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1.
We compute the redshift space power spectrum of two X-ray cluster samples: the X-ray Brightest Abell Cluster Sample (XBACS) and the Brightest Cluster Sample (BCS) using the method developed by Feldman, Kaiser & Peacock. The power spectra derived for these samples are in agreement with determinations of other optical and X-ray cluster samples. For XBACS we find the largest power spectrum amplitude expected, given the high richness of this sample ( R ≥2) . In the range 0.05< k <0.4  h  Mpc−1 the power spectrum shows a power-law behaviour P ( k )∝ k n with an index n ≃−1.2 . In a similar range, 0.04< k <0.3  h  Mpc−1 , the BCS power spectrum has a smaller amplitude with index n ≃−1.0 . We do not find significant evidence for a peak at k ≃0.05  h  Mpc−1 , suggesting that claims such of feature detections in some cluster samples could rely on artificial inhomogeneities of the data. We compare our results with power spectrum predictions derived by Moscardini et al. within current cosmological models (LCDM and OCDM). For XBACS we find that both models underestimate the amplitude of the power spectrum but for BCS there is reasonably good agreement at k ≳0.03  h  Mpc−1 for both models.  相似文献   

2.
We determine the companion galaxy luminosity function (LF) for regions around isolated spiral galaxies. If we assume that any excess in the galaxy number counts in the vicinity of a spiral galaxy is due to galaxies at the same distance, then a system LF can be determined from the variation of excess numbers with apparent magnitude. By studying the excess over many field 'centre' galaxies, a good statistical accuracy can be obtained for the companion galaxy LF. Since redshift information is not required for the faint galaxies, it is possible to sample further down the LF as compared with redshift surveys. For 23 primary galaxies of known redshift, we find a dwarf satellite Schechter LF with a characteristic magnitude M V *( D )≃−19 and a faint-end slope α=−1.7, down to MV =−14 ( H 0=50 km s−1 Mpc−1).  相似文献   

3.
We present an analysis of the redshift-space power spectrum, P ( k ), of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that P ( k ) can be approximated by a power law, P ( k )∝ kn , with n ≈−1.6 over the wavenumber range 0.04< k <0.1 h Mpc−1. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution, but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale k ∼0.03 h Mpc−1. We compare the power spectra estimated from simulated APM cluster catalogues with those estimated directly from cubical N -body simulation volumes, and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers k ≳0.02 h Mpc−1. These results suggest that the observed turnover in the power spectrum may be a real feature of the cluster distribution, and that we have detected the transition to a near-scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turnover in the cluster power spectrum is in good agreement with the scale of the turnover observed in the power spectrum of APM galaxies.  相似文献   

4.
We produce mock angular catalogues from simulations with different initial power spectra to test methods that recover measures of clustering in three dimensions, such as the power spectrum, variance and higher order cumulants. We find that the statistical properties derived from the angular mock catalogues are in good agreement with the intrinsic clustering in the simulations. In particular, we concentrate on the detailed predictions for the shape of the power spectrum, P ( k ). We find that there is good evidence for a break in the galaxy P ( k ) at scales in the range 0.02< k <0.06 h Mpc−1, using an inversion technique applied to the angular correlation function measured from the APM Galaxy Survey. For variants on the standard cold dark matter (CDM) model, a fit at the location of the break implies Ω h =0.45±0.10, where Ω is the ratio of the total matter density to the critical density, and Hubble's constant is parametrized as H 0=100 h km s−1 Mpc−1. On slightly smaller, though still quasi-linear scales, there is a feature in the APM power spectrum where the local slope changes appreciably, with the best match to CDM models obtained for Ω h ≃0.2. Hence the location and narrowness of the break in the APM power spectrum combined with the rapid change in its slope on quasi-linear scales cannot be matched by any variant of CDM, including models that have a non-zero cosmological constant or a tilt to the slope of the primordial P ( k ). These results are independent of the overall normalization of the CDM models or any simple bias that exists betwen the galaxy and mass distributions.  相似文献   

