Status Report

NASA Hubble Space Telescope Daily Report #4813

By SpaceRef Editor
March 19, 2009
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Continuing to collect World Class Science

PERIOD COVERED: 5am March 17 – 5am March 18, 2009 (DOY 076/0900z-077/0900z)


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).


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


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.



                        SCHEDULED      SUCCESSFUL

FGS GSAcq               04                  04
FGS REAcq               09                  08
OBAD with Maneuver      20                  20


SpaceRef staff editor.