This week on HST

HST Programs: August 24 - August 30, 2009

SMOV still under way, but science observations being made.

Selected highlights

GO 11563: Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields

The ACS optical/far-red image of the Hubble Ultra Deep Field

Galaxy evolution in the early Universe is a discipline of astronomy that has been transformed by observations with the Hubble Space Telescope. The original Hubble Deep Field, the product of 10 days observation in December 1995 of a single pointing of Wide Field Planetary Camera 2, demonstrated conclusively that galaxy formation was a far from passive process. The images revealed numerous blue disturbed and irregular systems, characteristic of star formation in galaxy collisions and mergers. Building on this initial progam, the Hubble Deep Field South (HDFS) provided matching data for a second southern field, allowing a first assessment of likely effects due to field to field cosmic variance, and the Hubble Ultra-Deep Field (UDF) probed to even fainter magitude with the Advanced Camera for Surveys (ACS). The highest redshift objects found in the UDF have redshifts approaching z~7. Pushing to larger distances, and greater ages, demands observatons at near-infrared wavelengths, as the characteristics signatures of star formation are driven further redward in the spectrum. The present program aims to extend observations beyond z~8 to z+9 or even 10 by using the WFC3-IR camera to obtain deep F850LP (Y), F105W (J) and F160W (H) images centred on the UDF and two flanking fields. Parallel observations with ACS will be used to extend the visible and red iamging data to even fainter magitudes.

GO 11788: The Architecture of Exoplanetary Systems

Artist's impression of a young planetary system

Immanuel Kant is generally credited with first proposing that the planets in the Solar System coalesced from a flat, rotating disk formed by the Solar Nebula. Direct confirmation of that process only came in the early 1990s, when millimetre-wave interferometers were able to detect molecular gas in Keplerian rotation around a handful of nearby young stars. Since then, there have been numerous other observations, including Hubble's images of proplyds (protoplanetary disks) in the Orion Cluster, and Hubble and Spitzer observations of edge-on disks in other young stars. One of the clear selling points of the Solar Nebula disk model is that it appears to offer a natural path to forming planets with coplanar orbits, matching (most of) our observations of the Solar System. On the other hand, as our knowledge of exoplanetary systems has accumulated over the last decade, it has become clear that dynamical interactions may play a very important role in the evolution of these systems. In particular, disk/planet interactions are generally regarded as responsible for the inward migration of gas giants to form hot Jupiters in <3 day period orbits. Planet-planet interactions could lead to significant changes in orbital inclination. Radial velocity planet searches are uncovering more and more multi-planet systems. This program focuses the high precision of HST's astrometric detectors, the Fine Guidance Sensors, on four of those systems. The aim is to complement the existing radial velocity measurements with sub-milliarcsecond precision astrometry, allowing determination of the true orbital paths - specifically, the relative inclination - of the low-mass objects in these systems.

GO 11732: The Temperature Profiles of Quasar Accretion Disks

The first Einstein cross, the gravitational lensed QSO, G2237+0305

Gravitational lensing is a consequence the theory of general relativity. Its importance as an astrophysical tool first became apparent with the realisation (in 1979) that the quasar pair Q0957+561 actually comprised two lensed images of the same background quasar. In the succeeding years, lensing has been used to probe the mass distributions on a variety of scales: of galaxies (primarily via multiply-imaged quasars); of galaxy clusters (arcs and arclets); and at the largest scales (weak lensing). However, lensing can also provide insight on the small-scale properties of the object being lensed. In a lensed QSO, the light from the QSO follows different paths to produce the separate images; each of those paths has a different length; consequently, flux variations in the source show up at different times in the separate images. The present program aims to take advantage of this property to probe the structure of the accretion disks surrounding the central black hole in a number of lensed QSOs. The program will combine ultraviolet observations with the WFC3/UVIS camera on HST with GALEX UV data for 5 lenses spanning as broad range of black hole masses. Studying the variation as a function of wavelength should probe the accretion disk structure, since light from the inner regions are expected to dominate at shorter wavelengths, while the outer regions dominate at longer wavelengths.