Professor Andrew Bunker

Abstract:

We describe an observation designed to find H emission from galaxies at z712 made using the InfraRed spectrograph (IRS) on the Spitzer Space Telescope. © 2007 International Astronomical Union.

Abstract:

We discuss the selection of star-forming galaxies at z6 through the Lyman-break technique. Spitzer imaging implies many of these contain older stellar populations (>200Myr) which produce detectable Balmer breaks. The ages and stellar masses (1010M) imply that the star formation rate density at earlier epochs may have been significantly higher than at z6, and might have played a key role in re-ionizing the universe. © 2007 International Astronomical Union.

Abstract:

We exploit the gravitational potential of massive cluster lenses to probe the emission-line properties of six galaxies which appear as highly magnified luminous arcs. Using the Gemini Multi-Object Spectrograph (GMOS) integral field spectrograph together with detailed cluster lens models, we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to ∼0.5 kpc (unlensed) at . Four of the galaxies have stable disc-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I-band Tully-Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B band, the observations suggest of brightening, consistent with increased star-formation activity at . However, the galaxies with stable disc kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counterparts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high-redshift Universe than that possible with conventional surveys. © 2006 RAS.

Abstract:

We have demonstrated the first near-infrared multi-object spectrograph, CIRPASS, on the 4.2-m William Herschel Telescope (WHT) and the 3.9-m Anglo-Australian Telescope. We have conducted an H survey of 38 0.77 < z < 1 galaxies over ∼100 arcmin2 of the Hubble Deep Field North and Flanking Fields, to determine star formation rates (SFRs) using CIRPASS on the WHT. This represents the first successful application of this technique to observing high redshift galaxies (Doherty et al. 2004). Stacking the spectra in the rest-frame, we find a lower limit (uncorrected for dust reddening) on the star formation rate density at redshift z = 1 of 0.04 M yr1 Mpc 3 (Doherty et al. 2006). This implies rapid evolution in the star formation rate density from z = 0 to z = 1 which is proportional to (1 + z) 3.1. We intend to extend our work with FMOS on Subaru as the evolSMURF project (the Evolution of Star-formation and Metallicity in the Universe at high Redshift with FMOS). This will represent nearly two orders-of-magnitude improvement on previous work, and for the first time will provide a sample of sufficient size to measure accurately the H luminosity function, and so determine the global star formation rate using the same indicator as used in local surveys. Using [O II]3727 , H, [O III] 5007 and H redshifted into the z, J & H bands, we can chart the star formation history over 70% of the age of the Universe, affording complete coverage up to z = 1.6 with the same well-understood diagnostics. The line ratios will also allow the extinction and metallicity to be measured at z>1. This will resolve one of the long-standing puzzles in extragalactic astrophysics the true evolution of the Madau-Lilly diagram of star formation density. © 2007 International Astronomical Union.

Abstract:

We determine the abundance of i′-band drop-outs in the HST/ACS GOODS surveys and the Hubble Ultra Deep Field (UDF). The majority of these sources are likely to be z ≈ 6 galaxies whose flux decrement between the F775W i′-band and F850LP z′-band arises from Lyman-α absorption. We have shown with Keck/DEIMOS and Gemini/GMOS spectroscopy that this technique does indeed select high redshift galaxies, and we discovered Lyman-α emission in the expected redshift range for about a third of the galaxies with z′AB < 25.6 in the 150 arcmin2 of the GOODS-South field. The i-drop number counts in the GOODS-North field are consistent, so cosmic variance is possibly not be the dominant uncertainty. The increased depth of UDF enables us to reach a ∼10σ limiting magnitude of z′AB = 28.5 (equivalent to 1.5 h70-2 M⊙ yr-1 at z = 6.1, or 0.1 LUV* for the z ≈ 3 U-drop population). The star formation rate at z ≈ 6 was approximately ×6 less than at z ≈ 3. This declining comoving star formation rate (0.005 h70 M⊙ yr-1 Mpc-3 at z ≈ 6 at LUV > 0.1L* for a Salpeter IMF) poses an interesting challenge for models which suggest that LUV > 0.1L* star forming galaxies at z ≃ 6 reionized the universe. The short-fall in ionizing photons might be alleviated by galaxies fainter than our limit, or a radically different IMF. Alternatively, the bulk of reionization might have occurred at z ≫ 6. We have recently discovered evidence of an early epoch of star formation in some of the i′-drops at z ≈ 6. Spitzer images with IRAC at 3.6-4.5 μm show evidence of the age-sensitive Balmer/4000 Å, dominated by stars older than 100 Myr (and most probably 400 Myr old). This pushes the formation epoch for these galaxies to zform = 7.5-13.5. There are at least some galaxies already assembled with stellar masses ≈3 × 1010 M⊙ (equivalent to 0.2 M* today) within the first billion years. The early formation of such systems may have played a key role in reionizing the Universe at z ∼ 10. © 2005 Elsevier B.V. All rights reserved.