首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
In this paper we have extended the entropy-driven model of cluster evolution developed by Bower in order to be able to predict the evolution of galaxy clusters for a range of cosmological scenarios. We have applied this model to recent measurements of the evolution of the L x− T normalization and X-ray luminosity function in order to place constraints on cosmological parameters. We find that these measurements alone do not select a particular cosmological framework. An additional constraint is required on the effective slope of the power spectrum to break the degeneracy that exists between this and the background cosmology. We therefore include a theoretical calculation of the Ω0 dependence on the power spectrum, based on the cold dark matter paradigm, which infers Ω0<0.55 (0.1<Ω0<0.7 for Ω0+Λ0=1), at the 95 per cent confidence level. Alternatively, an independent measurement of the slope of the power spectrum from galaxy clustering requires Ω0<0.6 (Ω0<0.65 for Ω0+Λ0=1), again to 95 per cent confidence. The rate of entropy evolution is insensitive to the values of Ω0 considered, although it is sensitive to changes in the distribution of the intracluster medium.  相似文献   

2.
The evolution of the abundance of galaxy clusters depends sensitively on the value of the cosmological density parameter, Ω0. Recent ASCA data are used to quantify this evolution as measured by the cluster X-ray temperature function. A χ2 minimization fit to the cumulative temperature function, as well as a maximum-likelihood estimate (which requires additional assumptions about cluster luminosities), leads to the estimate Ω0 ≈ 0.45 ± 0.25 (1σ statistical error). Various systematic uncertainties are considered, none of which significantly enhances the probability that Ω0 = 1. These conclusions hold for models with or without a cosmological constant, i.e., with Λ0 = 0 or Λ0 = 1 − Ω0. The statistical uncertainties are at least as large as any of the individual systematic errors that have been considered here, suggesting that additional temperature measurements of distant clusters will allow an improvement in this estimate. An alternative method that uses the highest redshift clusters to place an upper limit on Ω0 is also presented and tentatively applied, with the result that Ω0  1 can be ruled out at the 98 per cent confidence level. Whilst this method does not require a well-defined statistical sample of distant clusters, there are still modelling uncertainties that preclude a firmer conclusion at this time.  相似文献   

3.
We present a measurement of the cluster X-ray luminosity–temperature ( L – T ) relation out to high redshift ( z ∼0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fitted in redshift and luminosity bins. The resulting temperature and luminosity measurements of these bins, which occupy a region of the high-redshift L – T relation not previously sampled, are compared with existing measurements at low redshift in order to constrain the evolution of the L – T relation. We find the best fit to low-redshift ( z <0.2) cluster data, at T >1 keV, to be L ∝ T 3.15±0.06. Our data are consistent with no evolution in the normalization of the L – T relation up to z ∼0.8. Combining our results with ASCA measurements taken from the literature, we find η =0.19±0.38 (for Ω0=1, with 1 σ errors) where L Bol∝(1+ z ) η T 3.15, or η =0.60±0.38 for Ω0=0.3. This lack of evolution is considered in terms of the entropy-driven evolution of clusters. Further implications for cosmological constraints are also discussed.  相似文献   

4.
We have observed the   z =0.78  cluster MS 1137.5+6625 with the Ryle Telescope (RT) at 15 GHz. After subtraction of contaminating radio sources in the field, we find a Sunyaev–Zel'dovich flux decrement of  -421±60 μJy  on the ≈0.65 k λ baseline of the RT, spatially coincident with the optical and X-ray positions for the cluster core.
For a spherical King-profile cluster model, the best fit to our flux measurement has a core radius   θ C=20 arcsec  , consistent with previous X-ray observations, and a central temperature decrement  Δ T =650±92 μK  .
Using this model, we calculate that the cluster has a gas mass inside a     radius of  2.9×1013 M⊙  for an  Ω M =1  universe and  1.6×1013 M⊙  for  Ω M =0.3  ,  ΩΛ=0.7  . We compare this model with existing measurements of the total mass of the cluster, based on gravitational lensing, and estimate a gas fraction for MS 1137.5+6625 of ≈8 per cent.  相似文献   

