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M. Douspis

Publications and source records attributed to M. Douspis.

At least 289 records · Page 16Linked to original sources
arXiv2011

Planck early results: first assessment of the High Frequency Instrument in-flight performance

The Planck High Frequency Instrument (HFI) is designed to measure the temperature and polarization anisotropies of the Cosmic Microwave Background and galactic foregrounds in six wide bands centered at 100, 143, 217, 353, 545 and 857 GHz at an angular resolution of 10' (100 GHz), 7' (143 GHz), and 5' (217 GHz and higher). HFI has been operating flawlessly since launch on 14 May 2009. The bolometers cooled to 100 mK as planned. The settings of the readout electronics, such as the bolometer bias current, that optimize HFI's noise performance on orbit are nearly the same as the ones chosen during ground testing. Observations of Mars, Jupiter, and Saturn verified both the optical system and the time response of the detection chains. The optical beams are close to predictions from physical optics modeling. The time response of the detection chains is close to pre-launch measurements. The detectors suffer from an unexpected high flux of cosmic rays related to low solar activity. Due to the redundancy of Planck's observations strategy, the removal of a few percent of data contaminated by glitches does not affect significantly the sensitivity. The cosmic rays heat up significantly the bolometer plate and the modulation on periods of days to months of the heat load creates a common drift of all bolometer signals which do not affect the scientific capabilities. Only the high energy cosmic rays showers induce inhomogeneous heating which is a probable source of low frequency noise.

astro-ph.IM↗
arXiv2011

Planck early results: Cluster Sunyaev-Zeldovich optical scaling relations

We present the Sunyaev-Zeldovich (SZ) signal-to-richness scaling relation (Y500-N200) for the MaxBCG cluster catalogue. Employing a multi-frequency matched filter on the Planck sky maps, we measure the SZ signal for each cluster by adapting the filter according to weak-lensing calibrated mass-richness relations (N200-M500). We bin our individual measurements and detect the SZ signal down to the lowest richness systems (N200=10) with high significance, achieving a detection of the SZ signal in systems with mass as low as M500~5e13 Msolar. The observed Y500-N200 relation is well modeled by a power law over the full richness range. It has a lower normalisation at given N200 than predicted based on X-ray models and published mass-richness relations. An X-ray subsample, however, does conform to the predicted scaling, and model predictions do reproduce the relation between our measured bin-average SZ signal and measured bin-average X-ray luminosities. At fixed richness, we find an intrinsic dispersion in the Y500-N200 relation of 60% rising to of order 100% at low richness. Thanks to its all-sky coverage, Planck provides observations for more than 13,000 MaxBCG clusters and an unprecedented SZ/optical data set, extending the list of known cluster scaling laws to include SZ-optical properties. The data set offers essential clues for models of galaxy formation. Moreover, the lower normalisation of the SZ-mass relation implied by the observed SZ-richness scaling has important consequences for cluster physics and cosmological studies with SZ clusters.

astro-ph.CO↗
arXiv2010

The ISW-tSZ cross correlation: ISW extraction out of pure CMB data

If Dark Energy introduces an acceleration in the universal expansion then large scale gravitational potential wells should be shrinking, causing a blueshift in the CMB photons that cross such structures (Integrated Sachs-Wolfe effect, [ISW]). Galaxy clusters are known to probe those potential wells. In these objects, CMB photons also experience inverse Compton scattering off the hot electrons of the intra-cluster medium, and this results in a distortion with a characteristic spectral signature of the CMB spectrum (the so-called thermal Sunyaev-Zel'dovich effect, [tSZ]). Since both the ISW and the tSZ effects take place in the same potential wells, they must be spatially correlated. We present how this cross ISW-tSZ signal can be detected in a CMB-data contained way by using the frequency dependence of the tSZ effect in multi frequency CMB experiments like {\it Planck}, {\em without} requiring the use of external large scale structure tracers data. We find that by masking low redshift clusters, the shot noise level decreases significantly, boosting the signal to noise ratio of the ISW--tSZ cross correlation. We also find that galactic and extragalactic dust residuals must be kept at or below the level of ~0.04 muK^2 at l=10, a limit that is a factor of a few below {\it Planck}'s expectations for foreground subtraction. If this is achieved, CMB observations of the ISW-tSZ cross correlation should also provide an independent probe for the existence of Dark Energy and the amplitude of density perturbations.

