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since the turn of the millennium , we have witnessed a dramatic improvement in the resolution and accuracy of measurements of fluctuations in the temperature of the cosmic microwave background radiation ( cmb ) . the discovery of features in the power spectrum of the cmb temperature , the acoustic peaks , marked the start of a new , data - rich era in cosmology ( de bernardis et  al . 2000 ; hanany et  al . the relative positions and heights of the acoustic peaks encode information about the values of the fundamental cosmological parameters , such as the curvature of the universe or the physical density in cold dark matter and baryons . perhaps the most striking example of the progress achieved is the first year data from the wmap satellite ( bennett et  al . 2003 ; hinshaw et  al . 2003 ) .    the cmb data alone , however , do not constrain all of the fundamental cosmological parameters to high precision . degeneracies exist between certain combinations of parameters which lead to indistinguishable temperature fluctuation spectra ( efstathiou & bond 1999 ) . some of these degeneracies can be broken by comparing theoretical models to a combination of the cmb data and other datasets , such as the power spectrum of galaxy clustering . at the same time as the new measurements of the cmb were obtained , two groundbreaking surveys of galaxies in the local universe were being conducted . the two - degree field galaxy redshift survey ( 2dfgrs ; colless et  al . 2001 ; 2003 ) and the sloan digital sky survey ( sdss ; york et  al . 2000 ; abazajian et  al . 2005 ) are substantially larger than previous redshift surveys and allow the clustering of galaxies to be measured accurately on all scales . on large scales , the connection to theoretical models is most straightforward . percival et  al . ( 2001 ) used the power spectrum of galaxy clustering measured from the 2dfgrs to constrain the ratio of the baryon to matter density , @xmath11 , and the matter density , @xmath12 . efstathiou et  al . ( 2002 ) used a compilation of pre - wmap cmb data and the percival et  al . measurement of the galaxy power spectrum to find conclusive evidence for a non - zero cosmological constant , independent of the hubble diagram of distant type 1a supernovae . percival et  al . ( 2002 ) again used pre - wmap cmb data and the early 2dfgrs power spectrum measurement to place constraints on cosmological parameters in flat models . the wmap team also used the percival et  al . galaxy power spectrum in their estimation of cosmological parameters ( spergel et  al . other papers have also analyzed the information encoded in the 2dfgrs and sdss power spectra ( tegmark , zaldarriaga & hamilton 2001 ; pope et  al . 2004 ; tegmark et  al . 2004b ; seljak et  al . 2005 ) . in view of the impact of this work , the recent completion by cole et  al . ( 2005 ) of the power - spectrum analysis of the final 2dfgrs dataset is an important development . the cole et  al . results are nearly twice as accurate as those obtained from the part - complete 2dfgrs in 2001 , and a key aim of the current paper is to see how this affects the outcome of joint analyses including cmb data .    in view of these rapid improvements in our knowledge of the cosmological parameters , it is also important to take stock of precisely which parts of the model are actually being tested . quite often , restrictive assumptions have been adopted for the background cosmology when claims are made about the constraints on a particular parameter . it is important to establish how robust the constraints really are when the data are compared with more general cosmological models . our goal is thus to establish firmly how well the latest cmb and large - scale structure ( lss ) data determine a broad set of cosmological parameters , paying attention to how the choice of priors for parameter values and the combination of different parameters can influence the results . the outline of the paper is as follows . in section 2 , we describe the data used in our parameter estimation and set out the various parameter spaces studied . in section 3 , we present our main results for the parameter constraints obtained by comparing theoretical models to the cmb data and the galaxy power spectrum of the final 2dfgrs measured by cole et  al . we assess the impact of different choices for priors and parameter sets in section 4 . we explore the justification for using models with different numbers of free parameters in section 5 . in section 6 , we examine how the parameter constraints change when the sdss galaxy power spectrum measured by tegmark et  al . ( 2004b ) is used instead of the 2dfgrs power spectrum . finally , we summarize our conclusions in section 7 . we now set out the approach we will take to constrain the values of the basic cosmological parameters . in section  [ ssec : data ] , we list the cmb and lss datasets that we compare against the theoretical models and explain how these datasets are modelled . the parameter sets that we will consider are defined in section  [ ssec : param ] . the methodology for searching parameter space and placing constraints on parameters is set out in section  [ ssec : mechanics ] .      