32 research outputs found
The 2dF QSO Redshift Survey - XII. The spectroscopic catalogue and luminosity function
We present the final catalogue of the 2dF QSO Redshift Survey (2QZ), based on Anglo-Australian Telescope 2dF spectroscopic observations of 44 576 colour-selected (ubJr) objects with 18.2
The 2dF QSO Redshift Survey - IV. The QSO power spectrum from the 10k catalogue
We present a power spectrum analysis of the 10k catalogue from the 2dF QSO Redshift Survey. Although the Survey currently has a patchy angular selection function, we use the Virgo Consortium's Hubble Volume simulation to demonstrate that we are able to make a useful first measurement of the power spectrum over a wide range of scales. We compare the redshift-space power spectra of QSOs with those measured for galaxies and Abell clusters at low redshift and find that they show similar shapes in their overlap range, , with . The amplitude of the QSO power spectrum at is almost comparable to that of galaxies at the present day if and (the Λ cosmology), and a factor of ≈ 3 lower if (the EdS cosmology) is assumed. The amplitude of the QSO power spectrum is a factor of ≈ 10 lower than that measured for Abell clusters at the present day. At larger scales, the QSO power spectra continue to rise robustly to ≈ 400 h1 Mpc, implying more power at large scales than in the APM galaxy power spectrum measured by Baugh & Efstathiou. We split the QSO sample into two redshift bins and find little evolution in the amplitude of the power spectrum, consistent with the result for the QSO correlation function. In models with this represents evidence for a QSO-mass bias that evolves as a function of time. We compare the QSO power spectra with cold dark matter (CDM) models to obtain a constraint on the shape parameter, Γ. For two choices of cosmology , and , , we find that the best-fitting model has . In addition, we have shown that a power spectrum analysis of the Hubble Volume ΛCDM mock QSO catalogues with as input produces a result that is statistically consistent with the data. The analysis of the mock catalogues also indicates that the above results for Γ are unlikely to be dominated by systematic effects, owing to the current catalogue window. We conclude that the form of the QSO power spectrum shows large-scale power significantly in excess of the standard CDM prediction, similar to that seen in local galaxy surveys at intermediate scales
The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function
In this paper we present a clustering analysis of quasi-stellar objects (QSOs) using over 20000 objects from the final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the redshift-space two-point correlation function, ξ(s). When averaged over the redshift range 0.3 < z < 2.2 we find that ξ(s) is flat on small scales, steepening on scales above ~25h-1 Mpc. In a WMAP/2dF cosmology (Ωm= 0.27, ΩΛ= 0.73) we find a best-fitting power law with s0= 5.48+0.42-0.48h-1 Mpc and γ= 1.20 +/- 0.10 on scales s= 1 to 25h-1 Mpc. We demonstrate that non-linear redshift-space distortions have a significant effect on the QSO ξ(s) at scales less than ~10h-1 Mpc. A cold dark matter model assuming WMAP/2dF cosmological parameters is a good description of the QSO ξ(s) after accounting for non-linear clustering and redshift-space distortions, and allowing for a linear bias at the mean redshift of bQ(z= 1.35) = 2.02 +/- 0.07. We subdivide the 2QZ into 10 redshift intervals with effective redshifts from z= 0.53 to 2.48. We find a significant increase in clustering amplitude at high redshift in the WMAP/2dF cosmology. The QSO clustering amplitude increases with redshift such that the integrated correlation function, , within 20h-1 Mpc is and . We derive the QSO bias and find it to be a strong function of redshift with bQ(z= 0.53) = 1.13 +/- 0.18 and bQ(z= 2.48) = 4.24 +/- 0.53. We use these bias values to derive the mean dark matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit approximately the same mass DMHs with MDH= (3.0 +/- 1.6) × 1012h-1 Msolar, which is close to the characteristic mass in the Press-Schechter mass function, M*, at z= 0. These results imply that L*Q QSOs at z~ 0 should be largely unbiased. If the relation between black hole (BH) mass and MDH or host velocity dispersion does not evolve, then we find that the accretion efficiency (L/LEdd) for L*Q QSOs is approximately constant with redshift. Thus the fading of the QSO population from z~ 2 to ~0 appears to be due to less massive BHs being active at low redshift. We apply different methods to estimate, tQ, the active lifetime of QSOs and constrain tQ to be in the range 4 × 106-6 × 108 yr at z~ 2. We test for any luminosity dependence of QSO clustering by measuring ξ(s) as a function of apparent magnitude (equivalent to luminosity relative to L*Q). However, we find no significant evidence of luminosity-dependent clustering from this data set
Cosmic distance-duality as probe of exotic physics and acceleration
In cosmology, distances based on standard candles (e.g. supernovae) and
standard rulers (e.g. baryon oscillations) agree as long as three conditions
are met: (1) photon number is conserved, (2) gravity is described by a metric
theory with (3) photons travelling on unique null geodesics. This is the
content of distance-duality (the reciprocity relation) which can be violated by
exotic physics. Here we analyse the implications of the latest cosmological
data sets for distance-duality. While broadly in agreement and confirming
acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia
at z > 0.5, perhaps due to lensing magnification bias. This brightening has
been interpreted as evidence for a late-time transition in the dark energy but
because it is not seen in the d_A data we argue against such an interpretation.
