arXiv subjects

F. Atrio-Barandela

Publications and source records attributed to F. Atrio-Barandela.

At least 91 records · Page 5Linked to original sources

arXiv2011

Measuring the dark flow with public X-ray cluster data

We present new results on the "dark flow" from a measurement of the dipole in the distribution of peculiar velocities of galaxy clusters, applying the methodology proposed and developed by us earlier. Our latest measurement is conducted using new, low-noise 7-yr WMAP data as well as an all-sky sample of X-ray selected galaxy clusters compiled exclusively from published catalogs. Our analysis of the CMB signature of the kinematic Sunyaev-Zeldovich (SZ) effect finds a statistically significant dipole at the location of galaxy clusters. The residual dipole outside the cluster regions is small, rendering our overall measurement 3-4 sigma significant. The amplitude of the dipole correlates with cluster properties, being larger for the most X-ray luminous clusters, as required if the signal is produced by the SZ effect. Since it is measured at zero monopole, the dipole can not be due to the thermal SZ effect. Our results are consistent with those obtained earlier by us from 5-yr WMAP data and using a proprietary cluster catalog. In addition, they are robust to quadrupole removal, demonstrating that quadrupole leakage contributes negligibly to the signal. The lower noise of the 7-yr WMAP also allows us, for the first time, to obtain tentative empirical confirmation of our earlier conjecture that the adopted filtering flips the sign of the KSZ effect for realistic clusters and thus of the deduced direction of the flow. The latter is consistent with our earlier measurement in both the amplitude and direction. Assuming the filtering indeed flips the sign of the KSZ effect from the clusters, the direction agrees well also with the results of independent work using galaxies as tracers at lower distances. We make all maps and cluster templates derived by us from public data available to the scientific community to allow independent tests of our method and findings.

astro-ph.CO↗

arXiv2010

The error budget of the Dark Flow measurement

We analyze the uncertainties and possible systematics associated with the "Dark Flow" measurements using the cumulative Sunyaev-Zeldovich effect combined with all-sky catalogs of clusters of galaxies. Filtering of all-sky cosmic microwave background (CMB) maps is required to remove the intrinsic cosmological signal down to the limit imposed by cosmic variance. Contributions to the errors come from the remaining cosmological signal, that integrates down with the number of clusters, and the instrumental noise, that scales with the number of pixels; the latter decreases with integration time and is subdominant for the Wilkinson Microwave Anisotropy Probe 5-year data. It is proven both analytically and numerically that the errors for 5-year WMAP data are $\simeq 15\sqrt{3/N_{\rm clusters}} μ$K per dipole component. The measured bulk flow velocity is significant at up to the $>99.95%$ confidence level, depending on the cluster sample. We discuss different methods to compute error bars and demonstrate that they have biases that would overpredict the errors, as is the case in a recent reanalysis of our earlier results. If the signal is caused by systematic effects present in the data, such systematics must have a dipole pattern, which correlates with cluster X-ray luminosity and is present only at cluster positions. Only contributions from the Sunyaev-Zeldovich effect could provide such contaminants via several potential effects. We discuss such candidates apart from the bulk-motion of the cluster samples and demonstrate that their contributions to our measurements are negligible. (abridged)

astro-ph.CO↗

arXiv2010

A new measurement of the bulk flow of X-ray luminous clusters of galaxies

We present new measurements of the large-scale bulk flows of galaxy clusters based on 5-year WMAP data and a significantly expanded X-ray cluster catalogue. Our method probes the flow via measurements of the kinematic Sunyaev-Zeldovich (SZ) effect produced by the hot gas in moving clusters. It computes the dipole in the cosmic microwave background (CMB) data at cluster pixels, which preserves the SZ component while integrating down other contributions. Our improved catalog of over 1,000 clusters enables us to further investigate possible systematic effects and, thanks to a higher median cluster redshift, allows us to measure the bulk flow to larger scales. We present a corrected error treatment and demonstrate that the more X-ray luminous clusters, while fewer in number, have much larger optical depth, resulting in a higher dipole and thus a more accurate flow measurement. This results in the observed correlation of the dipole derived at the aperture of zero monopole with the monopole measured over the cluster central regions. This correlation is expected if the dipole is produced by the SZ effect and cannot be caused by unidentified systematics (or primary cosmic microwave background anisotropies). We measure that the flow is consistent with approximately constant velocity out to at least 800 Mpc. The significance of the measured signal peaks around 500 Mpc, most likely because the contribution from more distant clusters becomes progressively more diluted by the WMAP beam. We can, however, at present not rule out that these more distant clusters simply contribute less to the overall motion.