in order to constrain the parameters in our cosmological model , we use a compilation of recent measurements of the cmb and the power spectrum of galaxy clustering in the local universe :    * the wmap first year temperature power spectrum for spherical harmonics @xmath13 ( hinshaw et  al . * observations of the temperature spectrum over the spherical harmonic range @xmath14 made up to july 2002 using the arcminute cosmology bolometer array receiver ( acbar ; kuo et  al . * the temperature spectrum for @xmath15 measured using the very small array ( vsa ; dickinson et  al . * two years of temperature correlation data with @xmath16 from the cosmic background imager ( cbi ; readhead et  al . * the wmap first year temperature - polarization power spectrum for spherical harmonics @xmath17 ( kogut et  al . * the power spectrum of galaxy clustering measured from the final 2dfgrs catalogue ( cole et  al . 2005 ) . the four measurements ( i - iv ) of the power spectrum of temperature fluctuations in the cmb extend over the spherical harmonic range @xmath18 . some of the available datasets extend to higher multipoles . however , we do not include these scales in our analysis , as the temperature fluctuations on such scales can be strongly affected by secondary sources . the wmap team adopted a similar approach , augmenting the first year wmap data with other experiments which have better angular resolution ( spergel et  al . however , the vsa data were not available to the wmap team at the time that the paper by spergel et  al . was written . theoretical temperature - temperature and temperature - polarization spectra are computed for each model using camb ( lewis , challinor & lasenby 2000 ) . cole et  al . ( 2005 ) measured the power spectrum of galaxy clustering from the final 2dfgrs catalogue . the power spectrum measured for galaxies differs in a number of ways from the power spectrum for the mass predicted in linear perturbation theory : ( i ) nonlinear evolution of density perturbations leads to coupling between fourier modes , changing the shape of the power spectrum . ( ii ) the galaxy power spectrum is distorted by the gravitationally induced peculiar motions of galaxies when a redshift is used to infer the distance to each galaxy . ( iii ) the power spectrum of the galaxies could be a modified version of the power spectrum of the mass . this phenomenon is known as galaxy bias . the ratio between the galaxy and matter spectra could also change with scale . ( however , we assume a constant bias over the scales considered in this paper ) . ( iv ) the power spectrum measured by cole et  al . from the 2dfgrs is the direct transform of the data , and is thus what cmb researchers would term a pseudo - spectrum . as such , it yields a convolution of the underlying galaxy power spectrum with the modulus squared of the fourier transform of the window function of the survey .    in order to constrain cosmological parameters , these effects need to be modelled . the accuracy of the modelling requires that the comparison between theory and observation should be restricted to a limited range of scales . we use the 2dfgrs power spectrum data for @xmath19 and discard measurements with @xmath20 which could be affected by uncertainties in the mean density of galaxies within the survey . we follow the scheme used by cole et  al . who applied a correction for non - linearity and scale - dependent bias to the shape of @xmath21 of the form @xmath22 where @xmath23 and @xmath24 are the preferred values and b is a constant bias factor . this formula is deduced by comparison with detailed numerical galaxy - formation models : these show that the value of @xmath25 is robust , but the exact value of @xmath26 depends on galaxy type and also has some uncertainty depending on how the modelling is done . these results were used to determine a range of allowed values for @xmath26 , from which the value @xmath24 is preferred ; with this choice , robust parameter constraints are obtained if one considers maximum @xmath27 values beyond our limit of @xmath28 . for this limit , neglecting the correction entirely and simply fitting linear theory yields almost identical results to those presented here . in particular , it has no impact on the marginal indication of a deviation from @xmath6 .      