Andrew Bunker

Abstract:

The quest to discover the most distant galaxies has developed rapidly in the last decade. We are now exploring redshifts of 6 and beyond, when the Universe was less than a billion years old, an epoch when the previously neutral intergalactic medium was reionized. The continuing discovery of galaxies at progressively higher and higher redshifts has been driven by the availability of large telescopes on the ground and in space, improvements in detector technology, and new search strategies. Over the past 4 years, the Lyman break technique has been shown to be effective in isolating z ≈ 6 star-forming i′-drop galaxies through spectroscopic confirmation with large ground-based telescopes (Keck, Gemini and the ESO VLTs). Analysis of the Hubble Ultra Deep Field (HUDF-the deepest images obtained so far, and likely to remain so until the James Webb Space Telescope, JWST), has enabled us to explore the faint end of the luminosity function, which may contribute the bulk of the total star formation. The discovery of this i′-drop galaxy population has been used to infer the global star formation rate density at this epoch (z «6), and we are now beginning to constrain the contribution to reionization of the UV flux from these galaxies. Infrared data from the Spitzer Space Telescope has been used to determine the Spectral Energy Distributions (SEDs) from the rest-frame UV to the optical of some i′-drops, and constrain the previous star formation histories, masses and age of these sources. The indications are that much of the stellar mass of these galaxies might have formed in vigorous bursts at z > 6. The next big advances would be to test the population synthesis modelling of these z ∼ 6 galaxies through spectroscopy of the rest-frame optical (rather than crude broad-band SEDs), and also to push the observational horizon for galaxies further to directly explore star formation during the reionization epoch. JWST is likely to have a profound impact on realising these goals. © Società Italiana di Fisica.

Abstract:

The analysis of Lyman-break galaxies lying at z > 5 has greatly enhanced our understanding of star formation at this cosmologically important epoch. However the vast majority of candidate galaxies at these redshifts either lack spectroscopic confirmation or were selected for their extreme youth and strong Lyman-α emission. Spectroscopy is essential both to constrain the redshifts and properties of the candidate galaxies, and to eliminate lower-redshift interlopers. We discuss results from our recent spectroscopy of high-redshift, rest-UV selected sources using 8 and 10 m telescopes and the contribution of such observations to our overall understanding of the cosmological evolution of the galaxy population. © Società Italiana di Fisica.

Abstract:

We present the results of an optical and near-IR spectroscopic study of giant nebular emission-line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07, and B2 0902+34. Previous deep narrowband Lyα imaging revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s-1 and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions > 1000 km ss-:. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of ≈60 kpc along the radio axis. The dynamical structures traced in the Lyα line are, in most cases, closely echoed in the carbon and oxygen lines. This shows that the Lyα line is produced in a highly clumped medium of small filling factor and can therefore be used as a tracer of the dynamics of high-redshift radio galaxies (HzRGs). We conclude that these HzRGs are under-going a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming "red and dead" elliptical galaxies. © 2007, The American Astronomical Society. All rights reserved.