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arXiv2009

A measurement of large-scale peculiar velocities of clusters of galaxies: technical details

This paper presents detailed analysis of large-scale peculiar motions derived from a sample of ~ 700 X-ray clusters and cosmic microwave background (CMB) data obtained with WMAP. We use the kinematic Sunyaev-Zeldovich (KSZ) effect combining it into a cumulative statistic which preserves the bulk motion component with the noise integrated down. Such statistic is the dipole of CMB temperature fluctuations evaluated over the pixels of the cluster catalog (Kashlinsky & Atrio-Barandela 2000). To remove the cosmological CMB fluctuations the maps are Wiener-filtered in each of the eight WMAP channels (Q, V, W) which have negligible foreground component. Our findings are as follows: The thermal SZ (TSZ) component of the clusters is described well by the Navarro-Frenk-White profile expected if the hot gas traces the dark matter in the cluster potential wells. Such gas has X-ray temperature decreasing rapidly towards the cluster outskirts, which we demonstrate results in the decrease of the TSZ component as the aperture is increased to encompass the cluster outskirts. We then detect a statistically significant dipole in the CMB pixels at cluster positions. Arising exclusively at the cluster pixels this dipole cannot originate from the foreground or instrument noise emissions and must be produced by the CMB photons which interacted with the hot intracluster gas via the SZ effect. The dipole remains as the monopole component, due to the TSZ effect, vanishes within the small statistical noise out to the maximal aperture where we still detect the TSZ component. We demonstrate with simulations that the mask and cross-talk effects are small for our catalog and contribute negligibly to the measurements. The measured dipole thus arises from the KSZ effect produced by the coherent large scale bulk flow motion.

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arXiv2008

A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications

Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3-year WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least > 300 h^{-1} Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.

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arXiv2008

Measurement of the electron-pressure profile of galaxy clusters in Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data

Using WMAP 3-year data at the locations of close to $\sim 700$ X-ray selected clusters we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ) effect at the 15$σ$ level, the highest statistical significance reported so far. Owing to the large size of our cluster sample, we are able to detect the corresponding CMB distortions out to large cluster-centric radii. The region over which the TSZ signal is detected is, on average, four times larger in radius than the X-ray emitting region, extending to $\sim 3h_{70}^{-1}$Mpc. We show that an isothermal $β$ model does not fit the electron pressure at large radii; instead, the baryon profile is consistent with the Navarro-Frenk-White profile, expected for dark matter in the concordance $Λ$CDM model. The X-ray temperature at the virial radius of the clusters falls by a factor $\sim 3-4$ from the central value, depending on the cluster concentration parameter. Our results suggest that cluster dynamics at large radii is dominated by dark matter and is well described by Newtonian gravity.

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arXiv2008

Kinematic Sunyaev-Zeldovich Cosmic Microwave Background Temperature Anisotropies Generated by Gas in Cosmic Structures

