Hubble Status Report - May 2004
Following the Cycle 13 deadline on 23 January 2004, the Panel and Time Allocation Committee (TAC) met from 22 to 27 March 2004. A total of 949 proposals requesting 17 257 orbits were submitted, while the number of orbits available for Cycle 13 is the normal 3000. The acceptance rate for GO proposals was about 20%. The acceptance rate for proposals from ESA countries is 19% of the total, reflecting the high quality of European proposals which are awarded time on a strictly competitive peer-reviewed basis.
The cancellation of Servicing Mission 4 (SM4) by NASA on 16 January 2004 led to widespread public response in the media and the Administrator has asked the National Academy of Sciences to examine the options for prolonging Hubble's life. In the meantime, Hubble scientists and engineers have begun to study every option to prolong Hubble's life. Teams of scientists are looking at every possibility, from servicing Hubble without the space shuttle, perhaps robotically, to examining technical methods that could conserve the usefulness of key components. Software and techniques that will allow Hubble to operate using two gyroscopes, instead of the usual three, will be tested in the fall. Adjustments to the batteries may help lengthen their life.
In addition, NASA has issued a request for information on extending Hubble's life via robotic servicing. The request has garnered 26 proposals, focused on ways in which robotics could be used to carry out some or all of a servicing mission. Detailed studies have also been carried out on a preliminary design and feasibility of a robotic servicing mission. This may lead to a robotic servicing mission to HST in late 2007 or early 2008 that could accomplish many of the original SM4 tasks, including the installation of new instruments. In this case, Hubble operations until 2012 may be possible, providing overlap with JWST operations. In order to assure European access to an extended HST mission beyond 2006, the Memorandum of Understanding between NASA and ESA would have to be extended accordingly.
Science Highlights
The GOODS project is a major survey which used 398 orbits with ACS to cover a total area of ~0.1 square degrees in two fields, the Hubble Deep Field North (HDF-N) and the Chandra Deep Field South (CDF-S), in four bands, B, V, I, and Z. This project is part of a greater collaboration, which includes matched imaging observations with SIRTF and Chandra, plus systematic follow-up programs from the ground, including spectroscopic observations from the VLT and Keck. A number of European astronomers are involved in the project whose PI is Mauro Giavalisco.
The exquisite sensitivity, broad wavelength coverage, as well as the large area covered, have yielded the best samples to date of star-forming galaxies at very high redshfits, namely Lyman-break galaxies at z~4, 5 and 6. The team has determined the UV luminosity density, and thus the star formation density, of Lyman-break galaxies from z~3 all the way up to z~6.
There is evidence that intense "cosmic" star formation, as traced by the star-formation density of Lyman-break galaxies, was occurring very early in the cosmic evolution, at z~6 (less than 7% of the cosmic age), and that it continued with approximately the same intensity all the way to z~1 (about 43% of the cosmic age). The conclusion is that a large fraction of the current stellar mass density, possibly as much as 50%, formed very early in the cosmic history, suggesting that those early galaxies were likely progenitors of present-day spheroids. Another truly remarkable results has been the identification of a sample of 15 Type Ia supernovae at z>1. This unique sample has been used to provide the strongest constraints to date on the transition from a decelerated cosmic expansion to an accelerated one as well as the most accurate estimate so far, of SNe rates and their relation to star formation rate.