5.
We have observed the Sunyaev–Zel'dovich (SZ) effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the Bright Cluster Sample and the Northern ROSAT All-Sky Survey (RASS) cluster catalogues to be well above the surface brightness limit of the RASS, and hence to be unbiased with respect to the orientation of the cluster. This controls a major potential systematic effect in the SZ/X-ray method of measuring H 0. Taking the weighted geometric mean of the results and including the main sources of error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity and substructure of the clusters, we find   H 0= 59+10−9 (random)+8−7(systematic) km s−1 Mpc−1  assuming a standard cold dark matter model with  ΩM= 1.0, ΩΛ= 0.0  or   H 0= 66+11−10 +9−8 km  s−1 Mpc−1  if  ΩM= 0.3, ΩΛ= 0.7  .  相似文献   

6.
We present the observed relation between Δ T SZ, the cosmic microwave background (CMB) temperature decrement due to the Sunyaev–Zeldovich (SZ) effect, and L , the X-ray luminosity of galaxy clusters. We discuss this relation in terms of the cluster properties, and show that the slope of the observed Δ T SZ– L relation is in agreement with both the L – T e relation based on numerical simulations and X-ray emission observations, and the M gas– L relation based on observation. The slope of the Δ T SZ– L relation is also consistent with the M tot– L relation, where M tot is the cluster total mass based on gravitational lensing observations. This agreement may be taken to imply a constant gas mass fraction within galaxy clusters, however, there are large uncertainties, dominated by observational errors, associated with these relations. Using the Δ T SZ– L relation and the cluster X-ray luminosity function, we evaluate the local cluster contribution to arcmin-scale cosmic microwave background anisotropies. The Compton distortion y -parameter produced by galaxy clusters through the SZ effect is roughly two orders of magnitude lower than the current upper limit based on FIRAS observations.  相似文献   

7.
Using the ray-bundle method for calculating gravitational lens magnifications, we outline a method by which the magnification probability may be determined specifically in the weak lensing limit for cosmological models obtained from N -body simulations.
16 different models are investigated, which are variations on three broad classes of cold dark matter model: the standard model with  (Ω0, λ 0)=(1.0,0.0)  , the open model with  (Ω0, λ 0)=(0.3,0.0)  and the lambda model, which is a flat model with a cosmological constant  (Ω0, λ 0)=(0.3,0.7)  .
The effects of varying the Hubble parameter, H 0, the power spectrum shape parameter, Γ, and the cluster mass normalization, σ 8, are studied. It is shown that there is no signature of these parameters in the weak lensing magnification distributions. The magnification probability distributions are also shown to be independent of the numerical parameters such as the lens mass and simulation box size in the N -body simulations.  相似文献   

8.
The number density of rich galaxy clusters still provides the most robust way of normalizing the power spectrum of dark matter perturbations on scales relevant to large-scale structure. We revisit this constraint in the light of several recent developments: (1) the availability of well-defined samples of local clusters with relatively accurate X-ray temperatures; (2) new theoretical mass functions for dark matter haloes, which provide a good fit to large numerical simulations; (3) more accurate mass–temperature relations from larger catalogues of hydrodynamical simulations; (4) the requirement to consider closed as well as open and flat cosmologies to obtain full multiparameter likelihood constraints for CMB and SNe studies. We present a new sample of clusters drawn from the literature and use this sample to obtain improved results on σ 8, the normalization of the matter power spectrum on scales of 8  h −1 Mpc, as a function of the matter density and cosmological constant in a universe with general curvature. We discuss our differences with previous work, and the remaining major sources of uncertainty. Final results on the normalization, approximately independent of power spectrum shape, can be expressed as constraints on σ at an appropriate cluster normalization scale R Cl. We provide fitting formulas for R Cl and σ ( R Cl) for general cosmologies, as well as for σ 8 as a function of cosmology and shape parameter Γ. For flat models we find approximately σ 8≃(0.495−0.037+0.034)ΩM−0.60 for Γ=0.23, where the error bar is dominated by uncertainty in the mass–temperature relation.  相似文献   

