This week on HST

HST Programs: May 17, 2010 - May 23, 2010

Selected highlights

GO 11153: The Physical Nature and Age of Lyman Alpha Galaxies

Composite optical/X-ray/IR imaging of a high-redshift Lyman-alpha blob

Simple galaxy formation models envisage a period of extensive star formation at the earliest epochs. That activity is likely to be accompanied by substantial Lyman alpha emission, generated by ionising photons from short-lived, high-mass stars. The degree of such activity, however, and its duration remain matters of some conjecture, which can be addressed through deep, high resolution investigations of the underlying morphology of high-redshfit Lyman-alpha emitters. The higher angular resolution and increased sensitivity of HST offer significant advantages in characterising these systems. The present proposal is using HST to obtain follow-up F110W/F160W (J/H) images of 35 spectroscopically confirmed 4.5 < z < 6.5 Ly-alpha emitters. Initial observations were with NICMOS, and the progrma has moved to using WFC3 following SM4. These systems also have mid-IR data, taken using the IRAC camera on Spitzer. The observations will be used to fully characterise the spectral energy distributions and morphologies of these sources.

GO 11556: Investigations of the Pluto System

Hubble Space Telescope image of Pluto, Charon and the two new moons, Nix & Hydra

Pluto, one of the largest members of the Kuiper Belt and, until recently (still, for some), the outermost planet in the solar system, has been in the news over the last year or two. Besides the extended "planet"/"dwarf planet" debate, Pluto is the primary target of the New Horizons Mission, and Hubble observations in 2005 led to the discovery of two small moons. Together with Charon, itself only discovered in 1978, these additions make Pluto a 4-body system. Christened Nix and Hydra, the two new moons are 5,000 fainter than Pluto itself, implying diameters as small as ~30-50 km if the surface composition is similar to Pluto itself. The present program aims to better characterise these bodies through multicolour observations with WFC3. The observations are phased with a cadence that samples the different orbital periods: 6.4 days for Pluto/Charon; 24.9 days for Nix/Pluto; and 38 days for Hydra/Pluto. The goal is toidentify systematic photometric variations that might probe the rotation period, testing whether these moons are in synchronous rotation with Pluto itself.

GO 11594: A WFC3 Grism Survey for Lyman limit absorption at z=2

HRC grism image of SN 1987A, as displayed in the Hubble Legacy Archive

Grisms are optical components with finely ruled gratings that canbe introduced into the beam of an imaging camera to produce low-resolution spectra of objects within the field of view. Wide Field Camera 3 on HST has three such components: an ultraviolet grism, G280, providing spectroscopy from ~2100 to 3900 Angstroms; and two grisms, G102 and G141, for use at near-infrared wavelengths. The present program aims to use the UV grism to search for galaxies at redshifts in the range 1.8 < z < 2.5. The observations target 64 quasars, drawn from the Sloan Digital Sky Survey, that have absorption features that are characteristic of that redshift range. Those features are likely due to foreground galaxies, whose extended gaseous halos absorb light from the QSO. The grism data will used to search for sources with emission lines that indciate that they are at the appropriate redshift.

GO 11702: Search for Very High-z Galaxies with WFC3 Pure Parallel

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. Wide Field Camera 3, installed in Servicing Mission 4, is well suited to these observations, and a number of programs are in place in Cycle 17 that address these issues. Indeed, WFC3 is employed in pure parallel mode by several programs. These take advantage of other science programs, usually with COS, that involve 2-5 orbit pointings on sources at high galactic latitude. The WFC3 pointing is unplanned, since it depends on the orientation adopted for the prime observations, but 2-5 orbits of IR imaging can reach galaxies at redshifts exceeding z=7 (potentially even z~8) in high latitude fields. This is one of two such programs in the cycle 17 portfolio.