NASA Hubble Space Telescope Daily Report #4218

HUBBLE SPACE TELESCOPE DAILY REPORT # 4218

– Continuing to collect World Class Science

PERIOD COVERED: UT October 12, 2006 (DOY 285)

OBSERVATIONS SCHEDULED

ACS/WFC 10816

The Formation History of Andromeda’s Extended Metal-Poor Halo

We propose deep ACS imaging in the outer spheroid of the Andromeda galaxy, in order to measure the star formation history of its true halo. For the past 20 years, nearly all studies of the Andromeda “halo” were focused on the spheroid within 30 kpc of the galaxy’s center, a region now known to host significant substructure and populations with high metallicity and intermediate ages. However, two groups have recently discovered an extended metal-poor halo beyond 30 kpc; this population is distinct in its surface-brightness profile, abundance distribution, and kinematics. In earlier cycles, we obtained deep images of the inner spheroid {11 kpc on the minor axis}, outer disk {25 kpc on the major axis}, and giant tidal stream, yielding the complete star formation history in each field. We now propose deep ACS imaging of 4 fields bracketing this 30 kpc transition point in the spheroid, so that the inner spheroid and the extended halo populations can be disentangled, enabling a reconstruction of the star formation history in the halo. A wide age distribution in the halo, as found in the inner spheroid, would imply the halo was assembled through ongoing accretion of satellite galaxies, while a uniformly old population would be a strong indication that the halo was formed during the early rapid collapse of the Andromeda proto-galaxy.

ACS/WFC 10863

Magnifying the High-z Universe with the Bullet Cluster 1E0657-56

We propose to use the bullet cluster 1E0657-56 {z=0.296} as a gravitational telescope to conduct a pencil beam survey of the galaxy population to z=7. The cluster 1E0657-56, one of the hottest and most X-ray luminous clusters known, is a highly efficient lens with critical curves comparable in size to Abell 1689. The proposed observations will yield a high-fidelity strong+weak lensing map of the cluster core, enabling identification of lensed, high-redshift sources and also providing a precision measurement of the cluster mass {good to 5% within 350 kpc}. The mass measurement will also serve as a key input for numerical simulations designed to reconstruct the dynamical history of the cluster merger and provide a new constraint on the dark matter self-interaction cross-section. In the cluster core the requested imaging will reach {de-magnified} magnitudes comparable to the Hubble Ultra Deep Field for lensed sources, but with 2+ magnitudes of magnification facilitating spectroscopic follow-up.

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=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 10825

The Formation Epoch of Early-type Galaxies: Constraints from the Fundamental Plane at z=1.3

Field and cluster surveys both show a ~50% decrease in the number of early-type galaxies at redshifts near 1. Galaxies that have either recently transformed into early-types or undergone star formation should have younger appearing stellar populations. The resulting change in the mass-to-light ratio can be detected by the offset in the fundamental plane with redshift. We will use the fundamental plane to test whether a significant fraction of early-type galaxies have evidence of recent star formation, using a sample of ~20 z=1.3 cluster and field early-type galaxies. This is 7 times larger than the sample previously used at this redshift. We already have the high signal-to-noise 12-20 hour long Keck spectra for these galaxies we need for velocity dispersions. To use the fundamental plane, we require sizes and surface brightnesses. We propose 12 orbits of NICMOS Camera 2 imaging to measure the sizes and surface brightness distributions of these objects in a rest-frame optical passband. These data will provide high quality surface brightness profiles out two ~2 half-light radii, at wavelengths comparable to previous fundamental plane studies. When combined with our spectra, the HST data will establish the mass-to-light ratio evolution for massive early-type galaxies from the fundamental plane. We will define the epoch of last star formation for these z=1.3 galaxies, directly testing the claims of strong evolution at z=1.

NIC2 11016

NICMOS Flats: narrow and broad filters for NIC1 {+ NIC2, NIC3 in parallel}

This proposal obtains sequences of NICMOS narrow band filter flat fields for camera 1. In cameras 2 and 3, parallel observations will allow us to obtain high S/N flats for all spectral elements.

WFPC2 11028

WFPC2 Cycle 15 UV Earth Flats

Monitor flat field stability. This proposal obtains sequences of earth streak flats to improve the quality of pipeline flat fields for the WFPC2 UV filter set. These Earth flats will complement the UV earth flat data obtained during cycles 8-14.

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                08                     08 
FGS REacq                 07                    07 
OBAD with Maneuver   28                     28 

SIGNIFICANT EVENTS: (None)