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multifibre technology now allows us to measure redshifts of millions of galaxies . the anglo - australian 2 degree field galaxy redshift survey ( 2dfgrs ) measured redshifts for 230,000 galaxies selected from the apm catalogue .
the survey is now complete and publically available .
the median redshift of the 2dfgrs is @xmath1 , down to an extinction corrected magnitude limit of @xmath2 ( colless et al .
a sample of this size allows large - scale structure statistics to be measured with very small random errors . in this review
we summarize some recent results from the 2dfgrs on clustering and galaxy biasing .
comprehensive recent reviews are given by colless ( 2003 ) and peacock ( 2003 ) .
an initial estimate of the convolved , redshift - space power spectrum of the 2dfgrs has been determined ( percival et al . 2001 ) for a sample of 160,000 redshifts . on scales
@xmath3 , the data are robust and the shape of the power spectrum is not affected by redshift - space or non - linear effects , though the amplitude is increased by redshift - space distortions .
percival et al .
( 2001 ) , efstathiou et al .
( 2002 ) and lahav et al .
( 2002 ) compared the 2dfgrs and cmb power spectra , and concluded that they are consistent with each other .
a key assumption in deriving cosmological parameters from redshift surveys is that the biasing parameter , defined as the ratio of of galaxy to matter power spectra , is constant , i.e. scale independent . on scales of @xmath4
the fluctuations are close to the linear regime , and there are theoretical reasons ( e.g. fry 1996 ; benson et al .
2000 ) to expect that on large scales the biasing parameter should tend to a constant and close to unity at the present epoch .
this is supported by the derived biasing close to unity by combining 2dfgrs with the cmb ( lahav et al .
2002 ) and by the study of the bi - spectrum of the 2dfgrs alone ( verde et al .
2002 ) .
the 2dfgrs power spectrum ( figure 1 ) was fitted in percival et al .
( 2001 ) over the above range in @xmath5 , assuming scale - invariant primordial fluctuations and a @xmath6-cdm cosmology , for four free parameters : @xmath7 , @xmath8 , @xmath9 and the redshift space @xmath10 .
the amplitudes of the linear - theory rms fluctuations are traditionally labeled @xmath11 in mass @xmath12 in galaxies , defined on @xmath13 spheres . assuming a gaussian prior on the hubble constant @xmath14 ( based on freedman et al .
2001 ) the shape of the recovered spectrum within the above @xmath5-range was used to yield 68 per cent confidence limits on the shape parameter @xmath15 , and the baryon fraction @xmath16 , in accordance with the popular ` concordance ' model ( e.g. bahcall et al . 1999 ) . for
fixed ` concordance model ' parameters @xmath17 , @xmath18 and a hubble constant @xmath19 , the amplitude of 2dfgrs galaxies in redshift space is @xmath20 ( at the survey s effective luminosity and redshift ) .
recently the sdss team presented their results for the power spectrum ( tegmark et al .
2003a , b ; pope et al . 2004 ) , and they found good agreement with the 2dfgrs gross shape of the power spectrum .
pope et al .
( 2004 ) emphasize that sdss alone can not break the degeneracy between @xmath7 and @xmath8 because the baryon oscillations are not resolved given window function of the survey .
solar , atmospheric , and reactor neutrino experiments have confirmed neutrino oscillations , implying that neutrinos have non - zero mass , but without pinning down their absolute masses .
while it is established that the effect of neutrinos on the evolution of cosmic structure is small , the upper limits derived from large - scale structure could help significantly to constrain the absolute scale of the neutrino masses .
elgary et al .
( 2002 ) used the 2dfgrs power spectrum ( figure 1 ) to provide an upper limit @xmath21 , i.e. approximately 0.7 ev for each of the three neutrino flavours , or phrased in terms of their contribution to the matter density , @xmath22 .
the wmap team ( spergel et al . 2003 ) reported an improved limit of @xmath23 ( 95% cl ) .
however , we point out that neutrinos with ev masses are basically indistinguishable from cold dark matter at the epoch of last scattering , and therefore they have little effect on the cmb fluctuations .
the main neutrino signature comes from the 2dfgrs and the lyman @xmath24 forest which were combined with the wmap data .
the contribution of wmap is that it constrains better the other parameters involved , e.g. @xmath25 ( see also hannestad 2003 and tegmark et al .
2003b for similar results from sdss+wmap ) . despite the uncertainties involved ,
it is remarkable that the results from redshift surveys give upper limits which are lower than those deduced from laboratory experiments , e.g. tritium decay .
as the suppression of the power spectrum depends on the ratio @xmath26 , elgary & lahav ( 2003 ) found that the out - of - fashion mixed dark matter ( mdm ) model , with @xmath27 , @xmath28 and no cosmological constant , fits the 2dfgrs power spectrum well , but only for a hubble constant @xmath29 .
blanchard et al . ( 2003 ) reached a similar conclusion , and they also found that the cmb power spectrum could be fit well by the same mdm model if one allows features in the primordial power spectrum .
it is intriguing ( and perhaps disappointing ) that the cmb and redshift surveys can not on their own ( i.e. without a strong prior on the hubble constant ) ` prove ' the existence a non - zero cosmological constant .
another consequence of this is that excluding low values of the hubble constant , e.g. with the hst key project , is important in order to get a strong upper limit on the neutrino masses .
madgwick et al . ( 2002 ) have utilized the method of principal component analysis ( pca ) to compress each galaxy spectrum into one quantity , @xmath30 .