If the gas in filaments and halos shares the same velocity field than the luminous matter, it will generate measurable temperature anisotropies due to the Kinematic Sunyaev-Zeldovich effect. We compute the distribution function of the KSZ signal produced by a typical filament and show it is highly non-gaussian. The combined contribution of the Thermal and Kinematic SZ effects of a filament of size $L\simeq 5$Mpc and electron density $n_e\simeq 10^3m^{-3}$ could explain the cold spots of $δ\sim -200μ$K on scales of 30' found in the Corona Borealis Supercluster by the VSA experiment. PLANCK, with its large resolution and frequency coverage, could provide the first evidence of the existence of filaments in this region. The KSZ contribution of the network of filaments and halo structures to the radiation power spectrum peaks around $l\sim 400$, a scale very different from that of clusters of galaxies, with a maximum amplitude $l(l+1)C_l/2π\sim 10-25 (μK)^2$, depending on model parameters, i.e., $σ_8$ and the Jeans length. About 80% of the signal comes from filaments with redshift $z\le 0.1$. Adding this component to the intrinsic Cosmic Microwave Background temperature anisotropies of the concordance model improves the fit to WMAP 3yr data by $Δχ^2\simeq 1$. The improvement is not statistically significant but a more systematic study could demonstrate that gas could significantly contribute to the anisotropies measured by WMAP.

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arXiv2006

Matter density perturbations in interacting quintessence models

Models with dark energy decaying into dark matter have been proposed to solve the coincidence problem in cosmology. We study the effect of such coupling in the matter power spectrum. Due to the interaction, the growth of matter density perturbations during the radiation dominated regime is slower compared to non-interacting models with the same ratio of dark matter to dark energy today. This effect introduces a damping on the power spectrum at small scales proportional to the strength of the interaction and similar to the effect generated by ultrarelativistic neutrinos. The interaction also shifts matter--radiation equality to larger scales. We compare the matter power spectrum of interacting quintessence models with the measurments of 2dFGRS. We particularize our study to models that during radiation domination have a constant dark matter to dark energy ratio.

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arXiv2006

The Contribution of the Intergalactic Medium to Cosmic Microwave Background Anisotropies

We compute the power spectrum of the Cosmic Microwave Background temperature anisotropies generated by the Intergalactic Medium. To estimate the electron pressure along the line of sight and its contribution to the Sunyaev-Zeldovich component of the CMB anisotropies, we assume the non-linear baryonic density contrast is well described by a log-normal distribution. For model parameters in agreement with observations and for an experiment operating in the Rayleigh-Jeans regime, the largest IGM contribution is expected at scales corresponding to multipole numbers of about 2000. The amplitude is rather uncertain and could be as large as 100-200 [mikroK]^2, comparable to the contribution of galaxy clusters. The actual value is strongly dependent on the gas polytropic index and the amplitude of the matter power spectrum sigma_8. At all redshifts, the largest contribution comes from scales very close to the comoving baryon Jeans length. This scale is not yet resolved in numerical simulations that follow the evolution of gas on cosmological scales. The anisotropy generated by the Intergalactic Medium could make compatible the excess of power measured by Cosmic Background Imager (CBI) on scales of l > 2000 with sigma_8=0.9. Taking the CBI result as an upper limit, the polytropic index can be constrained to < 1.5 at 2-sigma level at redshifts z ~ 0.1-0.4. With its large frequency coverage, the PLANCK satellite will be able to measure the secondary anisotropies coming from hot gas. Cluster and Intergalactic Medium contributions could be separated by cross correlating galaxy/cluster catalogs with CMB maps. This measurement will determine the state of the gas at low and intermediate redshifts.

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arXiv2004

The Effect of Hot Gas in WMAP's First Year Data

By cross-correlating templates constructed from the 2 Micron All Sky Survey (2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local Universe. Assuming that galaxies trace the distribution of hot gas, we select regions on the sky with the largest projected density of galaxies. Under conservative assumptions on the amplitude of foreground residuals, we find a temperature decrement of -35 $\pm$ 7 $μ$K ($\sim 5σ$ detection level, the highest reported so far) in the $\sim$ 26 square degrees of the sky containing the largest number of galaxies per solid angle. We show that most of the reported signal is caused by known galaxy clusters which, when convolved with the average beam of the WMAP W band channel, subtend a typical angular size of 20--30 arcmins. Finally, after removing from our analyses all pixels associated with known optical and X-ray galaxy clusters, we still find a tSZ decrement of -96 $\pm$ 37 $μ$K in pixels subtending about $\sim$ 0.8 square degrees on the sky. Most of this signal is coming from five different cluster candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA (CIZA) catalogue. We found no evidence that structures less bound than clusters contribute to the tSZ signal present in the WMAP data.