9.
We present a correlation function analysis for the catalogue of photometric redshifts obtained from the Hubble Deep Field image by Fernandez-Soto, Lanzetta & Yahil. By dividing the catalogue into redshift bins of width Δ z =0.4 we measured the angular correlation function w ( θ ) as a function of redshift up to z ∼4.8. From these measurements we derive the trend of the correlation length r 0. We find that r 0( z ) is roughly constant with look-back time up to z ≃2, and then increases to higher values at z ≳2.4. We estimate the values of r 0, assuming ξ ( r , z )=[ r r 0( z )]− γ , γ =1.8 and various geometries. For Ω0=1 we find r 0( z =3)≃7.00±4.87  h −1 Mpc, in good agreement with the values obtained from analysis of the Lyman break galaxies.  相似文献   

10.
We study the peculiar velocity field inferred from the Mark III spirals using a new method of analysis. We estimate optimal values of Tully–Fisher scatter and zero-point offset, and we derive the three-dimensional rms peculiar velocity ( σ v ) of the galaxies in the samples analysed. We check our statistical analysis using mock catalogues derived from numerical simulations of cold dark matter (CDM) models considering measurement uncertainties and sampling variations. Our best determination for the observations is σ v =(660±50) km s−1. We use the linear theory relation between σ v , the density parameter Ω, and the galaxy correlation function ξ ( r ) to infer the quantity     , where b is the linear bias parameter of optical galaxies and the uncertainties correspond to bootstrap resampling and an estimated cosmic variance added in quadrature. Our findings are consistent with the results of cluster abundances and redshift-space distortion of the two-point correlation function. These statistical measurements suggest a low value of the density parameter Ω∼0.4 if optical galaxies are not strongly biased tracers of mass.  相似文献   

11.
We analyse the spatial clustering properties of the ROSAT All-Sky Survey (RASS) 1 Bright Sample, an X-ray flux-limited catalogue of galaxy clusters selected from the southern part of the survey. The two-point correlation function ( r ) of the whole sample is well fitted (in an Einsteinde Sitter model) by the power law =( r r 0) , with and (95.4 per cent confidence level with one fitting parameter). We use the RASS 1 Bright Sample as a first application of a theoretical model that aims to predict the clustering properties of X-ray clusters in flux-limited surveys for different cosmological scenarios. The model uses the theoretical and empirical relations between mass, temperature and X-ray cluster luminosity, and fully accounts for the redshift evolution of the underlying dark matter clustering and cluster bias factor. The comparison between observational results and theoretical predictions shows that the Einsteinde Sitter models display too low a correlation length, while models with a matter density parameter 0m=0.3 (with or without a cosmological constant) are successful in reproducing the observed clustering. The dependence of the correlation length r 0 on the X-ray limiting flux and luminosity of the sample is generally consistent with the predictions of all our models. Quantitative agreement is however only reached for 0m=0.3 models. The model presented here can be reliably applied to future deeper X-ray cluster surveys: the study of the clustering properties will provide a useful complementary tool to the traditional cluster abundance analyses used to constrain the cosmological parameters.  相似文献   

12.
We discuss the constraints that future photometric and spectroscopic redshift surveys can put on dark energy through the baryon oscillations of the power spectrum. We model the dark energy either with a perfect fluid or a scalar field and take into account the information contained in the linear growth function. We show that the growth function helps to break the degeneracy in the dark energy parameters and reduce the errors on   w 0, w 1  roughly by 30 per cent, making more appealing multicolour surveys based on photometric redshifts. We find that a 200-deg2 spectroscopic survey reaching   z ≈ 3  can constrain   w 0, w 1  to within  Δ w 0= 0.21, Δ w 1= 0.26  , to  Δ w 0= 0.39, Δ w 1= 0.54  using photometric redshifts with an absolute uncertainty of 0.02, and to  Δ w 0= 0.43, Δ w 1= 0.66  with an uncertainty of 0.04. In the scalar field case, we show that the slope n of the inverse power-law potential for dark energy can be constrained to  Δ n = 0.26  (spectroscopic redshifts) or  Δ n = 0.40  (photometric redshifts), i.e. better than with future ground-based supernovae surveys or cosmic microwave background data.  相似文献   