it turns out that @xmath31 is a useful indicator of the star formation rate in a galaxy ( madgwick et al .
this allows us to divide the 2dfgrs into @xmath31-types , and to study e.g. luminosity functions and clustering per type .
figures 2 and 3 show the bimodality in this spectral parameter and in the colour distribution ( peacock 2003 ) , respectively .
bimodality is also seen clearly in the sdss photometric and spectroscopic galaxy data ( blanton et al . 2003 , kauffmann et al . 2004 ) .
while the concept of two major galaxy populations in the universe was recognized long time ago by hubble and others , 2dfgrs and sdss provide quantitative measures of the frequency distribution using objective physical measures like spectral features and colours .
the details of these distribution functions pose challenges to models of galaxy formation , in particular regarding the role of feedback mechanisms and the ` nature ' versus ` nurture ' question .
although galaxy biasing was commonly neglected until the early 1980s , it has become evident that on scales @xmath32 different galaxy populations exhibit different clustering amplitudes , the so - called morphology - density relation ( e.g. dresser 1980 ; hermit et al .
biasing on small scales is also predicted in the simulations of hierarchical clustering from cdm initial conditions ( e.g. benson et al .
it is important therefore to pay attention to the scale on which biasing operates .
norberg et al .
( 2002 ) found that for @xmath33 galaxies , the real space correlation function amplitude of @xmath31 early - type galaxies is @xmath34 higher than that of late - type galaxies .
peacock et al . ( 2001 ) , hawkins et al .
( 2003 ) and madgwick et al .
( 2003b ) analysed the redshift space correlation function @xmath35 in terms of the line - of - sight and perpendicular to the line - of - sight separation for the entire galaxy populations , we well as for the most passively ( ` red ' ) and actively ( ` blue ' ) star - forming galaxies separately .
the clustering properties of the two samples are quite distinct on scales @xmath36 .
the ` red ' galaxies display a prominent ` finger - of - god ' effect and also have a higher overall normalization than the ` blue ' galaxies .
figure 4 shows the real space correlation functions for the red and blue galaxies . while both are power laws , the slope is different , in accord with results for populations divided by colour in the sdss ( zehavi et al .
understanding the difference in slope is another challenge for galaxy formation models .
biasing could be non - linear and ` stochastic ' , in the sense that the number of galaxies predicted in a volume is not only a function of the mass fluctuation in that cell , but is possibly affected by other ` hidden variables ' ( dekel & lahav 1999 ) .
wild et al . (
2004 ) found recently evidence for a small amount stochasticity when considered a joint counts in cells of two galaxy populations defined by either colour or spectral type .
the small amount of observed stochasticity supports the use of redshift surveys for measuring matter density fluctuations on large scales .
however , the comparison with theory calls for better understanding of the ` hidden variables ' in models of galaxy formation ( e.g. blanton et al . 2000 ; somerville et al .
the results presented above illustrate the power of redshift surveys to address fundamental issues in galaxy formation and cosmology .
these are only a few examples of the results from the 2dfgrs .
other results and papers are listed on the 2dfgrs website .
overall , the results from 2dfgrs fit well into the ` concordance ' model which has emerged from various cosmological data sets . the @xmath6-cdm model with comparable amounts of dark matter and dark energy is rather esoteric , but it is remarkable that different measurements converge to the ` concordance model ' with parameters .
perhaps the least accurate estimates on that list are for @xmath25 and @xmath11 ( e.g. bridle et al .
2003 , lahav & liddle 2003 ) .
it is intriguing that an einstein - de sitter mixed dark matter model ( cold+hot dark matter ) without a cosmological constant can also fit the data , but it requires a low hubble constant and admittedly is at odds with the sn ia , cluster baryon fraction and other cosmic measurements .
it is however an illustration that other yet unknown models may fit the data equally well
.    it may well be that in the future the cosmological parameters will be fixed by the cmb , sn ia etc .
then , for fixed cosmological parameters , one can use redshift surveys primarily to study galaxy biasing and evolution with cosmic epoch .
i d like to thank joss bland - hawthorn and the ` tully 60 ' conference organisers for the hospitality in sydney .
many of us are grateful to brent tully for his numerous original and inspiring contributions to the exploration of the local universe .
i thank sarah bridle , ystein elgary , pirin erdogdu , darren madgwick , vivienne wild and members of the 2dfgrs and leverhulme quantitative cosmology teams for their contribution to the work summarized here .
the 2df galaxy redshift survey was made possible through the dedicated efforts of the staff of the anglo - australian observatory .
i also acknowledge a pparc senior research fellowship .
peacock j.a . , 2003 , to appear in the proceedings of the 13th annual october astrophysics conference in maryland , ` the emergence of cosmic structure ' , eds .
s. holt and c. reynolds ( aip ) , astro - ph/0301042
the 2df galaxy redshift survey ( 2dfgrs ) of 230,000 redshifts of nearby ( @xmath0 ) galaxies is now complete . 
 it has allowed the 2dfgrs team and others to estimate fundamental cosmological parameters and to study galaxy intrinsic properties . here 
 we highlight three recent key results from the survey : ( i ) an upper limit of about 2ev on the total mass of the three neutrino flavours , and an intriguing reasonable fitting of the 2dfgrs power spectrum to a mixed dark matter model without a cosmological constant , but with a low hubble constant ; ( ii ) the bimodality of the galaxy population in both spectral parameterisation and in colour ; and ( iii ) the clustering of different galaxy types and evidence for relative stochastic biasing .    
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