Redshift survey

Source: Wikipedia, the free encyclopedia.
Rendering of the 2dFGRS data.
The positions in space of the galaxies identified by the VIPERS survey.

In

survey of a section of the sky to measure the redshift of astronomical objects
: usually galaxies, but sometimes other objects such as galaxy clusters or quasars. Using
large-scale structure of the universe. In conjunction with observations of early structure in the cosmic microwave background, these results can place strong constraints on cosmological parameters such as the average matter density[1][2] and the Hubble constant.[3]

Generally the construction of a redshift survey involves two phases: first the selected area of the sky is imaged with a wide-field telescope, then galaxies brighter than a defined limit are selected from the resulting images as non-pointlike objects; optionally, colour selection may also be used to assist discrimination between stars and galaxies.[4] Secondly, the selected galaxies are observed by spectroscopy, most commonly at visible wavelengths, to measure the wavelengths of prominent spectral lines; comparing observed and laboratory wavelengths then gives the redshift for each galaxy.

The

Great Wall
, a vast conglomeration of galaxies over 500 million light-years wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.

The first systematic redshift survey was the CfA Redshift Survey of around 2,200 galaxies, started in 1977 with the initial data collection completed in 1982. This was later extended to the CfA2 redshift survey of 15,000 galaxies,[5] completed in the early 1990s.

These early redshift surveys were limited in size by taking a spectrum for one galaxy at a time; from the 1990s, the development of fibre-optic spectrographs and multi-slit spectrographs enabled spectra for several hundred galaxies to be observed simultaneously, and much larger redshift surveys became feasible. Notable examples are the

VIMOS-VLT Deep Survey (VVDS)
; these have around 50,000 redshifts each, and are mainly focused on galaxy evolution.

ZFOURGE or the FourStar Galaxy Evolution Survey is a large and deep medium-band imaging survey which aims to establish an observational benchmark of galaxy properties at redshift z > 1. The survey is using near-infrared FOURSTAR instrument on the Magellan Telescopes, surveying in all three HST legacy fields: COSMOS, CDFS, and UDS.[6]

Because of the demands on observing time required to obtain spectroscopic redshifts (i.e., redshifts determined directly from

LSST
) aim to significantly refine the technique.

See also

References

  1. S2CID 1546652
    .
  2. S2CID 53316788
    .
  3. S2CID 55926132
    .
  4. ^ "SkyServer - Algorithms". sdss.org. Retrieved 18 August 2014.
  5. S2CID 14298026
    .
  6. ^ "Zfourge".

External links

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