NASA Hubble Space Telescope Daily Report # 4474

Notice: Due to the conversion of some ACS WFC or HRC observations into WFPC2, or NICMOS observations after the loss of ACS CCD science capability in January, there may be an occasional discrepancy between a proposal’s listed (and correct) instrument usage and the abstract that follows it.

HUBBLE SPACE TELESCOPE DAILY REPORT # 4474

– Continuing to collect World Class Science

PERIOD COVERED: UT October 23, 2007 (DOY 296)

OBSERVATIONS SCHEDULED

WFPC2 10795

The Largest Galaxies in the Local Universe: New Light on Disk Galaxy Formation?

In the standard scenario of disk galaxy formation in a hierarchical Universe, large disks form late via the accretion of either hot or cold gas. Direct observational evidence for such late accretion-driven disk formation has not been forthcoming. In this proposal, we describe the discovery of a rare new type of galaxy that may be examples of massive disks in the process of assembly. We have identified a sample of three such galaxies selected from the SDSS DR4. They are extremely large {diameters over 100 kpc} and highly luminous systems with amorphous structures {no obvious spiral arms or bulges}. They are larger than the largest normal spirals in the survey, and have significantly bluer colors, lower metallicities, lower dust extinctions, higher UV luminosities and higher total star formation rates than the most massive ordinary spirals. We request HST images in the rest-frame near-UV and red to provide detailed maps of the underlying structure of these galaxies as well as the distribution of the young stars. The interstellar medium of these galaxies is evidently quite different from that of normal large spirals and starburst galaxies and they may be experiencing a different mode of star formation. We believe they are worthy of further investigation with the high-resolution imaging capabilities of HST.

FGS 11211

An Astrometric Calibration of Population II Distance Indicators

In 2002 HST produced a highly precise parallax for RR Lyrae. That measurement resulted in an absolute magnitude, M{V}=3D 0.61+/-0.11, a useful result, judged by the over ten refereed citations each year since. It is, however, unsatisfactory to have the direct, parallax-based, distance scale of Population II variables based on a single star. We propose, therefore, to obtain the parallaxes of four additional RR Lyrae stars and two Population II Cepheids, or W Vir stars. The Population II Cepheids lie with the RR Lyrae stars on a common K-band Period-Luminosity relation. Using these parallaxes to inform that relationship, we anticipate a zero-point error of 0.04 magnitude. This result should greatly strengthen confidence in the Population II distance scale and increase our understanding of RR Lyrae star and Pop II Cepheid astrophysics.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration – CR Persistence Part 5

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=3Ddate/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 DARKs. 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 11082

NICMOS Imaging of GOODS: Probing the Evolution of the Earliest Massive Galaxies, Galaxies Beyond Reionization, and the High Redshift Obscured Universe

(uses ACS/SBC and WFPC2)

Deep near-infrared imaging provides the only avenue towards understanding a host of astrophysical problems, including: finding galaxies and AGN at z > 7, the evolution of the most massive galaxies, the triggering of star formation in dusty galaxies, and revealing properties of obscured AGN. As such, we propose to observe 60 selected areas of the GOODS North and South fields with NICMOS Camera 3 in the F160W band pointed at known massive M > 10^11 M_0 galaxies at z > 2 discovered through deep Spitzer imaging. The depth we will reach {26.5 AB at 5 sigma} in H_160 allows us to study the internal properties of these galaxies, including their sizes and morphologies, and to understand how scaling relations such as the Kormendy relationship evolved. Although NIC3 is out of focus and undersampled, it is currently our best opportunity to study these galaxies, while also sampling enough area to perform a general NIR survey 1/3 the size of an ACS GOODS field. These data will be a significant resource, invaluable for many other science goals, including discovering high redshift galaxies at z > 7, the evolution of galaxies onto the Hubble sequence, as well as examining obscured AGN and dusty star formation at z > 1.5. The GOODS fields are the natural location for HST to perform a deep NICMOS imaging program, as extensive data from space and ground based observatories such as Chandra, GALEX, Spitzer, NOAO, Keck, Subaru, VLT, JCMT, and the VLA are currently available for these regions. Deep high-resolution near-infrared observations are the one missing ingredient to this survey, filling in an important gap to create the deepest, largest, and most uniform data set for studying the faint and distant universe. The importance of these images will increase with time as new facilities come on line, most notably WFC3 and ALMA, and for the planning of future JWST observations.