5.
A class of spatially flat models with cold dark matter (CDM), a cosmological constant and a broken-scale-invariant (BSI) step-like primordial (initial) spectrum of adiabatic perturbations, generated in an exactly solvable inflationary model where the inflaton potential has a rapid change of its first derivative at some point, is confronted with existing observational data on angular fluctuations of the CMB temperature, galaxy clustering and peculiar velocities of galaxies. If we locate the step in the initial spectrum at k  ≃ 0.05  h Mpc−1, where a feature in the spectrum of Abell clusters of galaxies was found that could reflect a property of the initial spectrum, and if the large-scale flat plateau of the spectrum is normalized according to the COBE data, the only remaining parameter of the spectrum is p — the ratio of amplitudes of the metric perturbations between the small-scale and large-scale flat plateaux. Allowed regions in the plane of parameters (Ω = 1 − ΩΛ,  H 0) satisfying all data have been found for p lying in the region (0.8–1.7). Especially good agreement of the form of the present power spectrum in this model with the form of the cluster power spectrum is obtained for the inverted step ( p  < 1,  p  = 0.7–0.8), when the initial spectrum has slightly more power on small scales.  相似文献   

6.
We estimate the two- and three-dimensional power spectra, P 2( K ) and P 3( k ), of the galaxy distribution by applying a maximum likelihood estimator to pixel maps of the APM Galaxy Survey. The analysis provides optimal estimates of the power spectra and of their covariance matrices if the fluctuations are assumed to be Gaussian. Our estimates of P 2( K ) and P 3( k ) are in good agreement with previous work, but we find that the errors at low wavenumbers have been underestimated in some earlier studies. If the galaxy power spectrum is assumed to have the same shape as the mass power spectrum, then the APM maximum likelihood P 3( k ) estimates at k ≤0.19  h  Mpc−1 constrain the amplitude and shape parameter of a scale-invariant CDM model to lie within the 2 σ ranges 0.74≤( σ 8)g≤1.28 and 0.06≤Γ≤0.46 . Using the Galactic extinction estimates of Schlegel, Finkbeiner & Davis, we show that Galactic obscuration has a negligible effect on galaxy clustering over most of the area of the APM Galaxy Survey.  相似文献   

7.
We analyse scale dependence of redshift-space bias b and β  ≡ Ωm0.6/ b in the context of the halo model. We show that linear bias is a good approximation only on large scales, for k <0.1  h  Mpc−1 . On intermediate scales the virial motions of galaxies cause a suppression of the power spectrum relative to the linear one and the suppression differs from the same effect in dark matter. This can potentially mimic the effect of massive neutrinos, and the degeneracy can only be broken if the power spectrum is measured for k ≪0.1  h  Mpc−1 . Different methods to determine β converge for k <0.1  h  Mpc−1 , but give drastically different results on smaller scales, which explains some of the trends observed in the real data. We also assess the level of stochasticity by calculating the cross-correlation coefficient between the reconstructed velocity field divergence and the galaxies, and show that the two fields decorrelate for k >0.1  h  Mpc−1 . Most problematic are galaxies predominantly found in groups and clusters, such as bright, red or elliptical galaxies, where we find poor convergence to a constant bias or β even on large scales.  相似文献   

8.
We allow a more general (step-function) form of the primordial power spectrum than the usual featureless power-law Harrison–Zeldovich (with spectral index   n =1)  power spectrum, and fit it to the latest cosmic microwave background data sets. Although the best-fitting initial power spectrum can differ significantly from the power-law shape, and contains a dip at scales   k ∼0.003  h  Mpc-1  , we find that  Ωm≈0.24  , consistent with previous analyses that assume power-law initial fluctuations. We also explore the feasibility of the early releases of the 2dF and Sloan Digital Sky Survey (SDSS) galaxy redshifts surveys to see these features, and we find that even if features exist in the primordial power spectrum, they are washed out by the window functions of the redshift surveys on scales   k <0.03  h  Mpc-1  .  相似文献   

