HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4813

PERIOD COVERED: 5am March 17 - 5am March 18, 2009 (DOY

                           076/0900z-077/0900z)

OBSERVATIONS SCHEDULED

WFPC2 11978

Luminous and Dark Matter in Disk Galaxies from Strong Lensing and

Stellar Kinematics

The formation of realistic disk galaxies within the LCDM paradigm is

still an unsolved problem. Theory is only 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, from an observational point of view, the degeneracy

between the stellar and dark matter contributions to galaxy rotation

curves remains a major road block. Strong gravitational lensing, when

coupled to spatially-resolved kinematics and stellar population models,

can solve this long-standing problem. Unfortunately, this joint

methodology could not be exploited so far due to the paucity of known

edge-on spiral lenses. Exploiting the full SDSS-DR7 archive we have

identified a new sample of exactly these systems. We propose multi-color

HST imaging to confirm and measure a sample of twenty spiral lenses,

covering a range of bulge to disk ratios. By combining dynamical lensing

and stellar population information for this unique sample we will

deliver the first statistical constraints on halos and disk properties,

and a new stringent test of disk galaxy formation theories.

WFPC2 11986

Completing HST's Local Volume Legacy

Nearby galaxies offer one of the few laboratories within which stellar

populations can be tied to multi-wavelength observations. They are thus

essential for calibrating and interpreting key astrophysical

observables, such as broad-band luminosities, durations and energy input

from starbursts, and timescales of UV, H-alpha, and FIR emission. The

study of stellar populations in nearby galaxies requires high-resolution

observations with HST, but HST's legacy for this limited set of galaxies

remains incomplete.

As a first attempt to establish this legacy, The ACS Nearby Galaxy

Survey Treasury (ANGST) began observations in late 2006. ANGST was

designed to carry out a uniform multi-color survey of a volume-limited

sample of ~70 nearby galaxies that could be used for systematic studies

of resolved stellar populations. The resulting data provide nuanced

constraints on the processes which govern star formation and galaxy

evolution, for a well-defined population of galaxies. All photometry for

the survey has been publicly released.

However, the failure of ACS 4.5 months after ANGST began taking data led

to a drastic reduction in the planned survey. The loss is two-fold.

First, the goals of completeness and uniformity were greatly

compromised, impacting global comparison studies. Second, the variety of

observed star formation histories was reduced. Given that we have never

found two galaxies with identical star formation histories, and fully

sampling the population allows us to catch those few systems whose star

formation rates and metallicities place the strongest constraints on key

astrophysical processes.

Here we propose WFPC2 observations of all remaining galaxies within the

Local Volume (D<3.5Mpc) for which current HST observations are

insufficient for meaningful stellar population studies. We will use

these observations for research on the star formation histories of

individual galaxies and the Local Volume, detailed calibrations of star

formation rate indicators, and the durations of starbursts. We will also

make them publicly available through the ANGST archive to support future

research. The proposed observations will finally complete a lasting

legacy of HST

WFPC2 11987

The Recent Star Formation History of SINGS Galaxies

The Spitzer Legacy project SINGS provided a unique view of the current

state of star formation and dust in a sample of galaxies of all Hubble

types. This multi-wavelength view allowed the team to create current

star formation diagnostics that are independent of the dust content and

increased our understanding of the dust in galaxies. Even so, using the

SINGS data alone we can only make rough estimates of the recent star

formation history of these galaxies. The lack of U-band observations

means that it is impossible to estimate the ages of young clusters. In

addition, the low resolution of the Spitzer and ground-based

observations means that what appear to be individual Spitzer sources can

actually be composed of many individual clusters with varying ages. In

this proposal we plan to address this missing area in SINGS by obtaining

high-resolution WFPC2 UBVI observations to accurately find and determine

the ages of the young stellar clusters in a subset of the SINGS

galaxies. These observations will greatly enhance the legacy value of

the SINGS observations while also directly answering questions

pertaining to star formation in galaxies.

WFPC2 11988

Searching for Intermediate Mass Black Holes in Globular Clusters via

Proper Motions

The unambiguous detection of an intermediate mas black hole (IMBH) in a

globular star cluster would be a major achievement for the Hubble Space

Telescope. It is critical to know whether or not IMBHs exist in the

centers of clusters in order to understand the dynamical evolution of

dense stellar systems. Also, n IMBH detection would prove the existence

of BHs in an entirely new mass range. Observationally, the search has

been hampered by the low number of stars with known velocities in the

central few arcseconds. This limits measurements of the stellar velocity

dispersion in the region where the gravitational influence of any IMBH

would be felt. Existing IMBH claims i the literature have all been

called into question, and have all been based on line-of-sight

velocities from spectroscopy. In cycle 13, we obtained ACS/HRC

observations for 5 nearby Galactic globular clusters for a new proper

motion study. Here, we request WFPC2/PC observations of these clusters,

all of which are observable in Feb-May 2009. This 4 year baseline will

allow us to measure the proper motions of stars into the very center of

each cluster, and either detect or place firm constraints on the

presence of an IMBH. In addition, we will determine whether or not the

clusters rotate or show any anisotropy in their motions. Our small (<75

orbit) program meets the criteria of addressing high impact science

(IMBH detection) using innovative methods (proper motions).

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)

HSTARS:

11728 - REAcq(1,2,1) at 076/10:03:45 failed to RGA hold due to scan step

           limit exceeded on FGS 1 at 10:09:34.

           Observations affected: WFPC 63, Proposal ID# 11978.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                       SCHEDULED      SUCCESSFUL

FGS GSAcq               04                  04               

FGS REAcq               09                  08               

OBAD with Maneuver 20                  20              

SIGNIFICANT EVENTS: (None)