in this paper , we make the basic assumption that the primordial density fluctuations were adiabatic , gaussian and had a power law spectrum of fourier amplitudes . as pointed out by leach & liddle ( 2003a ) , the cmb data prior to wmap were of insufficient quality to justify the rejection of this simple hypothesis . following the release of the wmap first year results , which do have the precision required to test this model , our assumptions remain well motivated . komatsu et al . ( 2003 ) found that the wmap sky maps are consistent with gaussian primordial fluctuations to a much higher precision than was attainable with cobe . peiris et al . ( 2003 ) found that models with a spectral index varying slowly with wavenumber give slightly better fits to the wmap data , particularly when combined with estimates of the power spectrum of the lyman-@xmath29 forest . however , the evidence for a running spectral index is weak and has been disputed by other groups ( e.g. bridle et  al . 2003b ; slosar , seljak & makarov 2003 ; seljak et  al . bennett et  al . ( 2003 ) and spergel et  al . ( 2003 ) point out that , on large scales , a few modes of the cmb temperature power spectrum measured by wmap lie below the predictions of the standard @xmath30cdm model . one interpretation of this apparent discrepancy is that new physics may be needed ( e.g. bridle et  al . 2003a ; efstathiou 2003 ) . however , several studies have argued that the disagreement is actually less significant than was first claimed ( gaztaaga et  al . 2003 ; de oliveira - costa et  al . 2003 ; efstathiou 2004 ) . > from the above starting point , the cosmological model we consider is defined by eleven parameters : @xmath31 there are eight further basic quantities whose values can be derived given the above set : @xmath32 we now go through the parameters in these lists , defining each one and explaining how the values of the derived parameters are obtained . the are five quantities that describe the homogeneous background cosmology through various contributions to the mass - energy density . these are , in units of the critical density : @xmath33 , which describes the curvature of the universe ; @xmath34 , the energy - density of the dark energy ; @xmath35 , the density of the dark matter ( where @xmath36 is the sum of the cold and hot dark matter components and @xmath37 is hubble s constant in units of @xmath38 ) ; @xmath39 , the baryon density ; and @xmath40 the fraction of the dark matter in the form of massive neutrinos . the sum of neutrino masses is given by @xmath41 . the matter density parameter is given by @xmath42 . the value of the hubble constant is derived from @xmath43 . the energy density of the dark energy is set by @xmath44 . the dark energy component is assumed to have an equation of state that is independent of redshift , with the ratio of pressure to density given by @xmath45 . there are four quantities that describe the form of the initial fluctuations ; the spectral indices , @xmath5 and @xmath46 , and the primordial amplitudes , @xmath47 and @xmath48 , of scalar and tensor fluctuations respectively . these parameter values are quoted at the ` pivot ' scale wavenumber of @xmath49 . we can translate the results obtained for @xmath47 into a constraint on the more familiar parameter @xmath50 , the _ rms _ linear perturbation theory variance in spheres of radius @xmath51mpc , using the matter fluctuation transfer function . note that when we consider tensor modes , we make the slow - roll assumption that @xmath52 . the bias factor , @xmath53 , describes the difference in amplitude between the galaxy power spectrum and that of the underlying dark matter . the value of @xmath54 is marginalized over , using the analytic expression given in appendix f of lewis & bridle ( 2002 ) . we assume that the reionization of the neutral intergalactic medium occurred instantaneously , with an optical depth given by @xmath55 ; the redshift of reionization , @xmath56 , depends upon a combination of parameters ( see table 1 of tegmark et  al . the age of the universe is @xmath57 . finally , @xmath58 gives the ratio of the sound horizon scale at the epoch of decoupling to the angular diameter distance to the corresponding redshift and replaces the hubble constant as a base parameter ( kosowsky , milosavljevic & jimenez 2002 ) . we have chosen to use this parameter , rather than , for example , the energy density in dark