9.
We report a measurement of the real-space (not redshift-space) power spectrum of galaxies over four and a half decades of wavenumber, 0.01 to 300  h  Mpc−1, from the IRAS Point Source Catalog Redshift Survey (PSC z ). Since estimates of power are highly correlated in the non-linear regime, we also report results for the pre-whitened power spectrum, which is less correlated. The inferred bias between optically selected APM and IRAS -selected PSC z galaxies is about 1.15 at linear scales ≲0.3  h  Mpc−1, increasing to about 1.4 at non-linear scales ≳1  h  Mpc−1. The non-linear power spectrum of PSC z shows a near power-law behaviour to the smallest scales measured, with possible mild upward curvature in the broad vicinity of   k ∼2  h  Mpc−1  . Contrary to the prediction of unbiased dark matter models, there is no prominent inflection at the linear to non-linear transition scale, and no turnover at the transition to the virialized regime. The non-linear power spectrum of PSC z requires scale-dependent bias: all Dark Matter models without scale-dependent bias are ruled out with high confidence.  相似文献   

10.
We present the first optimal power spectrum estimation and three-dimensional deprojections for the dark and luminous matter and their cross-correlations. The results are obtained using a new optimal fast estimator, deprojected using minimum variance and Singular Value Decomposition (SVD) techniques. We show the resulting 3D power spectra for dark matter and galaxies, and their covariance for the VIRMOS-DESCART weak lensing shear and galaxy data. The survey is most sensitive to non-linear scales   k NL∼ 1 h Mpc−1  . On these scales, our 3D power spectrum of dark matter is in good agreement with the RCS 3D power spectrum found by Tegmark & Zaldarriaga. Our galaxy power is similar to that found by the 2MASS survey, and larger than that of SDSS, APM and RCS, consistent with the expected difference in galaxy population.
We find an average bias   b = 1.24 ± 0.18  for the I -selected galaxies, and a cross-correlation coefficient   r = 0.75 ± 0.23  . Together with the power spectra, these results optimally encode the entire two point information about dark matter and galaxies, including galaxy–galaxy lensing. We address some of the implications regarding galaxy haloes and mass-to-light ratios. The best-fitting 'halo' parameter   h ≡ r / b = 0.57 ± 0.16  , suggesting that dynamical masses estimated using galaxies systematically underestimate total mass.
Ongoing surveys, such as the Canada–France–Hawaii Telescope Legacy Survey, will significantly improve on the dynamic range, and future photometric redshift catalogues will allow tomography along the same principles.  相似文献   

11.
It has been known for a long time that the clustering of galaxies changes as a function of galaxy type. This galaxy bias acts as a hindrance to the extraction of cosmological information from the galaxy power spectrum or correlation function. Theoretical arguments show that a change in the amplitude of the clustering between galaxies and mass on large scales is unavoidable, but cosmological information can be easily extracted from the shape of the power spectrum or correlation function if this bias is independent of scale. Scale-dependent bias is generally small on large scales,   k < 0.1  h  Mpc−1  , but on smaller scales can affect the recovery of  Ωm h   from the measured shape of the clustering signal, and have a small effect on the Baryon Acoustic Oscillations. In this paper, we investigate the transition from scale-independent to scale-dependent galaxy bias as a function of galaxy population. We use the Sloan Digital Sky Survey Data Release 5 sample to fit various models, which attempt to parametrize the turn-off from scale-independent behaviour. For blue galaxies, we find that the strength of the turn-off is strongly dependent on galaxy luminosity, with stronger scale-dependent bias on larger scales for more luminous galaxies. For red galaxies, the scale dependence is a weaker function of luminosity. Such trends need to be modelled in order to optimally extract the information available in future surveys, and can help with the design of such surveys.  相似文献   

