The Astrophysics Department has a strong involvement in the
2dF Galaxy Redshift Survey (2dFGRS). This project, involving
a team of 30 astronomers from Australia and the UK, is the largest
ever redshift survey undertaken, and exploits the unique capabilities
of the Two Degree
Field (2dF) Spectrograph facility on the 3.9m Anglo-Australian
Telescope. This instrument is able to obtain spectra for 400
objects simultaneously over a 2 degree field of view - a capability
which at the moment is unrivalled by any other telescope in
the world!
The goal of 2dFGRS is to secure high quality spectra and
redshifts for 250,000 galaxies brighter than b(J)=19.5 over
2,000 square degrees ofsky. This sky coverage consists of
two long strips, one in the southern galactic cap and the
other in the northern galactic cap equatorial region, plus
100 randomly distributed 2 degree fields within the southern
galactic cap region. These regions have been previously imaged
as part of the APM Survey and it is this survey which provides
the input catalogue for the 2dFGRS. The arrangement of the
2dFGRS survey fields on the sky is shown below:
With 2dFGRS obtaining an order of magnitude more redshifts
than have ever been collected in any previous such survey,
it will be able to address some of the most fundamental problems
in large-scale sturcture, galaxy formation and cosmology.
These are summarised below; areas of investigation being pursued
at UNSW are highlighted:
- Accurate measurement of the power spectrum of galaxy clustering
on scales >30Mpc/h allowing, for the first time, a direct
comparison with microwave background anisotropy measurements
of fluctuations on the same spatial scales.
- Measurements of the distortion of the clustering pattern
in redshift space providing constraints on the cosmological
density parameter, Omega, and the
spatial distribution of dark matter.
- A determination of variations in
the spatial and velocity distributions of galaxies as a
function of luminosity, type and
star-formation history, providing important constraints
on models of galaxy formation.
- Investigations of the morphology of galaxy clustering
and the statistical properties of the fluctuations, e.g.
whether the initial fluctuations are Gaussian as predicted
by inflationary models of the early universe.
- A study of clusters and groups of
galaxies in the redshift survey, in particular the space
density of such systems, their distribution in velocity
dispersion, and the spectral properties of their constituent
members.
- Application of novel techniques to classify the uniform
sample of 250,000 spectra obtained in the survey, thereby
obtaining a comprehensive inventory of galaxy types as a
function of spatial position within the survey.
Survey progress and results
The survey reached the 100,000 redshift mark in May 2000,
and at its current rate of progress should be completed by
the end of 2001. The following plots highlight some of the
results that have been obtained so far, including those to
come from work being conducted here at UNSW:
The redshift cone plot based on the 112,867 galaxies observed
as at the end of July 2000. The extent to which the data are
revealing, in such delicate detail, the full range of large-scale
structure that characterizes the galaxy distribution is clearly
evident. When the survey is complete, it will provide such
3-dimensional maps of the galaxy distribution within a volume
of 100,000,000 cubic Megaparsecs.
Examples of some the known rich Abell clusters that lie within
the 2dFGRS and which are the subject of a detailed study here
at UNSW. Such cone diagrams, which can be constructed from
the survey data, allow us to precisely locate the clusters
along our line of sight, to determine which galaxies are true
members, and thus study bonda fide cluster populations
free of contamination by galaxies and groups that are both
in front and behind the cluster. This approach is being used
to amass highly accurate redshift, velocity dispersion, and
spectral line index information for a large (N=200-300) and
complete sample of clusters and their galaxies, in an effort
to understand stucture/galaxy formation and evolution within
these very dense systems.
Another important area of investigation at UNSW is the search
for `E+A' galaxies within the 2dFGRS and to determine in which
environments they reside. These enigmatic galaxies, which
are characterized by spectra with very strong Balmer absorption
lines and no significant emission, have been commonly found
in the cores of distant rich clusters. The enormous size of
the 2dFGRS sample will allow us to determine whether, at lower
redshifts, such objects are peculiar to the rich cluster environment
or are more widespread. The figure above shows our means of
detecting `E+A' galaxies in an objective way via the analysis
of the equivalent widths of the [OII]3727 emission line and
the mean of the Hß, H-gamma
and H-delta absorption lines. Galaxies
which simultaneously have EW([OII])<5A and EW(Hß+H-gamma+H-delta)>3A
are defined as `E+A' galaxies; the 32 that we have identified
from a sample of 90,000 spectra are clearly seen. We are in
the process of determining what environments they are located.
Press release: Weighing
the Universe with 100,000 galaxies
Fly-through movie: A
trip through the universe!
For more information: The
2dFGRS Home Page
Staff and students involved in 2dFGRS:
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