Heath Jones

The SAMI Galaxy Survey: cubism and covariance, putting round pegs into square holes

We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney–AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ∼3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume.

SAMI: a new multi-object IFS for the Anglo-Australian Telescope

SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our understanding of galaxies, with spatially-resolved spectroscopy of large numbers of targets. It is the first on-sky application of innovative photonic imaging bundles called hexabundles, which will remove the aperture effects that have biased previous single-fibre multi-object astronomical surveys. The hexabundles have lightly-fused circular multi-mode cores with a covering fraction of 73%. The thirteen hexabundles in SAMI, each have 61 fibre cores, and feed into the AAOmega spectrograph at the Anglo-Australian Telescope (AAT). SAMI was installed at the AAT in July 2011 and the first commissioning results prove the effectiveness of hexabundles on sky. A galaxy survey of several thousand galaxies to z 0.1 will begin with SAMI in mid-2012.

TTF survey of galaxy populations

The TAURUS Tunable Filter (TTF) affords a new approach to observational cosmology, allowing a wide field (10 arcmin) to be imaged monochromatically in contiguous wavelength intervals (6 - 60 Angstrom bandpass) over the R and I bands. In a 200 s exposure at the AAT, the TTF can detect H-alpha emission powered by star formation rates as low as 0.1 solar mass per year at z = 0.08 and 1 solar mass per year at z = 0.24 in 2 arcsec seeing (cf. 0.26 solar mass per year for the LMC). In this paper we describe an emission-line survey currently underway using the TTF on the AAT to detect redshifted H-alpha over the ranges z = 0.06 - 0.1 and z = 0.22 - 0.26. Such detections will be of timely interest to the Southern HI Sky Survey which is motivated along similar lines.

Scaling relations of early-type galaxies in the 6dF Galaxy Survey

Over 10,000 early-type galaxies from the 6dF Galaxy Survey (6dFGS) (Jones, D. H. et al . (2009), Jones et al . (2004)) have been used to determine the Fundamental Plane at optical and near-infrared wavelengths. We find that a maximum likelihood fit to an explicit three-dimensional Gaussian model for the distribution of galaxies in size, surface brightness and velocity dispersion can precisely account for selection effects, censoring and observational errors, leading to precise and unbiased parameters for the Fundamental Plane and its intrinsic scatter.

Galaxy And Mass Assembly (GAMA)

The GAMA survey aims to deliver 250,000 optical spectra (3–7 A resolution) over 250 sq. degrees to spectroscopic limits of r AB K AB z ≈ 0.4. Key science drivers include the measurement of: the halo mass function via group velocity dispersions; the stellar, HI, and baryonic mass functions; galaxy component mass-size relations; the recent merger and star-formation rates by mass, types and environment. Detailed modeling of the spectra, broad SEDs, and spatial distributions should provide individual star formation histories, ages, bulge-disc decompositions and stellar bulge, stellar disc, dust disc, neutral HI gas and total dynamical masses for a significant subset of the sample (~ 100k) spanning both the giant and dwarf galaxy populations. The survey commenced March 2008 with 50k spectra obtained in 21 clear nights using the Anglo Australian Observatorys new multi-fibre-fed bench-mounted dual-beam spectroscopic system (AAΩ).

The 6dF Galaxy Survey: a low-redshift benchmark for bulge-dominated galaxies

The 6dF Galaxy Survey provides a very large sample of galaxies with reliable measurements of Lick line indices and velocity dispersions. This sample can be used to explore the correlations between mass and stellar population parameters such as age, metallicity and [α/Fe]. Preliminary results from such an analysis are presented here, and show that age and metallicity are significantly anti-correlated for both passive and star-forming galaxies. Passive galaxies have strong correlations between mass and metallicity and between age and α-element over-abundance, which combine to produce a downsizing relation between age and mass. For old passive galaxies, the different trends of M / L with mass and luminosity in different passbands result from the differential effect of the mass–metallicity relation on the luminosities in each passband. Future work with this sample will examine the Fundamental Plane of bulge-dominated galaxies and the influence of environment on relations between stellar population parameters and mass.