Professor of Astronomy and Astrophysics, UCSC
Astronomer, UC Observatories/Lick Observatory
Garth Illingworth's primary research interests are directed toward understanding when and how galaxies formed. To this end he has studied the structure, kinematics, and stellar populations of nearby elliptical and SO galaxies with the goal of inferring how they were built up in the distant past ("galaxy archeology")...
The Astronomy and Astrophysics Advisory Committee (AAAC) has submitted its 2008 report to Congress, NASA and NSF. The current Chair of this committee of 13 astronomers and astrophysicists is Garth Illingworth. Read more about the AAAC and download the 2004-2008 reports HERE.
R. J. Bouwens, G. D. Illingworth, M. Franx, H. Ford
We use all available deep optical and near-IR data over the two GOODS fields to search for star-forming galaxies at z>~7 and constrain the UV LF within the first 700 Myrs. Our data set includes ~23 arcmin^2 of deep NICMOS J+H imaging data and ~248 arcmin^2 of ground-based imaging (ISAAC+MOIRCS) data. In total, we find 8 z~7.4 z-dropouts in our search fields, but no z~10 J-dropout candidates. A careful consideration of a wide variety of different contaminants suggest an overall contamination level of just ~12% for our z-dropout selection. After performing detailed simulations to accurately estimate the selection volumes, we derive constraints on the UV LFs at z~7-8 and z~10. For a faint-end slope alpha=-1.74, our most likely values for M*(UV) and phi* at z~7.4 are -19.8+/-0.4 mag and 1.1_{-0.7}^{+1.7}x10^{-3} Mpc^{-3}, respectively. Our search results for z~10 J-dropouts set a 1 sigma lower limit on M*(UV) of -19.6 mag assuming that phi* and alpha are the same as their values at slightly later times. This lower limit on M*(UV) is 1.4 mag fainter than our best-fit value at z~3.8, suggesting that the UV LF has undergone substantial evolution over this time period. No evolution is ruled out at 99% confidence from z~7.4 to z~6 and at 80% confidence from z~10 to z~7.4. The inferred brightening in M*(UV) with redshift (i.e., M*(UV) = (-21.02+/-0.09) + (0.36+/-0.08) (z - 3.8)) matches the evolution expected in the halo mass function, if the mass-to-light ratio of halos is assumed to evolve as ~(1+z)^{-1}. Finally, we consider the shape of the UV LF at z>~5 and discuss the implications of the Schechter-like form of the observed LFs, particularly the abrupt cut-off at the bright end.
The House Committee on Science and Technology's Subcommittee on Space and Aeronautics hearing on "NASA's Space Science Programs: Review of Fiscal Year 2008 Budget Request and Issues" is being held on May 2, 2007. The purpose of the hearing is to examine NASA's FY08 proposed budget request and plans for space science programs including heliophysics, planetary science and astrophysics, as well as issues related to the programs. See: U.S. House Committee on Science and Technology hearing webpage.
The testimony that I was asked to prepare for this hearing can be found here: Testimony (pdf) It discusses the concerns that the AAAC discussed in its report regarding science at NASA, with particular reference to Astrophysics, and responds to questions from Chairman Udall.
The response to Questions for the Record from Chairman Udall and Ranking Member Calvert can be found here: Response to Questions for the Record. Of particular interest was the response to question 8, which asked about lifecycle mission costs for NASA missions. NASA very kindly provided the numbers in the Table in this section. The mission costs are given here: Question 8 - Mission Costs.
The Astronomy and Astrophysics Advisory Committee (AAAC) has submitted its 2007 report to Congress, NASA and NSF. The current Chair of this committee of 13 astronomers and astrophysicists is Garth Illingworth. Read more about the AAAC and download the 2004, 2005, 2006 and 2007 reports HERE.
R. J. Bouwens, G. D. Illingworth
The first 900 million years (Myr) to redshift z ~ 6 (the first seven per cent of the age of the Universe) remains largely unexplored for the formation of galaxies. Large samples of galaxies have been found at z ~ 6 (refs 1-4) but detections at earlier times are uncertain and unreliable. It is not at all clear how galaxies built up from the first stars when the Universe was about 300Myr old (z ~ 12-15) to z ~ 6, just 600Myr later. Here we report the results of a search for galaxies at z ~ 7-8, about 700Myr after the Big Bang, using the deepest near-infrared and optical images ever taken. Under conservative selection criteria we find only one candidate galaxy at z ~ 7-8, where ten would be expected if there were no evolution in the galaxy population between z ~ 7-8 and z ~ 6. Using less conservative criteria, there are four candidates, where 17 would be expected with no evolution. This demonstrates that very luminous galaxies are quite rare 700Myr after the Big Bang. The simplest explanation is that the Universe is just too young to have built up many luminous galaxies at z ~ 7-8 by the hierarchical merging of small galaxies.
R. J. Bouwens, G. D. Illingworth, J. P. Blakeslee, M. Franx
We have detected 506 i-dropouts (z~6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF parallel ACS fields (HUDF-Ps). The contamination levels are <~8% (i.e., >~92% are at z~6). With these samples, we present the most comprehensive, quantitative analyses of z~6 galaxies yet and provide optimal measures of the UV luminosity function (LF) and luminosity density at z~6, and their evolution to z~3. We redetermine the size and color evolution from z~6 to z~3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modeled systematically and quantitatively. After corrections, we derive a rest-frame continuum UV (~1350 Å) LF at z~6 that extends to M1350,AB~-17.5 (0.04L*z=3). There is strong evidence for evolution of the LF between z~6 and z~3, most likely through a brightening (0.6+/-0.2 mag) of M* (at 99.7% confidence), although the degree depends on the faint-end slope. As expected from hierarchical models, the most luminous galaxies are deficient at z~6. Density evolution (φ*) is ruled out at >99.99% confidence. Despite large changes in the LF, the luminosity density at z~6 is similar to (0.82+/-0.21 times) that at z~3. Changes in the mean UV color of galaxies from z~6 to z~3 suggest an evolution in dust content, indicating that the true evolution is substantially larger: at z~6 the star formation rate density is just ~30% of the z~3 value. Our UV LF is consistent with z~6 galaxies providing the necessary UV flux to reionize the universe.