WFPC2 11126

Resolving the Smallest Galaxies

An order of magnitude more dwarf galaxies are expected to inhabit the Local Group, based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in environments ranging from the field to rich clusters, with evidence emerging that lower density regions contain fewer dwarfs per giant than higher density regions, in further contrast to model predictions. One possible explanation for this involves the effects of reionization on the forming galaxies and naturally explains both the dearth of dwarf galaxies and the apparent environmental dependence. However, before such theories can be fully tested, we require a better understanding of the distribution of dwarf galaxies. Currently, there is no complete census of the faintest dwarf galaxies in any environment. The discovery of the smallest and faintest dwarfs is hampered by the limitations in detecting such faint and low surface brightness galaxies, and this is compounded by the great difficulty in determining accurate distances to, or ascertaining group membership for, such faint objects. The M81 group provides a unique means for establishing membership for galaxies in a low density region complete to magnitudes as faint as M_R ~ -7. With a distance modulus of 27.8, the tip of the red giant branch {TRGB} appears at I ~ 24, just within the reach of ground based surveys. We currently have surveyed a 30 square degree region around M81 with the CFHT/Megacam. From these images we have detected 15 new candidate dwarf galaxies. We propose to use the HST with WFPC2 to image these 15 galaxies in F606W and F814W bands in order to construct a color-magnitude diagram down to I =3D 25.5 from which to measure =
accurate TRGB distances to these candidate galaxies and determine star formation and metallicity histories. The overall project will provide a survey of the dwarf galaxies in the M81 group environment with unprecedented completeness to a limit of M_R < -7.

WFPC2 11194

Beyond the Bullet: Direct Detection of Dark Matter in Merging Galaxy Clusters

Our comparison of the distribution of baryons {stars and gas} and mass {from weak lensing} in the “Bullet” Cluster has recently yielded concrete evidence for dark matter independent of basic assumptions regarding the nature of the gravitational force. The one incomplete aspect of the argument relates to potential, although highly unlikely, coincidences {special alignments along the line of sight, and/or fortuitous canceling in non-standard gravitational models} that can always be invoked against results derived from the study of one object. Therefore, we propose to complete this line of investigations by increasing the size of our sample with observations of an additional cluster. Here we propose to obtain HST WFPC2 imaging mosaics around the cores of the cluster to detect at high significance if the weak gravitational lensing mass peaks are routinely displaced from the X-ray plasma clouds and aligned with the galaxy concentrations in interacting clusters. With a relatively modest allocation of time, we seek to complete a significant step toward the eventual resolution of the dark matter question.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS: 11036 – ACS 779 Fold Mechanism Move was Blocked

ACS 779 Status Buffer Message (“Fold Mechanism Move was Blocked”)
was received following the failure of the REacq(2,1,2) at
296/10:41:59 (HSTAR 11035), which caused the Take Data Flag to be down
when the Fold mechanism move to the SBC position was commanded. Flight
Software Error Count (JERRCNT) incremented to 31. OPS Note 1645-3 executed
to change JERRCNT limit to 31.

11035 – REacq(2,1,2) failed to RGA hold during LOS REacq(2,1,2) failed to RGA control during LOS. Upon
acquisition of signal at 296/11:07:19 the vehicle was not guiding and there
were no flags set. Two ACS 779 status buffer messages indicating
that take data flag was down. OBAD prior to the REacq had an RSS value of
5.69 arcseconds.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: 1645-3 – Change JERRCNT Limit @296/1142z

            SCHEDULED      SUCCESSFUL 
         
FGS GSacq    08       08
FGS REacq    07       06
OBAD with Maneuver      30       30

SIGNIFICANT EVENTS: (None)