energy , since it has a posterior distribution that is close to gaussian . this reduces degeneracies between parameters and results in a faster convergence of our search of parameter space ( see section  [ ssec : mechanics ] ) , compared with studies in which parameters such as @xmath34 , which does not have a gaussian posterior distribution , are allowed to vary . this approach is a standard practice even though , usually , the final results are expressed in terms of more familiar parameters such as @xmath34 or @xmath37 . however , care must be taken when comparing our results with those from studies which have assumed flat priors on different parameters in their bayesian analysis . such choices may affect the final results in a way that is difficult to quantify . we do not attempt to vary all eleven parameters of the model at once . such an approach would lead to a mixture of poor estimates of the values of individual parameters and constraints on various combinations of parameters . as we are primarily interested in deriving the best possible constraints on individual parameters , we instead consider subsets of parameter space , varying five , six or seven parameters at a time . of the remaining parameters , some are held at fixed values and the others are referred to as derived parameters . the values of the derived parameters follow from the values of other parameters , once the assumptions made in each parameter space have been taken into account . we will now set out each of our parameter spaces in turn , stating which parameters are varied and which are held fixed . in all cases , the bias parameter , @xmath54 , is marginalized over , so we do not include this in the list of parameters whose values are constrained .    in the simplest case , we vary five parameters which we refer to as the ` basic - five ' ( b5 ) parameter set . the following parameters are allowed to float : @xmath59 the values of the fixed parameters in the basic - five model are : @xmath60 the results of this model are discussed in section 3.2 . the basic - five set is expanded to allow the value of the scalar spectral index to float , giving the basic - six ( b6 ) model ( see section  3.3 ) : @xmath61 the fixed parameters in the basic - six model are : @xmath62    . the parameter space probed in our analysis . we assume a flat prior in each case . we do not vary the values of all parameters at the same time ; the parameter spaces that we consider are set out in section  [ ssec : param ] . [ cols="^,^",options="header " , ]     in this section , we replace the 2dfgrs @xmath21 measured by cole et  al . ( 2005 ) with the power spectrum of sdss galaxies estimated by tegmark et  al . ( 2004a ) and examine the impact that this change has upon the values of the recovered cosmological parameters . there are a number of differences between the two measurements of the galaxy power spectrum . firstly , the sdss is a red - selected survey , while the 2dfgrs is blue - selected . secondly , tegmark et  al . used a sophisticated eigenmode deconvolution apparatus to attempt to remove the effects of the survey window and redshift - space distortions ; in contrast , cole et  al . used a simpler fourier approach that compares to window - convolved models and quantifies redshift - space effects directly by comparison with realistic simulations . tegmark et  al . ( 2004b ) used the wmap first year data and the sdss galaxy power spectrum to constrain cosmological parameters . these authors modelled the galaxy power spectrum with a non - linear model for the matter fluctuations multiplied by a scale independent bias factor . the power spectrum data were used on scales larger than @xmath63 . it is not clear that a constant bias is a good approximation on scales for which the density fluctuations have become non - linear . we adopt a simpler approach and assume that the galaxy power spectrum can be related to the linear perturbation theory power spectrum of the mass through a constant shift in amplitude . as discussed earlier , the simulations used by cole et  al . indicate that redshift - space effects and other nonlinearities are unimportant for the 2dfgrs to our imposed limit of @xmath64 . we repeat the study of parameter space previously carried out using the cmb data plus the 2dfgrs @xmath21 and present our results using the sdss @xmath21 instead in table  5 . for the most part , the results obtained with the sdss @xmath21 are compatible with those found using the 2dfgrs @xmath21 . there are , however , some cases in which the results are quite different . this point is illustrated using the results of the basic - six model in fig . [ fig : b6_sdss ] . in this plot , we compare the parameter constraints obtained using cmb data alone ( dashed line ) with the results for cmb data plus the 2dfgrs @xmath21 ( solid line ) and for cmb data plus the sdss @xmath21 ( dot - dashed line ) . for three out of the six parameters presented , @xmath65 , @xmath55 and @xmath5 , there is impressive agreement between the sets of results ; the peaks in the likelihood distributions coincide in the cmb only and cmb plus @xmath21 cases , and the results are consistent to better than the 68% confidence intervals . the agreement between the sets of results for the scalar spectral index in particular is excellent . however , for the other three parameters plotted , @xmath66 , @xmath37 and @xmath50 , the agreement is less impressive ; the differences in the recovered values of @xmath37 and @xmath50 are driven by the change in @xmath66 . the peak in the likelihood distributions for the cmb only and cmb plus 2dfgrs @xmath21 cases are in good agreement , as remarked upon in section  3 . there is a clear discrepancy , however , with the preferred parameter values when using cmb data plus the sdss @xmath21 . this is most marked for the physical density of dark matter , @xmath66 . cole et  al . ( 2005 ) noted that the sdss @xmath21 has a slightly bluer slope than that of the 2dfgrs , favouring higher values of @xmath67 . there are two other notable discrepancies between the results obtained with the sdss and 2dfgrs @xmath21 in our basic - six plus one additional free parameter models . when the assumption of a flat universe is relaxed , we find that the constraints on @xmath33 are weaker in the sdss case , @xmath68 ; the allowed range is nearly twice as broad as in the case of the 2dfgrs @xmath21 . this is because on the scales used in our analysis , the sdss power spectrum does a poorer job of constraining @xmath67 compared with the 2dfgrs @xmath21 , and hence is not as effective at breaking the geometrical degeneracy . in the basic - six plus dark energy equation of state parameter set , we find @xmath69 using the sdss @xmath21 , much higher than we found in the case of the 2dfgrs @xmath21 and inconsistent with a cosmological constant . if we also include the snia data from riess et  al . ( 2004 ) , then we obtain a value for the equation of state that is consistent with our previous results : @xmath70 . again , the discrepancy in the result for the equation of state can be traced back to the preferred values of @xmath66 . we note that mactavish et  al . ( 2005 ) find similar results to ours for the equation of state of the dark energy using the sdss galaxy power spectrum . 8 shows the degeneracy in the @xmath71 plane for cmb data alone . adding information from the galaxy power spectrum breaks this degeneracy . if the galaxy @xmath21 data prefer a high value of @xmath67 , as is the case for the sdss data , then a high value of @xmath45 will result .    it may be that these differences between 2dfgrs and sdss amount to no more than an unlucky amount of cosmic variance , but clearly it would be more reassuring if the results showed greater consistency . it will therefore be important to see each dataset subjected to analysis by a variety of algorithms and codes , as happened following the percival et  al . ( 2001 ) 2dfgrs power - spectrum analysis ( tegmark , zaldarriaga & hamilton 2001 ) . this older comparison found consistent results , but the comparison will now be more demanding , given the smaller errors arising from current datasets . we have placed new constraints on the values of the basic cosmological parameters , using an up - to - date compilation of cmb data and the galaxy power spectrum measured from the final 2dfgrs by cole et  al . we have carried out a comprehensive exploration of parameter space , considering five , six and seven parameter models , making different assumptions about the priors used for certain parameters . our main results can be summarized as follows :    * a model in which five parameters are allowed to vary does a remarkably good job of describing the currently available cmb and lss data . * there is an impressive level of agreement between the results obtained for cmb data alone and for cmb data plus the 2dfgrs power spectrum data . if the 2dfgrs @xmath21 is replaced by the sdss @xmath21 , there is some tension between the parameter values preferred by the cmb and sdss datasets . * for some parameters , for example the physical density of dark matter , hubble s constant and the amplitude of density fluctuations , there is a significant tightening of the allowed range of parameter space when the 2dfgrs @xmath21 is included in the analysis . in