13.
A combined sample of 79 high- and low-redshift Type Ia supernovae (SNe) is used to set constraints on the degree of anisotropy in the Universe out to z ≃1. First, we derive the global most probable values of matter density ΩM, the cosmological constant ΩΛ and the Hubble constant H 0, and find them to be consistent with the published results from the two data sets of Riess et al. and Perlmutter et al. We then examine the Hubble diagram (HD, i.e., the luminosity–redshift relation) in different directions on the sky by utilizing spherical harmonic expansion. In particular, via the analysis of the dipole anisotropy, we divide the sky into the two hemispheres that yield the most discrepant of the three cosmological parameters, and the scatter χ HD2 in each case. The most discrepant values roughly move along the locus −4ΩM+3ΩΛ=1 (cf. Perlmutter et al.), but by no more than Δ≈2.5 along this line. For a perfect Friedmann–Robertson–Walker universe, Monte Carlo realizations that mimic the current set of SNe yield values higher than the measured Δ in ∼1/5 of the cases (for ΩM). We discuss implications for the validity of the Cosmological Principle, and possible calibration problems in the SNe data sets.  相似文献   

14.
Recently, Park &38; Gott claimed that there is a statistically significant, strong, negative correlation between the image separation Δθ and source redshift z s for gravitational lenses. This is somewhat puzzling if one believes in a flat ( k  = 0) universe, since in this case the typical image separation is expected to be independent of the source redshift, while one expects a negative correlation in a k  = −1 universe and a positive one in a k  = +1 universe. Park &38; Gott explored several effects that could cause the observed correlation, but no combination of these can explain the observations with a realistic scenario. Here, I explore this test further in three ways. First, I show that in an inhomogeneous universe a negative correlation is expected regardless of the value of k . Secondly, I test whether the Δθ– z s relation can be used as a test to determine λ0 and Ω0, rather than just the sign of k . Thirdly, I compare the results of the test from the Park &38; Gott sample with those using other samples of gravitational lenses, which can illuminate (unknown) selection effects and probe the usefulness of the Δθ– z s relation as a cosmological test.  相似文献   

15.
We determine cosmological and evolutionary parameters from the 3CR K -band Hubble diagram and K -band number counts, assuming that the galaxies in question undergo pure luminosity evolution. Separately the two data sets are highly degenerate with respect to choice of cosmological and evolutionary parameters, but in combination the degeneracy is resolved. Of models that either are flat or have  ΩΛ=0  , the preferred ones are close to the canonical case  Ωcold  matter=1  ,  ΩΛ=0  , with luminosity evolution amounting to 1 mag brighter at   z =1  .  相似文献   

16.
We show how the continuity equation can be used to determine pattern speeds in the Milky Way Galaxy (MWG). This method, first discussed by Tremaine & Weinberg in the context of external galaxies, requires projected positions, ( l , b ), and line-of-sight velocities for a spatially complete sample of relaxed tracers. If the local standard of rest (LSR) has a zero velocity in the radial direction ( u LSR), then the quantity that is measured is  Δ V ≡Ωp R 0- V LSR  , where Ωp is the pattern speed of the non-axisymmetric feature, R 0 is the distance of the Sun from the Galactic centre and V LSR is the tangential motion of the LSR, including the circular velocity. We use simple models to assess the reliability of the method for measuring a single, constant pattern speed of either a bar or spiral in the inner MWG. We then apply the method to the OH/IR stars in the ATCA/VLA OH 1612-MHz survey of Sevenster et al., finding  Δ V =252±41 km s-1,  if   u LSR=0  . Assuming further that   R 0=8 kpc  and   V LSR=220 km s-1,  this gives  Ωp=59±5 km s-1 kpc-1  with a possible systematic error of perhaps 10 km s−1 kpc−1. The non-axisymmetric feature for which we measure this pattern speed must be in the disc of the MWG.  相似文献   

