Status Report

NASA Hubble Space Telescope Daily Report # 4634

By SpaceRef Editor
June 19, 2008
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NASA Hubble Space Telescope Daily Report # 4634


Continuing to collect World Class Science

PERIOD COVERED: 5am June 17 – 5am June 18, 2008 (DOY 169/0900z-170/0900z)


ACS/SBC 11225

The Wavelength Dependence of Accretion Disk Structure

We can now routinely measure the size of quasar accretion disks using gravitational microlensing of lensed quasars. The next step to testing accretion disk models is to measure the size of accretion disks as a function of wavelength, particularly at the UV and X-ray wavelengths that should probe the inner, strong gravity regime. Here we focus on two four-image quasar lenses that already have optical {R band} and X-ray size measurements using microlensing. We will combine the HST observations with ground-based monitoring to measure the disk size as a function of wavelength from the near-IR to the UV. We require HST to measure the image flux ratios in the ultraviolet continuum near the Lyman limit of the quasars. The selected targets have estimated black hole masses that differ by an order of magnitude, and we should find wavelength scalings for the two systems that are very different because the Blue/UV wavelengths should correspond to parts of the disk near the inner edge for the high mass system but not in the low mass system. The results will be modeled using a combination of simple thin disk models and complete relativistic disk models. While requiring only 18 orbits, success for one system requires observations in both Cycles 16 and 17.

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.

NIC2 11143

NICMOS Imaging of Submillimeter Galaxies with CO and PAH Redshifts

We propose to obtain F110W and F160W imaging of 10 z~2.4 submillimeter galaxies {SMGs} whose optical redshifts have been confirmed by the detection of millimeter CO and/or mid- infrared PAH emission. With the 4000A break falling within/between the two imaging filters, we will be able to study these sources’ spatially resolved stellar populations {modulo extinction} in the rest-frame optical. SMGs’ large luminosities appear to be due largely to merger-triggered starbursts; high-resolution NICMOS imaging will help us understand the stellar masses, mass ratios, and other properties of the merger progenitors, valuable information in the effort to model the mass assembly history of the universe.

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 11022

WFPC2 Cycle 15 Decontaminations and Associated Observations

This proposal is for the WFPC2 decons. Also included are instrument monitors tied to decons: photometric stability check, focus monitor, pre- and post-decon internals {bias, intflats, kspots, & darks}, UV throughput check, VISFLAT sweep, and internal UV flat check.

WFPC2 11235

HST NICMOS Survey of the Nuclear Regions of Luminous Infrared Galaxies in the Local Universe

At luminosities above 10^11.4 L_sun, the space density of far-infrared selected galaxies exceeds that of optically selected galaxies. These `luminous infrared galaxies’ {LIRGs} are primarily interacting or merging disk galaxies undergoing enhanced star formation and Active Galactic Nuclei {AGN} activity, possibly triggered as the objects transform into massive S0 and elliptical merger remnants. We propose NICMOS NIC2 imaging of the nuclear regions of a complete sample of 88 L_IR > 10^11.4 L_sun luminous infrared galaxies in the IRAS Revised Bright Galaxy Sample {RBGS: i.e., 60 micron flux density > 5.24 Jy}. This sample is ideal not only in its completeness and sample size, but also in the proximity and brightness of the galaxies. The superb sensitivity and resolution of NICMOS NIC2 on HST enables a unique opportunity to study the detailed structure of the nuclear regions, where dust obscuration may mask star clusters, AGN and additional nuclei from optical view, with a resolution significantly higher than possible with Spitzer IRAC. This survey thus provides a crucial component to our study of the dynamics and evolution of IR galaxies presently underway with Wide-Field, HST ACS/WFC and Spitzer IRAC observations of these 88 galaxies. Imaging will be done with the F160W filter {H-band} to examine as a function of both luminosity and merger stage {i} the luminosity and distribution of embedded star clusters, {ii} the presence of optically obscured AGN and nuclei, {iii} the correlation between the distribution of 1.6 micron emission and the mid- IR emission as detected by Spitzer IRAC, {iv} the evidence of bars or bridges that may funnel fuel into the nuclear region, and {v} the ages of star clusters for which photometry is available via ACS/WFC observations. The NICMOS data, combined with the HST ACS, Spitzer, and GALEX observations of this sample, will result in the most comprehensive study of merging and interacting galaxies to date.


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.


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

HSTARS: (None)



                         SCHEDULED      SUCCESSFUL

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


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