We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object ...IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.
Mon.Not.Roy.Astron.Soc.370:1213-1222,2006 We have investigated the properties of a volume and magnitude limited sample
of nearby early type galaxies that were carefully selected from the AAO two
...degree field galaxy redshift survey. We used images from the DSS to confirm the
E/S0 morphologies, and augmented this sample with field galaxies from Colbert
et al. 2001. We present spectroscopic observations of 22 galaxies from the
combined sample, from which central velocity dispersions and the Lick stellar
population indices were measured. After carefully correcting the spectra for
nebular emission we derived luminosity-weighted ages, metallicities, and
alpha-element abundance ratios. We compare these isolated galaxies with samples
of early-type galaxies in the Virgo and Coma clusters, and also with the sample
of galaxies in low-density regions of Kuntschner et al. (2002). We find that
galaxies in low-density environments are younger and have a greater spread of
ages compared to cluster galaxies. They also show a wider range of
metallicities at a given velocity dispersion than cluster galaxies, which
display only super-solar metallicities. On average cluster, as well as,
isolated galaxies show non-solar abundance ratios in alpha-elements, suggesting
that, independent of galactic environment, star formation occurred on short
time-scales. We reason that early-type galaxies in low-density environments
experienced merging-induced star-formation episodes over a longer and more
recent period of time compared to a cluster environment, and speculate that a
considerable fraction of their stars formed out of low-metallicity halo gaseous
material during the slow growth of a stellar disk between merging events.
The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematics from ...non-linear structure formation, redshift-space distortions and galaxy bias than previous surveys. We obtain a upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.
Astrophys.J.458:435,1996 We examine the structure and dynamics of the galaxies in the Coma cluster
using a catalog of 552 redshifts including 243 new measurements. The velocity
distribution is shown ...to be non-Gaussian due to structure associated with the
group of galaxies around NGC4839, 40 arcmin SW of the cluster core. We apply a
mixture-modelling algorithm to the galaxy sample and obtain a robust partition
into two subclusters which we use to examine the system's dynamics. We find
that the late-type galaxies are freely-falling into a largely virialised
cluster core dominated by early types. We obtain a virial mass for the main
cluster in close agreement with the estimates derived from recent X-ray data.
The mass of the NGC4839 group is about 5-10% the mass of the main cluster.
Assuming the main cluster and the NGC4839 group follow a linear two-body orbit,
the favored solution has the two clusters lying at 74 degrees to the line of
sight at a true separation of 0.8 Mpc and moving together at 1700 km/s. The
cluster core shows evidence of an ongoing merger between two subclusters
centered in projection on the dominant galaxies NGC4874 and NGC4889 but offset
in velocity by 300 km/s and 1100 km/s respectively. Combining these results
with X-ray and radio observations, and an interpretation of the presence or
lack of an extended halo around the dominant galaxies, we develop a merger
history for the Coma cluster.
This paper describes the first catalogue of photometrically-derived stellar
mass estimates for intermediate-redshift (z < 0.65) galaxies in the Galaxy And
Mass Assembly (GAMA) spectroscopic redshift ...survey. These masses, as well as
the full set of ancillary stellar population parameters, will be made public as
part of GAMA data release 2. Although the GAMA database does include NIR
photometry, we show that the quality of our stellar population synthesis fits
is significantly poorer when these NIR data are included. Further, for a large
fraction of galaxies, the stellar population parameters inferred from the
optical-plus-NIR photometry are formally inconsistent with those inferred from
the optical data alone. This may indicate problems in our stellar population
library, or NIR data issues, or both; these issues will be addressed for future
versions of the catalogue. For now, we have chosen to base our stellar mass
estimates on optical photometry only. In light of our decision to ignore the
available NIR data, we examine how well stellar mass can be constrained based
on optical data alone. We use generic properties of stellar population
synthesis models to demonstrate that restframe colour alone is in principle a
very good estimator of stellar mass-to-light ratio, M*/Li. Further, we use the
observed relation between restframe (g-i) and M*/Li for real GAMA galaxies to
argue that, modulo uncertainties in the stellar evolution models themselves,
(g-i) colour can in practice be used to estimate M*/Li to an accuracy of < ~0.1
dex. This 'empirically calibrated' (g-i)-M*/Li relation offers a simple and
transparent means for estimating galaxies' stellar masses based on minimal
data, and so provides a solid basis for other surveys to compare their results
to z < ~0.4 measurements from GAMA.
