arXiv subjects

Paolo Serra

Publications and source records attributed to Paolo Serra.

At least 127 records · Page 7Linked to original sources

arXiv2010

A Constraint On the Integrated Mass Power Spectrum out to z = 1100 from Lensing of the Cosmic Microwave Background

The temperature fluctuations and polarization of the Cosmic Microwave Background (CMB) are now a well-known probe of the Universe at an infant age of 400,000 years. During the transit to us from the surface of last scattering, the CMB photons are expected to undergo modifications induced by the intervening large-scale structure. Among the expected secondary effects is the weak gravitational lensing of the CMB by the foreground dark matter distribution. We derive a quadratic estimator that uses the non-Gaussianities generated by the lensing effect at the four-point function level to extract the power spectrum of lensing potential fluctuations integrated out to z ~ 1100 with peak contributions from potential fluctuations at z of 2 to 3. Using WMAP 7-year temperature maps, we report the first direct constraints of this lensing potential power spectrum and find that it has an amplitude of A_L = 0.96 +/- 0.60, 1.06 +/- 0.69 and 0.97 +/- 0.47 using the W, V and W+V bands, respectively.

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arXiv2010

The Atlas3D project -- I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria

The Atlas3D project is a multi-wavelength survey combined with a theoretical modeling effort. The observations span from the radio to the millimeter and optical, and provide multi-colour imaging, two-dimensional kinematics of the atomic (HI), molecular (CO) and ionized gas (Hbeta, [OIII] and [NI]), together with the kinematics and population of the stars (Hbeta, Fe5015 and Mgb), for a carefully selected, volume-limited (1.16*10^5 Mpc^3) sample of 260 early-type (elliptical E and lenticular S0) galaxies (ETGs). The models include semi-analytic, N-body binary mergers and cosmological simulations of galaxy formation. Here we present the science goals for the project and introduce the galaxy sample and the selection criteria. The sample consists of nearby (D<42 Mpc) morphologically-selected ETGs extracted from a parent sample of 871 galaxies (8% E, 22% S0 and 70% spirals) brighter than M_K<-21.5 mag (stellar mass M_Star>6*10^9 M_Sun). We analyze possible selection biases and we conclude that the parent sample is essentially complete and statistically representative of the nearby galaxy population. We present the size-luminosity relation for the spirals and ETGs and show that the ETGs in the Atlas3D sample define a tight red sequence in a colour-magnitude diagram, with few objects in the transition from the blue cloud. We describe the strategy of the SAURON integral-field observations and the extraction of the stellar kinematics with the pPXF method. We give an overview of the characteristics of the other main datasets already available for our sample and of the ongoing modelling projects.

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arXiv2010

The Westerbork Hydrogen Accretion in Local Galaxies (HALOGAS) Survey I. Survey Description and Pilot Observations

We introduce a new, very deep neutral hydrogen (HI) survey being performed with the Westerbork Synthesis Radio Telescope (WSRT). The Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey is producing an archive of some of the most sensitive HI observations available, on the angular scales which are most useful for studying faint, diffuse gas in and around nearby galaxies. The survey data are being used to perform careful modeling of the galaxies, characterizing their gas content, morphology, and kinematics, with the primary goal of revealing the global characteristics of cold gas accretion onto spiral galaxies in the local Universe. In this paper, we describe the survey sample selection, the data acquisition, reduction, and analysis, and present the data products obtained during our pilot program, which consists of UGC 2082, NGC 672, NGC 925, and NGC 4565. The observations reveal a first glimpse of the picture that the full HALOGAS project aims to illuminate: the properties of accreting HI in different types of spirals, and across a range of galactic environments. None of the pilot survey galaxies hosts an HI halo of the scale of NGC 891, but all show varying indications of halo gas features. We compare the properties of detected features in the pilot survey galaxies with their global characteristics, and discuss similarities and differences with NGC 891 and NGC 2403.