12.
A key prediction of cosmological theories for the origin and evolution of structure in the Universe is the existence of a 'Doppler peak' in the angular power spectrum of cosmic microwave background (CMB) fluctuations. We present new results from a study of recent CMB observations which provide the first strong evidence for the existence of a 'Doppler peak' localized in both angular scale and amplitude. This first estimate of the angular position of the peak is used to place a new direct limit on the curvature of the Universe, corresponding to a density of Ω = 0.7+0.8−0.5, consistent with a flat universe. Very low-density 'open' universe models are inconsistent with this limit unless there is a significant contribution from a cosmological constant. For a flat standard cold dark matter dominated universe we use our results in conjunction with big bang nucleosynthesis constraints to determine the value of the Hubble constant as H 0 = 30 − 70 km s−1 Mpc−1 for baryon fractions Ωb = 0.05 to 0.2. For H 0 = 50 km s−1 Mpc−1 we find the primordial spectral index of the fluctuations to be n  = 1.1 ± 0.1, in close agreement with the inflationary prediction of n  ≃ 1.0.  相似文献   

13.
We report on the discovery of a narrow-emission-line object at z  = 0.672 detected in a deep ASCA survey. The object, AXJ 0341.4–4453, has a flux in the 2–10 keV band of 1.1 ± 0.27 × 10−13 erg s−1 cm−2, corresponding to a luminosity of 1.8 × 1044 erg s−1 ( q 0 = 0.5, H 0 = 50 km s−1 Mpc−1). It is also marginally detected in the ROSAT 0.5–2 keV band with a flux 5.8 × 10−15 erg s−1 cm−2. Both the ASCA data alone and the combined ROSAT/ASCA data show a very hard X-ray spectrum, consistent with either a flat power law (α < 0.1) or photoelectric absorption with a column of n H > 4 × 1022 cm−2 (α = 1). The optical spectrum shows the high-ionization, narrow emission lines typical of a Seyfert 2 galaxy. We suggest that this object may be typical of the hard sources required to explain the remainder of the X-ray background at hard energies.  相似文献   

14.
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15.
Adams et al. have noted that according to our current understanding of the unification of fundamental interactions, there should have been phase transitions associated with spontaneous symmetry breaking during the inflationary era. This may have resulted in the breaking of scale-invariance of the primordial density perturbation for brief periods. A possible such feature was identified in the power spectrum of galaxy clustering in the automated plate measurement (APM) survey at the scale k  ∼ 0.1  h  Mpc − 1 and it was shown that the secondary acoustic peaks in the power spectrum of the cosmic microwave background (CMB) anisotropy should consequently be suppressed. We demonstrate that this prediction is confirmed by the recent Boomerang and Maxima observations, which favour a step-like spectral feature in the range k  ∼ (0.06–0.6)  h  Mpc − 1 , independently of the similar previous indication from the APM data. Such a spectral break enables an excellent fit to both APM and CMB data with a baryon density consistent with the big bang nucleosynthesis (BBN) value. It also allows the possibility of a matter-dominated universe with zero cosmological constant, which we show can now account for even the evolution of the abundance of rich clusters.  相似文献   

16.
We present a measurement of the K -band luminosity function (LF) of field galaxies obtained from near-infrared imaging of a sample of 345 galaxies selected from the Stromlo-APM Redshift Survey. The LF is reasonably well fitted over the 10-mag range −26 M K −16 by a Schechter function with parameters α =−1.16±0.19, M *=−23.58±0.42 and φ *=0.012±0.008 Mpc−3, assuming a Hubble constant of H 0=100 km s−1 Mpc−1. We have also estimated the LF for two subsets of galaxies subdivided by the equivalent width of the H α emission line at EW(H α )=10 Å. There is no significant difference in LF shape between the two samples, although there is a hint (∼1 σ significance) that emission-line galaxies (ELGs) have M * roughly 1 mag fainter than non-ELGs. Contrary to the optical LF, there is no difference in faint-end slope α between the two samples.  相似文献   