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arXiv2003

Using peak distribution of the cosmic microwave background for MAP and Planck data analysis: formalism and simulations

We implement and further refine the recently proposed method (Kashlinsky, Hernández-Monteagudo & Atrio-Barandela, 2001 - KHA) for a time efficient extraction of the power spectrum from future cosmic microwave background (CMB) maps. The method is based on the clustering properties of peaks and troughs of the Gaussian CMB sky. The procedure takes only ${1/2}[f(ν)]^2N^2$ steps where $f(ν)$ is the fraction of pixels with $|δT|\geqν$ standard deviations in the map of $N$ pixels. We use the new statistic introduced in KHA, $ξ_ν$, which characterizes spatial clustering of the CMB sky peaks of progressively increasing thresholds. The tiny fraction of the remaining pixels (peaks and troughs) contains the required information on the CMB power spectrum of the entire map. The threshold $ν$ is the only parameter that determines the accuracy of the final spectrum. We performed detailed numerical simulations for parameters of the two-year WMAP and Planck CMB sky data including cosmological signal, inhomogeneous noise and foreground residuals. In all cases we find that the method can recover the power spectrum out to the Nyquist scale of the experiment channel. We discuss how the error bars scale with $ν$ allowing to decide between accuracy and speed. The method can determine with significant accuracy the CMB power spectrum from the upcoming CMB maps in only $\sim(10^{-5}-10^{-3})\times N^2$ operations.

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arXiv2001

Observational Matter Power Spectrum and the Height of the Second Acoustic Peak

We show that the amplitude of the second acoustic peak in the newly released BOOMERANG-98 and MAXIMA-I data is compatible with the standard primordial nucleosynthesis and with the locally broken-scale-invariant matter power spectrum suggested by recent measurements of the power spectrum in the range $20 - 200$ Mpc. If the slope of matter density perturbations on large scales is $n \approx 1$, the Hubble constant is $0.5< h < 0.75$, and r.m.s. mass fluctuations at 8 Mpc are $0.65 \le σ_8 \le 0.75$, then for a Universe approximately 14 Gyr old our best fit within the nucleosynthesis bound $Ω_Bh^2= 0.019 \pm 0.0024$ requires $0.3 \le Ω_m \le 0.5$. Cluster abundances further constraint the matter density to be $Ω_m \approx 0.3$. The CMB data alone are not able to determine the detailed form of the matter power spectrum in the range $0.03<k<0.06$ \hmpc where deviations from the scale-invariant spectrum are expected to be most significant, but they do not contradict the existence of the previously claimed peak at $k\sim 0.05$ \hmpc, and a depression at $k\sim 0.035$ \hmpc.

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arXiv2000

Measuring cosmological bulk flows via the kinematic Sunyaev-Zeldovich effect in the upcoming cosmic microwave background maps

We propose a new method to measure the possible large-scale bulk flows in the Universe from the cosmic microwave background (CMB) maps from the upcoming missions, MAP and Planck. This can be done by studying the statistical properties of the CMB temperature field at many X-ray cluster positions. At each cluster position, the CMB temperature fluctuation will be a combination of the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological fluctuations and the instrument noise term. When averaged over many such clusters the last three will integrate down, whereas the first one will be dominated by a possible bulk flow component. In particular, we propose to use all-sky X-ray cluster catalogs that should (or could) be available soon from X-ray satellites, and then to evaluate the dipole component of the CMB field at the cluster positions. We show that for the MAP and Planck mission parameters the dominant contributions to the dipole will be from the terms due to the SZ kinematic effect produced by the bulk flow (the signal we seek) and the instrument noise (the noise in our signal). Computing then the expected signal-to-noise ratio for such measurement, we get that at the 95 % confidence level the bulk flows on scales >100h^{-1} Mpc can be probed down to the amplitude of $< 200$ km/sec with the MAP data and down to only 30 km/sec with the Planck mission.