Our results do, however, rule out significant SN-Ia evolution and extinction:
the "replenishing" grey-dust model with no cosmic acceleration is excluded at
more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby
illustrating the power of distance-duality even with current data sets.Comment: 6 pages, 4 colour figures. Version accepted as a Rapid Communication
in PR
The 2MASS galaxy angular power spectrum: Probing the galaxy distribution to Gigaparsec scales
We present an angular power spectrum analysis of the 2MASS full release
extended source catalogue. The main sample used includes 518,576 galaxies below
an extinction-corrected magnitude of K=13.5 and limited to |b|>20. The power
spectrum results provide an estimate of the galaxy density fluctuations at
extremely large scales, r<1000 Mpc. We compare this with mock predictions
constructed from the LCDM Hubble Volume mock catalogue. We find that over the
range 1<l<100 the 2MASS C_l is steeper than that for the Hubble Volume model.
However, in the linear regime (l<30) there is good agreement between the two.
We investigate in detail the effects of possible sources of systematic error.
Converting linear power spectrum predictions for the form of the
three-dimensional matter power spectrum, P(k), and assuming a flat CDM
cosmology, a primordial n_s=1 spectrum and negligible neutrino mass, we perform
fits to the galaxy angular power spectrum at large linear scales (l<30,
corresponding to r>50 Mpc). We obtain constraints on the galaxy power spectrum
shape of Gamma=0.14+/-0.02, in good agreement with previous estimates inferred
at smaller scales. We also constrain the galaxy power spectrum normalisation to
(sigma_8 b_K)^2=1.36+/-0.10; in combination with previous constraints on
sigma_8 we infer a K-band bias of b_K=1.39+/-0.12. We are also able to provide
weak constraints on Omega_m h and Omega_b/Omega_m. These results are based on
the usual assumption that the errors derived from the Hubble Volume mocks are
applicable to all other models. If we instead assume that the error is
proportional to the C_l amplitude then the constraints weaken; for example it
becomes more difficult to reject cosmologies with lower Gamma.Comment: 10 pages, 8 figures, submitted to MNRA
High-order 2MASS galaxy correlation functions: Probing the primordial density field and the linearity of galaxy bias
We use the 2MASS extended source catalogue to determine angular correlation
functions, w_p, to high orders (p<=9). The main sample contains 650,745
galaxies and represents an order of magnitude increase in solid angle over
previous samples used in such analysis. The high-order correlation functions
are used to determine the projected and real space hierarchical amplitudes, s_p
and S_p. In contrast to recent results, for p<=6 these parameters are found to
be quite constant over a wide range of scales to r=40 Mpc, consistent with a
Gaussian form to the primordial distribution of density fluctuations which has
evolved under the action of gravitational instability. We test the sensitivity
of our results to the presence of rare fluctuations in the local galaxy
distribution by cutting various regions of over-density from the main sample;
unlike previous analyses, we find that our results are relatively robust to the
removal of the largest superclusters. We use our constraints on the K-band S_p
parameters in two ways. First, we examine their consistency with non-Gaussian
initial conditions; we are able to rule out strong non-Gaussianity in the
primordial density field, as might be seeded by topological defects such as
cosmic strings or global textures at the 2.5 sigma confidence level. Second, we
investigate the way in which galaxies trace the underlying mass distribution.
We find evidence for a non-zero quadratic contribution to the galaxy bias,
parameterised by c_2=0.57+/-0.33. This positive result represents a significant
difference from the negative values found previously; we examine a possible
explanation in the light of recent observations which universally provide
negative values for c_2.Comment: 13 pages, 5 figures, submitted to MNRA
2MASS constraints on the local large-scale structure: a challenge to ΛCDM?