17.
We present a new determination of the local volume-averaged star formation rate from the 1.4-GHz luminosity function of star forming galaxies. Our sample, taken from the   B ≤12  Revised Shapley–Ames catalogue (231 normal spiral galaxies over an effective area of 7.1 sr) has ≃100 per cent complete radio detections and is insensitive to dust obscuration and cirrus contamination. After removal of known active galaxies, the best-fitting Schechter function has a faint-end slope of  −1.27±0.07  in agreement with the local H α luminosity function, characteristic luminosity   L ∗=(2.6±0.7)×1022 W Hz−1  and density   φ ∗=(4.8±1.1)×10−4 Mpc−3.  The inferred local radio luminosity density of  (1.73±0.37±0.03)×1019 W Hz−1 Mpc−3  (Poisson noise, large-scale structure fluctuations) implies a volume-averaged star formation rate ∼2 times larger than the Gallego et al. H α estimate, i.e.   ρ 1.4 GHz=(2.10±0.45±0.04)×10−2 M⊙ yr−1 Mpc−3  for a Salpeter initial mass function from  0.1–125 M⊙  and Hubble constant of 50 km s−1 Mpc−1. We demonstrate that the Balmer decrement is a highly unreliable extinction estimator, and argue that optical–ultraviolet (UV) star formation rates (SFRs) are easily underestimated, particularly at high redshift.  相似文献   

18.
We investigate the effect of primordial non-Gaussianity of the local f NL type on the auto- and cross-power spectra of dark matter haloes using simulations of the Λ cold dark matter cosmology. We perform a series of large N -body simulations of both positive and negative f NL, spanning the range between 10 and 100. Theoretical models predict a scale-dependent bias correction  Δ b ( k , f NL)  that depends on the linear halo bias   b ( M )  . We measure the power spectra for a range of halo mass and redshifts covering the relevant range of existing galaxy and quasar populations. We show that auto- and cross-correlation analyses of bias are consistent with each other. We find that for low wavenumbers with   k < 0.03  h  Mpc−1  the theory and the simulations agree well with each other for biased haloes with   b ( M ) > 1.5  . We show that a scale-independent bias correction improves the comparison between theory and simulations on smaller scales, where the scale-dependent effect rapidly becomes negligible. The current limits on f NL from Slosar et al. come mostly from very large scales   k < 0.01  h  Mpc−1  and, therefore, remain valid. For the halo samples with   b ( M ) < 1.5 − 2  , we find that the scale-dependent bias from non-Gaussianity actually exceeds the theoretical predictions. Our results are consistent with the bias correction scaling linearly with f NL.  相似文献   

19.
We present an X-ray spectroscopic study of the prototype far-infrared galaxy NGC 6240 from ASCA . The soft X-ray spectrum (below 2 keV) shows clear signatures of thermal emission well described by a multitemperature optically thin plasma, which probably originates in a powerful starburst. Strong hard X-ray emission is also detected with ASCA and its spectrum above 3 keV is extremely flat with a prominent iron K line complex, very similar to that seen in the Seyfert 2 galaxy NGC 1068 but about an order of magnitude more luminous ( L 3−10keV ≈ 1.4 × 1042 erg s−1). The hard X-ray spectrum indicates that only reflected X-rays of an active galactic nucleus (AGN) buried in a heavy obscuration ( N H > 2 × 1024 cm−2) are visible. This is evidence for an AGN in NGC 6240, emitting possibly at a quasar luminosity (∼ 1045 erg s−1), and suggests its significant contribution to the far-infrared luminosity.  相似文献   

20.
We determine the underlying shapes of spiral and elliptical galaxies in the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) from the observed distribution of projected galaxy shapes, taking into account the effects of dust extinction and reddening. We assume that the underlying shapes of spirals and ellipticals are well approximated by triaxial ellipsoids. The elliptical galaxy data are consistent with oblate spheroids, with a correlation between luminosity and ellipticity: the mean values of minor to middle axis ratios are 0.41 ± 0.03 for   M r ≈−18  ellipticals and 0.76 ± 0.04 for   M r ≈−22.5  ellipticals. Ellipticals show almost no dependence of axial ratio on galaxy colour, implying a negligible dust optical depth.
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of  ln( e ) =−2.33 ± 0.79  . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E 0 in spiral galaxies is   E 0≃ 0.45  mag for galaxies of median colours, increasing to   E 0= 1  mag for   g − r > 0.9  and   E 0= 1.9  for the luminous and most compact galaxies, with half-light radii  <2  h −1 kpc  .  相似文献   

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