astro-ph.CO↗
arXiv2009

Sunyaev-Zel'dovich contribution in CMB analysis

The Sunyaev-Zel'dovich (SZ) effect has long been identified as one of the most important secondary effects of the Cosmic Microwave Background (CMB). On the one hand, it is a potentially very powerful cosmological probe providing us with additional constraints and on the other hand it represents the major source of secondary fluctuations at small angular scales (l > 1000). We investigate the effects of the SZ modelling in the determination of the cosmological parameters. We explore the consequences of the SZ power spectrum computation by comparing three increasingly complex modelling, from a fixed template with an amplitude factor to a calculation including the full cosmological parameter dependency. We also examine the dependency of the cosmological parameter estimation on the intra-cluster gas description used to calculate the SZ spectrum. We show that methods assuming an SZ template bias the cosmological parameters (by up to 2 sigmas on sigma_8) when the cosmology used in the template deviates from the reference one. A joint CMB-SZ analysis with a full cosmological dependency of the SZ spectrum does not suffer from such biases and moreover improves the confidence intervals of sigma_8 and Omega_{dm}h^2 (2.5 and 2 times respectively) with respect to a pure CMB analysis. However, the latter method is quite sensitive to the intra-cluster gas parameters and hence requires extra information on the clusters to alleviate the induced biases.

astro-ph.CO↗
arXiv2006

Archeops In-flight Performance, Data Processing and Map Making

Archeops is a balloon--borne experiment widely inspired by the Planck satellite and by its High Frequency Instrument (HFI). It is mainly dedicated to measure the Cosmic Microwave Background (CMB) temperature anisotropies at high angular resolution (about 12 arcminutes) over a large fraction of the sky (around 30 %) in the millimetre and submillimetre range at 143, 217, 353 and 545 GHz. Further, the Archeops 353 GHz channel consists of three pairs of polarized sensitive bolometers designed to detect the polarized diffuse emission of Galactic dust. We present in this paper the update of the instrumental setup as well as the inflight performance for the last Archeops flight campaign in February 2002 from Kiruna (Sweden). We also describe the processing and analysis of the Archeops time ordered data for that campaign which lead to the measurement of the CMB anisotropies power spectrum in the multipole range l=10-700 (Benoit et al. 2003a, Tristram et al. 2005) and to the first measurement of the dust polarized emission at large angular scales and its polarized. We present maps of 30 % of the sky of the Galactic emission, including the Galactic plane, in the four Archeops channels at 143, 217, 353 and 545 GHz and maps of the CMB anisotropies at 143 and 217 GHz. These are the firstever available sub--degree resolution maps in the millimetre and submillimetre range of the large angular-scales Galactic dust diffuse emission and CMB temperature anisotropies respectively.

astro-ph↗
arXiv2005

The CMB temperature power spectrum from an improved analysis of the Archeops data

We present improved results on the measurement of the angular power spectrum of the Cosmic Microwave Background (CMB) temperature anisotropies using the data from the last Archeops flight. This refined analysis is obtained by using the 6 most sensitive photometric pixels in the CMB bands centered at 143 and 217 GHz and 20% of the sky, mostly clear of foregrounds. Using two different cross-correlation methods, we obtain very similar results for the angular power spectrum. Consistency checks are performed to test the robustness of these results paying particular attention to the foreground contamination level which remains well below the statistical uncertainties. The multipole range from l=10 to l=700 is covered with 25 bins, confirming strong evidence for a plateau at large angular scales (the Sachs-Wolfe plateau) followed by two acoustic peaks centered around l=220 and l=550 respectively. These data provide an independent confirmation, obtained at different frequencies, of the WMAP first year results.