17.
The universal baryonic mass fraction  (Ωb/Ωm)  can be sensitively constrained using X-ray observations of galaxy clusters. In this paper, we compare the baryonic mass fraction inferred from measurements of the cosmic microwave background with the gas mass fractions ( f gas) of a large sample of clusters taken from the recent literature. In systems cooler than 4 keV, f gas declines as the system temperature decreases. However, in higher temperature systems, f gas( r 500) converges to  ≈(0.12 ± 0.02)( h /0.72)−1.5  , where the uncertainty reflects the systematic variations between clusters at r 500. This is significantly lower than the maximum-likelihood value of the baryon fraction from the recently released Wilkinson Microwave Anisotropy Probe ( WMAP ) 3-yr results. We investigate possible reasons for this discrepancy, including the effects of radiative cooling and non-gravitational heating, and conclude that the most likely solution is that Ωm is higher than the best-fitting WMAP value (we find  Ωm= 0.36+0.11−0.08  ), but consistent at the 2σ level. Degeneracies within the WMAP data require that σ8 must also be greater than the maximum likelihood value for consistency between the data sets.  相似文献   

18.
We examine the possibility of the decay of the vacuum energy into a homogeneous distribution of a thermalized cosmic microwave background (CMB), which is characteristic of an adiabatic vacuum energy decay into photons. It is shown that observations of the primordial density fluctuation spectrum, obtained from CMB and galaxy distribution data, restrict the possible decay rate. When photon creation due to an adiabatic vacuum energy decay takes place, the standard linear temperature dependence   T ( z ) = T 0(1 + z )  is modified, where T 0 is the present CMB temperature, and can be parametrized by a modified CMB temperature dependence     . From the observed CMB and galaxy distribution data, a strong limit on the maximum value of the decay rate is obtained by placing a maximum value  βmax≃ 3.4 × 10−3  on the β parameter.  相似文献   

19.
We investigate the properties of clusters of galaxies in the ΛCDM models with a step-like initial power spectrum. We examine the mass function, the peculiar velocities and the power spectrum of clusters in models with different values of the density parameter Ω0, the normalized Hubble constant h and the spectral parameter p that describes the shape of the initial power spectrum. The results are compared with observations. We also investigate the rms bulk velocity in the models, where the properties of clusters are consistent with the observed data. We find that the power spectrum of clusters is in good agreement with the observed power spectrum of the Abell–ACO clusters if the spectral parameter p is in the range p =0.6–0.8. The power spectrum and the rms peculiar velocity of clusters are consistent with observations only if Ω0<0.4 . The models with Ω0=0.3 are consistent with the observed properties of clusters if h =0.50–0.63. For h =0.65, we find that Ω0=0.20–0.27.  相似文献   

20.
Recent detections of high-redshift absorption by both atomic hydrogen and molecular gas in the radio spectra of quasars have provided a powerful tool for measuring possible temporal and spatial variations of physical 'constants' in the universe.
We compare the frequency of high-redshift hydrogen 21-cm absorption with that of associated molecular absorption in two quasars to place new (1σ) upper limits on any variation in y≡gpα2 (where α is the fine-structure constant, and gp is the proton g -factor of
   
at redshifts z = 0.25 and 0.68. These quasars are separated by a comoving distance of 3000 Mpc ( H 0= 75 km s−1 Mpc−1 and q 0). We also derive limits on the time rates of change
   
    between the present epoch and z = 0.68. These limits are more than an order of magnitude smaller than previous results derived from high-redshift measurements.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号