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arXiv2000

Limits on Hot Intracluster Gas Contributions to the Tenerife Temperature Anisotropy Map

We limit the contribution of the hot intracluster gas, by means of the Sunyaev-Zel'dovich effect, to the temperature anisotropies measured by the Tenerife experiment. The data is cross-correlated with maps generated from the ACO cluster catalogue, the ROSAT PSPC catalogue of clusters of galaxies, a catalogue of superclusters and the HEAO 1 A-1 map of X-ray sources. There is no evidence of contamination by such sources at an rms level of $\sim 8μ$K at 99% confidence level at $5^o$ angular resolution. We place an upper limit on the mean Comptonization parameter of $ y \le 1.5\times 10^{-6}$ at the same level of confidence. These limits are slightly more restrictive than those previously found by a similar analysis on the COBE/DMR data and indicate that most of the signal measured by Tenerife is cosmological.

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arXiv1999

On the Number Density of Sunyaev-Zel'dovich Clusters of Galaxies

If the mean properties of clusters of galaxies are well described by the entropy-driven model, the distortion induced by the cluster population on the blackbody spectrum of the Cosmic Microwave Background radiation is proportional to the total amount of intracluster gas while temperature anisotropies are dominated by the contribution of clusters of about 10^{14} solar masses. This result depends marginally on cluster parameters and it can be used to estimate the number density of clusters with enough hot gas to produce a detectable Sunyaev-Zel'dovich effect. Comparing different cosmological models, the relation depends mainly on the density parameter Omega_m. If the number density of clusters could be estimated by a different method, then this dependence could be used to constrain Omega_m.

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arXiv1998

Steps toward the power spectrum of matter. I.The mean spectrum of galaxies

We calculate the mean power spectrum of galaxies using published power spectra of galaxies and clusters of galaxies. On small scales we use the power spectrum derived from the 2-dimensional distribution of APM galaxies, on large scales we use power spectra derived from 3-dimensional data for galaxy and cluster samples. Spectra are reduced to real space and to the amplitude of the power spectrum of APM galaxies. Available data indicate the presence of two different populations in the nearby Universe. Clusters of galaxies sample a relatively large region in the Universe where rich, medium and poor superclusters are well represented. Their mean power spectrum has a spike on scale 120 h^{-1}Mpc, followed by an approximate power-law spectrum of index n = -1.9 towards small scales. The power spectrum found from LCRS and IRAS 1.2 Jy surveys is flatter around the maximum, which may represent regions of the Universe with medium-rich and poor superclusters.

astro-ph↗

arXiv1998

Steps toward the power spectrum of matter. II. The biasing correction with sigma_8 normalization

A new method to determine the bias parameter of galaxies relative to matter is suggested. The method is based on the assumption that gravity is the dominating force which determines the formation of the structure in the Universe. Due to gravitational instability the galaxy formation is a threshold process: in low-density environments galaxies do not form and matter remains in primordial form. We investigate the influence of the presence of void and clustered populations to the power spectrum of matter and galaxies. The power spectrum of galaxies is similar to the power spectrum of matter; the fraction of total matter in the clustered population determines the difference between amplitudes of fluctuations of matter and galaxies, i.e. the bias factor. To determine the fraction of matter in voids and clustered population we perform numerical simulations. The fraction of matter in galaxies at the present epoch is found using a calibration through the sigma_8 parameter.

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arXiv1998

Steps toward the power spectrum of matter. III. The primordial spectrum

Observed power spectrum of matter found in Papers I and II is compared with analytical power spectra. Spatially flat cold and mixed dark matter models with cosmological constant and open models are considered. The primordial power spectrum of matter is determined using the power spectrum of matter and the transfer functions of analytical models. The primordial power spectrum has a break in amplitude. We conclude that a scale-free primordial power spectrum is excluded if presently available data on the distribution of clusters and galaxies represent the true mass distribution of the Universe.

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