astro-ph↗
arXiv2005

Temperature and polarization angular power spectra of Galactic dust radiation at 353 GHz as measured by Archeops

We present the first measurement of temperature and polarization angular power spectra of the diffuse emission of Galactic dust at 353 GHz as seen by Archeops on 20% of the sky. The temperature angular power spectrum is compatible with that provided by the extrapolation to 353 GHz of IRAS and DIRBE maps using \cite{fds} model number 8. For Galactic latitudes $|b| \geq 5$ deg we report a 4 sigma detection of large scale ($3\leq \ell \leq 8$) temperature-polarization cross-correlation $(\ell+1)C_\ell^{TE}/2π= 76\pm 21 μ\rm{K_{RJ}}^2$ and set upper limits to the $E$ and $B$ modes at $11 μ\rm{K_{RJ}}^2$. For Galactic latitudes $|b| \geq 10$ deg, on the same angular scales, we report a 2 sigma detection of temperature-polarization cross-correlation $(\ell+1)C_\ell^{TE}/2π= 24\pm 13 μ\rm{K_{RJ}}^2$. These results are then extrapolated to 100 GHz to estimate the contamination in CMB measurements by polarized diffuse Galactic dust emission. The $TE$ signal is then $1.7\pm0.5$ and $0.5\pm0.3 μ\rm{K^2_{CMB}}$ for $|b| \geq 5$ and 10 deg. respectively. The upper limit on $E$ and $B$ becomes $0.2 μ\rm{K^2_{CMB}} (2σ)$. If polarized dust emission at higher Galactic latitude cuts is similar to the one we report here, then dust polarized radiation will be a major foreground for determining the polarization power spectra of the CMB at high frequencies above 100 GHz.

astro-ph↗
arXiv2003

First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops

We present the first determination of the Galactic polarized emission at 353 GHz by Archeops. The data were taken during the Arctic night of February 7, 2002 after the balloon--borne instrument was launched by CNES from the Swedish Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz bolometers mounted in three polarization sensitive pairs that were used for Galactic foreground studies. We present maps of the I, Q, U Stokes parameters over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns). They show a significant Galactic large scale polarized emission coherent on the longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization at the level of 4-5%, in agreement with expectations from starlight polarization measurements. Some regions in the Galactic plane (Gem OB1, Cassiopeia) show an even stronger degree of polarization in the range 10-20%. Those findings provide strong evidence for a powerful grain alignment mechanism throughout the interstellar medium and a coherent magnetic field coplanar to the Galactic plane. This magnetic field pervades even some dense clouds. Extrapolated to high Galactic latitude, these results indicate that interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB polarization measurement.

astro-ph↗
arXiv2003

Goodness--of--fit Statistics and CMB Data Sets

Application of a Goodness--of--fit (GOF) statistic is an essential element of parameter estimation. We discuss the computation of GOF when estimating parameters from anisotropy measurements of the cosmic microwave background (CMB), and we propose two GOF statistics to be used when employing approximate band--power likelihood functions. They are based on an approximate form for the distribution of band--power estimators that requires only minimal experimental information to construct. Monte Carlo simulations of CMB experiments show that the proposed form describes the true distributions quite well. We apply these GOF statistics to current CMB anisotropy data and discuss the results.

astro-ph↗
arXiv2003

Cosmological constraints in Lambda-CDM and Quintessence paradigms with Archeops

We review the cosmological constraints put by the current CMB experiment including the recent ARCHEOPS data, in the framework of Lambda-CDM and quintessence paradigm. We show that well chosen combinations of constraints from different cosmological observations lead to precise measurements of cosmological parameters. The Universe seems flat with a 70 percents contribution of dark energy with an equation of state very close to those of the vacuum.