particular , we infer a density significantly below @xmath72 . * we find some evidence for a departure from a scale invariant primordial spectrum of scalar fluctuations . our results for the scalar perturbation spectral index are only marginally consistent with the scale invariant value @xmath6 ; this spectrum is formally excluded at the @xmath7 confidence level . however , this conclusion is weakened if we drop the assumption that the universe is flat or allow neutrinos to have a mass . * we place new limits on the mass fraction of massive neutrinos : @xmath9 and @xmath10  ev at the 95% level . * several parameters are sensitive to the choice of prior for the optical depth to the last scattering surface , @xmath55 . * we find that a wide range of closed universes are consistent with the cmb data . this range is restricted if we also consider the 2dfgrs @xmath21 data . if we further assume a prior of @xmath73 , then the preferred spatial curvature is close to flat . * we confirm the evidence previously reported by efstathiou et  al . ( 2002 ) for a non - zero dark energy contribution to the energy - density of the universe . * we find a redshift - independent equation of state for the dark energy of @xmath74 , consistent with a cosmological constant . * inflationary models with a scalar field potential with a @xmath75 term are ruled out by our analysis . the final message of this analysis is that meaningful comparison of the parameter constraints from different studies requires a clear listing of the free parameters and their prior distributions . although current datasets measure many parameter combinations extremely well , important degeneracies remain . as we have discussed , there is a good chance that current measurements may be poised on the brink of rejecting the simplest 5-parameter model in favour of something more complicated . however , even if this step is taken , it will require much work before any such deviation from the standard model could have a unique interpretation . we would like to thank sarah bridle for her kind and invaluable help and useful discussions and the referee , andrew jaffe , for a constructive report . we also aknowledge andrew liddle for discussions about bayesian evidence . ags acknowledges the hospitality of the department of physics at the university of durham where part of this work was carried out ; he would also like to thank the scientists throughout the world who submit their articles to the arxiv preprint data base , thereby making them freely available to scientists in developing countries . ags acknowledges a fellowship from conicet ; cmb is funded by a royal society university research fellowship ; jap holds a pparc senior research fellowship ; wjp acknowledges receipt of a pparc fellowship ; ndp is funded by fondecyt project number 3040038 ; pn acknowledges receipt of a eth zwicky fellowship . this work was supported by the european commission s alfa - ii programme through its funding of the latin - american european network for astrophysics and cosmology , lenac , and by pparc . abazajian k. et  al . , 2005 , aj , 129 , 1755
we derive constraints on cosmological parameters using the power spectrum of galaxy clustering measured from the final two - degree field galaxy redshift survey ( 2dfgrs ) and a compilation of measurements of the temperature power spectrum and temperature - polarization cross - correlation of the cosmic microwave background radiation . 
 we analyse a range of parameter sets and priors , allowing for massive neutrinos , curvature , tensors and general dark energy models . in all cases , 
 the combination of datasets tightens the constraints , with the most dramatic improvements found for the density of dark matter and the energy - density of dark energy . 
 if we assume a flat universe , we find a matter density parameter of @xmath0 , a baryon density parameter of @xmath1 , a hubble constant of @xmath2 , a linear theory matter fluctuation amplitude of @xmath3 and a scalar spectral index of @xmath4 ( all errors show the 68% interval ) . 
 our estimate of @xmath5 is only marginally consistent with the scale invariant value @xmath6 ; this spectrum is formally excluded at the @xmath7 confidence level . 
 however , the detection of a tilt in the spectrum is sensitive to the choice of parameter space . if we allow the equation of state of the dark energy to float , we find @xmath8 , consistent with a cosmological constant . 
 we also place new limits on the mass fraction of massive neutrinos : @xmath9 at the 95% level , corresponding to @xmath10  ev . 
 large scale structure of the universe - cosmic microwave background , cosmological parameters