Professor Andrew Bunker

Abstract:

The study of the physical properties of high-redshift galaxies has become one of the major goals of extragalactic astronomy. In particular the massassembly histories of galaxies have been the focus of many studies at redshifts 1 to 3. In the purpose of probing the dynamics of intermediate and high-redshift galaxies, we have designed a research program to carry out a near-infrared spectroscopic follow up of spatially resolved distant galaxies. Here, we present the results for A370-A5 (z=1.341), an arc behind the lens cluster Abell 370 (z=0.374), observed in the case of science verification programme of SINFONI/VLT. The natural magni fication due to massive galaxy clusters allows to spatially resolve and constrain the dynamics of young star forming galaxies 1 to 3 magnitudes fainter than those selected in blank fields. Thus, the study of lensed galaxies allows to probe a low mass regime of galaxies not accessible in standard observation. In this particular case, we found that the gas distribution and kinematics are consistent with a bipolar outflow with a range of velocities of v ∼ 100km/s. © 2007 Springer-Verlag Berlin Heidelberg.

Abstract:

We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km∈s-1 and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km∈s-1. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of 60 kpc along the radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most of their interstellar medium before evolving to become "red and dead" Elliptical galaxies. © 2007 Springer Science+Business Media B.V.

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.