astro-ph↗
arXiv2003

Cosmological constraints from Archeops

We analyze the cosmological constraints that Archeops places on adiabatic cold dark matter models with passive power-law initial fluctuations. Because its angular power spectrum has small bins in l and large l coverage down to COBE scales, Archeops provides a precise determination of the first acoustic peak in terms of position at multipole l_peak=220 +- 6, height and width. An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe, Omega(b)h^2 = 0.022 (+0.003,-0.004), compatible with Big-Bang nucleosynthesis and with a similar accuracy. Using cosmological priors obtainedfrom recent non-CMB data leads to yet tighter constraints on the total density, e.g. Omega(tot)=1.00 (+0.03,-0.02) using the HST determination of the Hubble constant. An excellent absolute calibration consistency is found between Archeops and other CMB experiments, as well as with the previously quoted best fit model.The spectral index n is measured to be 1.04 (+0.10,-0.12) when the optical depth to reionization, tau, is allowed to vary as a free parameter, and 0.96 (+0.03,-0.04) when tau is fixed to zero, both in good agreement with inflation.

astro-ph↗
arXiv2003

The Cosmic Microwave Background Anisotropy Power Spectrum measured by Archeops

We present a determination by the Archeops experiment of the angular power spectrum of the cosmic microwave background anisotropy in 16 bins over the multipole range l=15-350. Archeops was conceived as a precursor of the Planck HFI instrument by using the same optical design and the same technology for the detectors and their cooling. Archeops is a balloon-borne instrument consisting of a 1.5 m aperture diameter telescope and an array of 21 photometers maintained at ~100 mK that are operating in 4 frequency bands centered at 143, 217, 353 and 545 GHz. The data were taken during the Arctic night of February 7, 2002 after the instrument was launched by CNES from Esrange base (Sweden). The entire data cover ~ 30% of the sky.This first analysis was obtained with a small subset of the dataset using the most sensitive photometer in each CMB band (143 and 217 GHz) and 12.6% of the sky at galactic latitudes above 30 degrees where the foreground contamination is measured to be negligible. The large sky coverage and medium resolution (better than 15 arcminutes) provide for the first time a high signal-to-noise ratio determination of the power spectrum over angular scales that include both the first acoustic peak and scales probed by COBE/DMR. With a binning of Delta(l)=7 to 25 the error bars are dominated by sample variance for l below 200. A companion paper details the cosmological implications.

astro-ph↗
arXiv2002

Cosmological parameters estimation in the Quintessence Paradigm

We present cosmological parameter constraints on flat cosmologies dominated by dark energy using various cosmological data including the recent Archeops angular power spectrum measurements. A likelihood analysis of the existing Cosmic Microwave Background data shows that the presence of dark energy is not requested, in the absence of further prior. This comes from the fact that there exist degeneracies among the various cosmological parameters constrained by the Cosmic Microwave Background. We found that there is a degeneracy in a combination of the Hubble parameter H_0 and of the dark energy equation of state parameter w_Q, but that w_Q is not correlated with the primordial index n of scalar fluctuations and the baryon content Omega_b h^2. Preferred primordial index is n = 0.95 \pm 0.05 (68%) and baryon content Omega_b h^2 = 0.021 \pm 0.003. Adding constraint on the amplitude of matter fluctuations on small scales, sigma_8, obtained from clusters abundance or weak lensing data may allow to break the degenaracies, although present-day systematics uncertainties do not allow firm conclusions yet. The further addition of the Hubble Space Telescope measurements of the local distance scale and of the high redshift supernovae data allows to obtain tight constraints. When these constraints are combined together we find that the amount of dark energy is 0.7^{+0.10}_{-0.07} (95% C.L.) and that its equation of state is very close to those of the vacuum: w_Q < -0.75 (> 95% C.L.). In no case do we find that quintessence is prefered over the classical cosmological constant, although robust data on sigma_8 might rapidly bring light on this important issue.

