) < -22.5

mag at z ~ 7). By contrast, the galaxy luminosity function (LF)

suggested in BI06 would predict at most 3--5 galaxies over the entire

2-pi sky at this brightness level. Here we propose to observe these

candidates with NIC3 in F110W and F160W to further investigate their

nature. If any of these candidates are indeed at z > 7, the result will

lead to a completely new picture of star formation in the early

universe. If none of our candidates are consistent with being at z > 7,

then the depth and area of our near-IR survey (from which the candidates

are drawn) will let us set a very stringent upper limit on the bright

end of the galaxy LF at those redshift. As a result, our program will

still be able to provide new clues about the processes of early galaxy

formation, such as their dust contents and their merging time scale (Yan

et al. 2006).

WFPC2 11206

At the Cradle of the Milky Way: Formation of the Most Massive Field Disk

Galaxies at z>1

We propose to obtain 2 orbit WFPC2 F814W images of a sample of the 15

most massive galaxies found at $1 < z < 1.3$. These were culled from

over 20,000 Keck spectra collected as part of DEEP and are unique among

high redshift massive galaxy samples in being kinematically selected.

Through a recent HST NICMOS-2 imaging program {GO-10532}, we have

confirmed that these galaxies have regular stellar disks, and their

emission line kinematics are not due to gradients from merging

components. These potentially very young galaxies are likely precursors

to massive local disks, assuming no further merging. The proposed WFPC2

and existing NIC-2 data provide colors, stellar masses, and ages of

bulge and disk subcomponents, to assess whether old stellar bulges and

disks are in place at that time or still being built, and constrain

their formation epochs. Finally, this sample will yield the first

statistically significant results on the $z > 1$ evolution of the

size-velocity-luminosity scaling relations, for massive galaxies at

different wavelengths, and constrain whether this evolution reflects

stellar mass growth, or passive evolution, of either bulge or disk

components.

WFPC2 11218

Snapshot Survey for Planetary Nebulae in Globular Clusters of the Local

Group

Planetary nebulae {PNe} in globular clusters {GCs} raise a number of

interesting issues related to stellar and galactic evolution. The number

of PNe known in Milky Way GCs, 4, is surprisingly low if one assumes

that all stars pass through a PN stage. However, it is likely that the

remnants of stars now evolving in Galactic GCs leave the AGB so slowly

that any ejected nebula dissipates long before the star becomes hot

enough to ionize it. Thus there should not be ANY PNe in Milky Way

GCs--but there are four! It has been suggested that these PNe are the

result of mergers of binary stars within GCs, i.e., that they are

descendants of blue stragglers. The frequency of occurrence of PNe in

external galaxies poses more questions, because it shows a range of

almost an order of magnitude. I propose a Snapshot survey aimed at

discovering PNe in the GC systems of Local Group galaxies more distant

than the Magellanic Clouds. These clusters, some of which may be much

younger than their counterparts in the Milky Way, might contain many

more PNe than those of our own galaxy. I will use the standard technique

of emission-line and continuum imaging, which easily discloses PNe.

WFPC2/NIC3/ACS/SBC 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               06                 06                           

FGS REacq               08                 08                          

OBAD with Maneuver 28                 28              

SIGNIFICANT EVENTS: (None)