and Cosmology

8. Cosmology III: The Cosmological Parameters
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surveys is that the FIR flux is nearly unaffected by Galactic
absorption, an effect that needs to be corrected
for when galaxies are selected from optical photometry.
Furthermore, the PSCz is an “all-sky” survey, containing
the galaxy distribution in a sphere around us, so that
we obtain a complete picture of the local galaxy distribution.
However, one needs to be aware of the fact
that in selecting galaxies via their FIR emission one
is thus selecting a particular type of galaxy, predominantly
those which have a high dust content and active
star formation which heats the dust.
The Canada–France Redshift Survey (CFRS) obtained
spectroscopy of faint galaxies with 17.5 ≤ I ≤
22.5, with a median redshift of about 0.5. The resulting
catalog contains 948 objects, 591 of which are galaxies.
This survey was performed by a multi-object spectrograph
at the CFHT (see Sect. 1.3.3) which was able to
take the spectra of up to 100 objects simultaneously.
For the first time, due to its faint limiting magnitude it
enabled us to study the evolution of (optically-selected)
galaxies, for example by means of their luminosity function
and their star-formation rate, and to investigate the
redshift dependence of the galaxy correlation function –
and thus to see the evolution of the large-scale structure.
Currently, two large spectroscopic surveys with faint
limiting magnitudes are being carried out. Both of them
use high multiplex spectrographs mounted on 10-m
class telescopes: the VIMOS instrument on the VLT
and the DEIMOS instrument on Keck. The target of
both surveys, the VIMOS VLT Deep Survey (VVDS)
and the DEEP2 survey, is to obtain spectra of several
tens of thousands of galaxies with z ∼ 1, thus extending
the CFRS by more than an order of magnitude in
sample size and by ∼ 1.5 magnitudes in depth.
The 2dF Survey and the Sloan Digital Sky Survey.
The scientific results from the first redshift surveys motivated
the production of considerably more extended
surveys. By averaging over substantially larger volumes
in the Universe, it was expected that the statistics on the
galaxy distribution could be significantly improved. In
addition, the analysis of the galaxy distribution at higher
redshift would also enable a measurement of the evolution
in the galaxy distribution. Two very extensive redshift
surveys were performed with these main objectives
in mind: the two-degree Field Galaxy Redshift Survey
(2dFGRS) and the Sloan Digital Sky Survey (SDSS).
The 2dFGRS was carried out using a spectrograph
specially designed for this project, which was mounted
at the 4-m Anglo Australian Telescope. Using optical
fibers to transmit the light of the observed objects from
the focal plane to the spectrograph, up to 400 spectra
could be observed simultaneously over a usable field
with a diameter of 2 ◦ . The positioning of the individual
fibers on the location of the pre-selected objects was
performed by a robot. The redshift survey covered two
large connected regions in the sky, of 75 ◦ × 15 ◦ and
75 ◦ × 7.5 ◦ , plus 100 additional, randomly distributed
fields. This survey geometry was chosen so as to yield
the optimal cosmological information about the galaxy
distribution, that is, the most precise measurement of the
correlation function at relevant scales. The photometric
input catalog was the APM galaxy catalog which had
been compiled from digitized photographic plates. The
limiting magnitude of the galaxies for which spectra
were obtained is approximately B 19.5, where this
value is corrected for Galactic extinction. The 2dFGRS
has been completed, and it contains redshifts for more
than 230 000 galaxies (see Fig. 7.1). The spectra and
redshifts are publicly available. The scientific yield from
this large data set is already very impressive, as we will
show further below.
For the SDSS, a dedicated telescope was built,
equipped with two instruments. The first is a camera
with 30 CCDs which has scanned nearly a quarter of
the sky in five photometric bands, generating by far the
largest photometric sky survey with CCDs. The amount
of data collected in this survey is enormous, and its
storage and reduction required a tremendous effort. For
this photometric part of the Sloan Survey, a new photometric
system was developed, with its five filters (u,
g, r, i, z) chosen such that their transmission curves
overlap as little as possible (see Appendix A.4). The
selection of targets for spectroscopy was carried out using
this photometric information. As in the 2dF Survey,
the multi-object spectrograph used optical fibers, and in
this case these had to be manually installed in holes that
had been punched into a metal plate. With about 640 simultaneously
observed spectra, the strategy was similar
to that for the 2dFGRS. The aim of the spectroscopic
survey was to obtain about a million galaxy spectra.
The data products of the SDSS have been made publicly
available at regular intervals, and currently (2006)
about half of the survey has been published. For the