astro-ph↗
arXiv2001

Cosmological Parameter Estimation from CMB and X-ray clusters

We present the results of a combined analysis of cosmic microwave background (CMB) and X-ray galaxy clusters baryon fraction to deduce constraints over 6 in flationnary cosmological parameters. Such a combination is necessary for breaki ng degeneracies inherent to the CMB.

astro-ph↗
arXiv2001

The baryon fraction in X-Rays galaxy clusters revisited

One of the most direct way to constrain the matter density of the universe $Ω_M$ is to measure the baryon content in X-Rays clusters of galaxies. Typical value of the mean gas mass fraction is $\fg \sim 0.15h^{-3/2}$ which leads to $\omM <0.4$. In this talk I will discuss the issue of the gas fraction radial distribution inside a cluster and foccus on the apparent discrepancy between the theoretical shape predicted by numerical simulations and the observations. I will show that a significant part of this discrepancy is due to several systematics in both the gas mass and total mass determinations. Revising the gas as well as the binding masses removes such a discrepancy and results in a lower baryon mass fraction of $\fb(r_{500}) \sim 10 %$ (Sadat & Blanchard 2001). Finally, I will discuss the cosmological constraints we obtain when we combine the revised baryon fraction with primordial fluctuations.

astro-ph↗
arXiv2001

Cosmology from Cosmic Microwave Background and Galaxy Clusters

We present the results of analysis of constraints on cosmological parameters from cosmic microwave background (CMB) alone and in combination with galaxy cluster baryon fraction assuming inflation--generated adiabatic scalar fluctuations. The CMB constraints are obtained using our likelihood approximation method (Bartlett et al., 2000, Douspis et al., 2001). In the present analysis we use the new data coming from MAXIMA and BOOMERanG balloon borne experiments, the first results of the DASI interferometer together with the COBE/DMR data. The quality of these independent data sets implies that the $C_\ell$ are rather well known, and allow reliable constraints. We found that the constraints in the $Ω-H_0$ plane are very tightened, favouring a flat Universe, that the index of the primordial fluctuations is very close to one, that the primordial baryon density is now in good agreement with primordial nucleosynthesis. Nevertheless degeneracies between several parameters still exist, and for instance the constraint on the cosmological constant or the Hubble constant are very weak, preferred values being low. A way to break these degeneracies is to ``cross-constrain'' the parameters by combining with constraints from other independent data. We use the baryon fraction determination from X-ray clusters of galaxies as an additional constraint and show that the combined analysis leads to strong constraints on all cosmological parameters. Using a high baryon fraction ($\sim 15%$ for $h = 0.5$) we found a rather low Hubble constant, values around 80 km/s/Mpc being ruled out. Using a recent and low baryon fraction estimation ($\sim 10%$ for $h = 0.5$) we found a preferred model with a low Hubble constant and a high density content ($Ω_m$), an Einstein--de Sitter model being only weakly ruled out.

astro-ph↗
arXiv2001

Bias in Matter Power Spectra ?

We review the constraints given by the linear matter power spectra data on cosmological and bias parameters, comparing the data from the PSCz survey (Hamilton et al., 2000) and from the matter power spectrum infered by the study of Lyman alpha spectra at z=2.72 (Croft et al., 2000). We consider flat--$Λ$ cosmologies, allowing $Λ$, $H_0$ and $n$ to vary, and we also let the two ratio factors $r_{pscz}$ and $r_{lyman}$ ($r^2_i = \frac{P_{i}(k)}{P_{CMB}(k)}$) vary independently. Using a simple $χ^2$ minimisation technique, we find confidence intervals on our parameters for each dataset and for a combined analysis. Letting the 5 parameters vary freely gives almost no constraints on cosmology, but requirement of a universal ratio for both datasets implies unacceptably low values of $H_0$ and $Λ$. Adding some reasonable priors on the cosmological parameters demonstrates that the power derived by the PSCz survey is higher by a factor $\sim 1.75$ compared to the power from the Lyman $α$ forest survey.

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