We report the morphological classification of 3727 galaxies from the Galaxy and Mass Assembly survey with M_r < -17.4 mag and in the redshift range 0.025 < z < 0.06 (2.1 x 10^5 Mpc^3 ) into E, S0-Sa, ...SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr and little blue spheroid classes. Approximately 70% of galaxies in our sample are disk dominated systems, with the remaining ~30% spheroid dominated. We establish the robustness of our classifications, and use them to derive morphological-type luminosity functions and luminosity densities in the ugrizYJHK passbands, improving on prior studies that split by global colour or light profile shape alone. We find that the total galaxy luminosity function is best described by a double-Schechter function while the constituent morphological-type luminosity functions are well described by a single-Schechter function. These data are also used to derive the star-formation rate densities for each Hubble class, and the attenuated and unattenuated (corrected for dust) cosmic spectral energy distributions, i.e., the instantaneous energy production budget. While the observed optical/near-IR energy budget is dominated 58:42 by galaxies with a significant spheroidal component, the actual energy production rate is reversed, i.e., the combined disk dominated populations generate ~1.3x as much energy as the spheroid dominated populations. On the grandest scale, this implies that chemical evolution in the local Universe is currently confined to mid-type spiral classes like our Milky Way.
We examine the structure and dynamics of the galaxies in the Coma cluster using a catalog of 552 redshifts including 243 new measurements. The velocity distribution is shown to be non-Gaussian due to ...structure associated with the group of galaxies around NGC4839, 40 arcmin SW of the cluster core. We apply a mixture-modelling algorithm to the galaxy sample and obtain a robust partition into two subclusters which we use to examine the system's dynamics. We find that the late-type galaxies are freely-falling into a largely virialised cluster core dominated by early types. We obtain a virial mass for the main cluster in close agreement with the estimates derived from recent X-ray data. The mass of the NGC4839 group is about 5-10% the mass of the main cluster. Assuming the main cluster and the NGC4839 group follow a linear two-body orbit, the favored solution has the two clusters lying at 74 degrees to the line of sight at a true separation of 0.8 Mpc and moving together at 1700 km/s. The cluster core shows evidence of an ongoing merger between two subclusters centered in projection on the dominant galaxies NGC4874 and NGC4889 but offset in velocity by 300 km/s and 1100 km/s respectively. Combining these results with X-ray and radio observations, and an interpretation of the presence or lack of an extended halo around the dominant galaxies, we develop a merger history for the Coma cluster.
The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies in the distant universe, measured with the AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope (AAT). The target ...galaxies are selected using ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8 mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The primary aim of the survey is to precisely measure the scale of baryon acoustic oscillations (BAO) imprinted on the spatial distribution of these galaxies at look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will measure the BAO scale to better than 2% and the tangential and radial acoustic wave scales to approximately 3% and 5%, respectively. This paper provides a detailed description of the survey and its design, as well as the spectroscopic observations, data reduction, and redshift measurement techniques employed. It also presents an analysis of the properties of the target galaxies, including emission line diagnostics which show that they are mostly extreme starburst galaxies, and Hubble Space Telescope images, which show they contain a high fraction of interacting or distorted systems. In conjunction with this paper, we make a public data release of data for the first 100,000 galaxies measured for the project.
Abstract
We use more than 110 500 galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the b
J-band galaxy luminosity function at redshift z= 0, taking account of evolution, the ...distribution of magnitude measurement errors and small corrections for incompleteness in the galaxy catalogue. Throughout the interval −16.5 > − 5 log10
h > −22, the luminosity function is accurately described by a Schechter function with − 5 log10
h=−19.66 ± 0.07, α=−1.21 ± 0.03 and Φ★= (1.61 ± 0.08) × 10−2
h
3 Mpc−3, giving an integrated luminosity density of ρ
L
= (1.82 ± 0.17) × 108
h L⊙ Mpc−3 (assuming an Ω0= 0.3, Λ0= 0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zero-point, from large-scale structure in the galaxy distribution and, importantly, from the uncertainty in the appropriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than, an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the b
J band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on apparent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented.
We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey and the 2dF-SDSS LRG and QSO (2SLAQ) survey carefully ...matched to have the same rest-frame colours and luminosity. We study the spatial two-point auto-correlation function in both redshift-space and real-space of a combined sample of over 10,000 LRGs, which represent the most massive galaxies in the universe with stellar masses > 10^11 h^-1 M_sun and space densities 10^-4 h^-3 Mpc^-3. We find no significant evolution in the amplitude r_0 of the correlation function with redshift, but do see a slight decrease in the slope with increasing redshift over 0.19 < z < 0.55 and scales of 0.32 < r < 32 h^-1 Mpc. We compare our measurements with the predicted evolution of dark matter clustering and use the halo model to interpret our results. We find that our clustering measurements are inconsistent (>99.9% significance) with a passive model whereby the LRGs do not merge with one another; a model with a merger rate of 7.5 +/- 2.3% from z = 0.55 to z = 0.19 (i.e. an average rate of 2.4% Gyr^-1) provides a better fit to our observations. Our clustering and number density measurements are consistent with the hypothesis that the merged LRGs were originally central galaxies in different haloes which, following the merger of these haloes, merged to create a single Brightest Cluster Galaxy. In addition, we show that the small-scale clustering signal constrains the scatter in halo merger histories. When combined with measurements of the luminosity function, our results suggest that this scatter is sub-Poisson. While this is a generic prediction of hierarchical models, it has not been tested before.
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