We investigate the large-scale structure of the local galaxy distribution using the recently completed 2 Micron All Sky Survey (2MASS) via three techniques. First, we determine the Ks-band number counts over the ≈4000 deg 2 APM survey area where evidence for a large-scale ‘local hole ’ has previously been detected and compare them to a homogeneous prediction. Considering a ΛCDM form for the 2-point angular correlation function, the observed deficiency represents a 5σ fluctuation in the galaxy distribution. We check the model normalisation using faint K-band data compiled from the literature; the normalisation used in this paper is in excellent agreement, and the observed counts over the APM survey area would require the model to be lowered by 3.8σ. However, the issue is complicated by the b �20 ◦ and b �-20 ◦ 2MASS counts which lie below the best-fit model normalisation. Second, since the Ks-band counts over the APM survey area continue to suggest the possible presence of excess clustering over the ΛCDM prediction, we next probe the power at large scales by comparing the 2MASS and ΛCDM mock galaxy angular power spectra. We find a 3σ excess in th
The Durham/UKST Galaxy Redshift Survey - VII. Redshift-space distortions in the power spectrum
We investigate the effect of redshift-space distortions in the power spectrum
parallel and perpendicular to the observer's line of sight, P(k_par,k_perp),
using the optically selected Durham/UKST Galaxy Redshift Survey. On small,
non-linear scales anisotropy in the power-spectrum is dominated by the galaxy
velocity dispersion; the `Finger of God' effect. On larger, linear scales
coherent peculiar velocities due to the infall of galaxies into overdense
regions are the main cause of anisotropy. According to gravitational
instability theory these distortions depend only on the density and bias
parameters via beta. Geometrical distortions also occur if the wrong cosmology
is assumed, although these would be relatively small given the low redshift of
the survey. To quantify these effects, we assume the real-space power spectrum
of the APM Galaxy Survey, and fit a simple model for the redshift-space and
geometrical distortions. Assuming a flat Omega = 1 universe, we find values for
the one-dimensional pairwise velocity dispersion of sigma_p = 410 +- 170 km/s,
and beta = 0.38 +- 0.17. An open Omega = 0.3, and a flat Omega = 0.3, Lambda =
0.7 universe yield sigma_p = 420 km/s, beta = 0.40, and sigma_p = 440 km/s,
beta = 0.45 respectively, with comparable errors. These results are consistent
with estimates using the two-point galaxy correlation function, xi(sigma,pi),
and favour either a low-density universe with Omega ~ 0.3 if galaxies trace the
underlying mass distribution, or a bias factor of b ~ 2.5 if Omega = 1.Comment: 5 pages, accepted for publication in MNRA
2MASS Constraints on the Local Large-Scale Structure: A Challenge to LCDM?
We investigate the large-scale structure of the local galaxy distribution
using the recently completed 2 Micron All Sky Survey (2MASS). First, we
determine the K-band number counts over the 4000 sq.deg. APM survey area where
evidence for a large-scale `local hole' has previously been detected and
compare them to a homogeneous prediction. Considering a LCDM form for the
2-point angular correlation function, the observed deficiency represents a 5
sigma fluctuation in the galaxy distribution. We check the model normalisation
using faint K-band data compiled from the literature; the normalisation used in
this paper is in excellent agreement, and the observed counts over the APM
survey area would require the model to be lowered by 3.8 sigma. However, the
issue is complicated by the b>20 and b<-20 2MASS counts which lie below the
best-fit model normalisation. Second, since the K-band counts over the APM
survey area continue to suggest the possible presence of excess clustering over
the LCDM prediction, we next probe the power at large scales by comparing the
2MASS and LCDM mock galaxy angular power spectra. We find a 3 sigma excess in
the 2MASS catalogue over the LCDM prediction at large scales (l<30). However,
this excess is not enough to account for the low counts over the APM survey
area. Finally, we apply a counts in cells analysis to the 2MASS data and mock
catalogues; on the assumption that the 2MASS catalogue at |b|>20 is
representative, we find excellent agreement between the biased LCDM mocks and
the 2MASS catalogue to 30 deg. The crux of the interpretation of these results
appears to be whether the 2MASS volume is yet big enough to constitute a fair
sample of the Universe. (abridged)Comment: 10 pages, 7 figures. Submitted to MNRA
Non-Voigt Ly Absorption Line Profiles
Recent numerical simulations have lead to a paradigm shift in our
understanding of the intergalactic medium, and the loss of a physical
justification for Voigt profile fitting of the Lyman-alpha forest. Many
individual lines seen in simulated spectra have significant departures from the
Voigt profile, yet could be well fitted by a blend of two or more such lines.
We discuss the expected effect on the line profiles due to ongoing
gravitational structure formation and Hubble expansion. We develop a method to
detect departures from Voigt profiles of the absorption lines in a statistical
way and apply this method to simulated Lyman-alpha forest spectra, confirming
that the profiles seen do statistically differ from Voigt profiles.Comment: Accepted for publication in ApJL. 10 pages, 3 figure