6.1 The latest galaxy
redshift surveys
Redshifts surveys in the 1980s and the 1990s (e.g., the CfA, IRAS,
and Las campanas surveys) measured thousands to tens of thousands
galaxy redshifts. Multifibre technology now allows us to measure
redshifts of millions of galaxies. Below we summarize briefly the
properties of the main new surveys 2dFGRS, SDSS, 6dF, VIRMOS,
DEEP2, and we discuss key results from 2dFGRS and SDSS. Further
analysis of these surveys is currently underway.
6.1.1
The 2dF galaxy
redshift survey
The Anglo-Australian 2-degree Field Galaxy
Redshift (2dFGRS) [89] has recently been
completed with redshifts for 230,000 galaxies selected from the APM
catalogue December 2002) down to an extinction corrected magnitude
limit of
. The main survey regions are two
declination strips, in the northern and southern Galactic
hemispheres, and also 100 random fields, covering in total about
(see Figures 20 and 21). The median redshift
of the 2dFGRS is
(see [11, 65] for
reviews).
6.1.2
The SDSS galaxy
redshift survey
The SDSS (Sloan Digital Sky Survey) is a
U.S.-Japan-Germany joint project to image a quarter of the
Celestial Sphere at high Galactic latitude as well as to obtain
spectra of galaxies and quasars from the imaging data[93]. The dedicated
2.5 meter telescope at Apache Point Observatory is equipped with a
multi-CCD camera with five broad bands centered at
,
,
,
, and
Å. For further details of SDSS, see [102, 80]
The latest map of the SDSS galaxy distribution,
together with a typical slice, are shown in Figures 22 and 23 (see also [32
]). The
three-dimensional map centered on us in the equatorial coordinate
system is shown Figure 22. Redshift slices of
galaxies centered around the equatorial plane with various redshift
limits and thicknesses of planes are shown in Figure 23:
with thickness of
centered
around the equatorial plane in the upper-left panel;
with a thickness of
in the
upper-right panel;
with a thickness of
in the lower panel.
6.1.3
The 6dF galaxy
redshift survey
The 6dF (6-degree Field) [91] is a survey of
redshifts and peculiar velocities of galaxies selected primarily in
the Near Infrared from the new 2MASS (Two Micron All Sky Survey)
catalogue[90]. One goal is
to measure redshifts of more than 170,000 galaxies over nearly the
entire Southern sky. Another exciting aim of the survey is to
measure peculiar velocities (using 2MASS photometry and 6dF
velocity dispersions) of about 15,000 galaxies out to
. The high quality data of this survey could revive
peculiar velocities as a cosmological probe (which was very popular
about 10-15 years ago). Observations have so far obtained nearly
40,000 redshifts and completion is expected in 2005.
6.1.4
The DEEP galaxy
redshift survey
The DEEP survey is a two-phased project using
the Keck telescopes to study the properties and distribution of
high redshift galaxies [92]. Phase 1 used
the LRIS spectrograph to study a sample of
galaxies to a limit of
. Phase 2 of
the DEEP project will use the new DEIMOS spectrograph to obtain
spectra of
faint galaxies with redshifts
. The scientific goals are to study the evolution of
properties of galaxies and the evolution of the clustering of
galaxies compared to samples at low redshift. The survey is
designed to have the fidelity of local redshift surveys such as the
LCRS survey, and to be complementary to ongoing large redshift
surveys such as the SDSS project and the 2dF survey. The
DEIMOS/DEEP or DEEP2 survey will be executed with resolution
R 4000, and we therefore expect to measure linewidths and
rotation curves for a substantial fraction of the target galaxies.
DEEP2 will thus also be complementary to the VLT/VIRMOS project,
which will survey more galaxies in a larger region of the sky, but
with much lower spectral resolution and with fewer objects at high
redshift.
6.1.5
The VIRMOS galaxy
redshift survey
The on-going Franco-Italian VIRMOS project[94] has
delivered the VIMOS spectrograph for the European Southern
Observatory Very Large Telescope (ESO-VLT). VIMOS is a VIsible
imaging Multi-Object Spectrograph with outstanding multiplex
capabilities: With 10 arcsec slits, spectra can be taken of 600
objects simultaneously. In integral field mode, a 6400-fibre
Integral Field Unit (IFU) provides spectroscopy for all objects
covering a
area. VIMOS therefore
provides unsurpassed efficiency for large surveys. The VIRMOS
project consists of: construction of VIMOS, and a Mask
Manufacturing Unit for the ESO-VLT. The VIRMOS-VLT Deep Survey
(VVDS), a comprehensive imaging and redshift survey of the deep
Universe based on more than 150,000 redshifts in four 4
square-degree fields.