The latest galaxy redshift surveys

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 $bJ < 19.45$ . The main survey regions are two declination strips, in the northern and southern Galactic hemispheres, and also 100 random fields, covering in total about $2 1800 deg$ (see Figures 20 and 21 ). The median redshift of the 2dFGRS is $¯z ∼ 0.1$ (see [11 , 65 ] for reviews).

Figure 20: The 2dFGRS fields (small circles) superimposed on the APM catalogue area (dotted outlines of Sky Survey plates).

Figure 21: The distribution of 63,000 2dFGRS galaxies in the NGP (left panel) and SGP (right panel) strips.

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 3561, 4676, 6176, 7494, and 8873 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 : $z < 0.05$ with thickness of $10h −1 Mpc$ centered around the equatorial plane in the upper-left panel; $z < 0.1$ with a thickness of $−1 15h Mpc$ in the upper-right panel; $z < 0.2$ with a thickness of $−1 20h Mpc$ in the lower panel.

Figure 22: 3D redshift-space map centered on us, and its projection on the celestial sphere of SDSS galaxy subset, including the three main regions. (Figure taken from [32

].)

Figure 23: Redshift slices of SDSS galaxy data around the equatorial plane. The redshift limits and the thickness of the planes are $z < 0.05$ and $10h −1 Mpc$ (upper panel), $z < 0.1$ and $−1 15h Mpc$ (middle panel), and $z < 0.2$ and $−1 20h Mpc$ (lower panel). The size of points has been adjusted. Note that the data for the Southern part are sparser than those for the Northern part, especially for thick slices. (Figure taken from [32

].)

6.1.3 The 6dF galaxy redshift survey

The 6dF (6-degree Field) [90 ] 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[94 ]. 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 $150h −1 Mpc$ . 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 [91 ]. Phase 1 used the LRIS spectrograph to study a sample of $∼$ 1000 galaxies to a limit of I = 24.5. Phase 2 of the DEEP project will use the new DEIMOS spectrograph to obtain spectra of $∼$ 65,000 faint galaxies with redshifts $z ∼ 1$ . 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[92 ] 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 $2 54 × 54 arcsec$ 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.