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arXiv2010

Constraints on primordial non-Gaussianity from WMAP7 and Luminous Red Galaxies power spectrum and forecast for future surveys

We place new constraints on the primordial local non-Gaussianity parameter f_NL using recent Cosmic Microwave Background anisotropy and galaxy clustering data. We model the galaxy power spectrum according to the halo model, accounting for a scale dependent bias correction proportional to f_NL/k^2. We first constrain f_NL in a full 13 parameters analysis that includes 5 parameters of the halo model and 7 cosmological parameters. Using the WMAP7 CMB data and the SDSS DR4 galaxy power spectrum, we find f_NL=171\pm+140 at 68% C.L. and -69<f_NL<+492 at 95% C.L.. We discuss the degeneracies between f_NL and other cosmological parameters. Including SN-Ia data and priors on H_0 from Hubble Space Telescope observations we find a stronger bound: -35<f_NL<+479 at 95% C.L.. We also fit the more recent SDSS DR7 halo power spectrum data finding, for a Λ-CDM+f_NL model, f_NL=-93\pm128 at 68% C.L. and -327<f_{NL}<+177 at 95% C.L.. We finally forecast the constraints on f_NL from future surveys as EUCLID and from CMB missions as Planck showing that their combined analysis could detect f_NL\sim 5.

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arXiv2010

Impact of general reionization scenarios on extraction of inflationary parameters

Determination of whether the Harrison--Zel'dovich spectrum for primordial scalar perturbations is consistent with observations is sensitive to assumptions about the reionization scenario. In light of this result, we revisit constraints on inflationary models using more general reionization scenarios. While the bounds on the tensor-to-scalar ratio are largely unmodified, when different reionization schemes are addressed, hybrid models are back into the inflationary game. In the general reionization picture, we reconstruct both the shape and amplitude of the inflaton potential. We find a broader spectrum of potential shapes when relaxing the simple reionization restriction. An upper limit of $10^{16}$ GeV to the amplitude of the potential is found, regardless of the assumptions on the reionization history.

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arXiv2010

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs.

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arXiv2010

The Impact of Secondary non-Gaussianities in the CMB on Cosmological Parameter Estimation

We consider corrections to the underlying cosmology due to secondary contributions from weak gravitational lensing, the integrated Sachs-Wolfe effect, and the Sunyaev-Zel'dovich effect contained in the trispectrum. We incorporate these additional contributions to the covariance of a binned angular power spectrum of temperature anisotropies in the analysis of current and prospective data sets. Although recent experiments such as ACBAR and CBI are not particularly sensitive to these additional non-Gaussian effects, the interpretation of Planck and CMBPol anisotropy spectra will require an accounting of non-Gaussian covariance leading to a degradation in cosmological parameter estimates by up to 20% and 30%, respectively.

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arXiv2010

A collisional origin for the Leo ring

Extended HI structures around galaxies are of prime importance to probe galaxy formation scenarios. The giant HI ring in the Leo group is one of the largest and most intriguing HI structures in the nearby Universe. Whether it consists of primordial gas, as suggested by the apparent absence of any optical counterpart and the absence of an obvious physical connection to nearby galaxies, or of gas expelled from a galaxy in a collision is actively debated. We present deep wide field-of-view optical images of the ring region obtained with MegaCam on the CFHT. They reveal optical counterparts to several HI and UV condensations along the ring, in the g', r', and i' bands, which likely correspond to stellar associations formed within the gaseous ring. Analyzing the spectral energy distribution of one of these star-forming regions, we found it to be typical for a star-forming region in pre-enriched tidal debris. We then use simulations to test the hypothesis that the Leo ring results from a head-on collision between Leo group members NGC 3384 and M96. According to our model which is able to explain, at least qualitatively, the main observational properties of the system, the Leo ring is consistent with being a collisional ring. It is thus likely another example of extended intergalactic gas made-up of pre-enriched collisional debris.

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arXiv2010

No Evidence for Dark Energy Evolution from a global analysis of cosmological data

We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, $w(z)$. We constrain $w(z)$ in multiple redshift bins, utilizing the most recent data from Type Ia supernovae, the cosmic microwave background, baryon acoustic oscillations, the integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike other recent analyses, we find no significant evidence for evolving dark energy; the data remains completely consistent with a cosmological constant. We also study the extent to which the time-evolution of the equation of state would be constrained by a combination of current and future-generation surveys, such as Planck and the Joint Dark Energy Mission.

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arXiv2010

A Measurement of Cubic-Order Primordial Non-Gaussianity (g_{NL} and τ_{NL}) With WMAP 5-Year Data

We measure two higher-order power spectra involving weighted cubic and squared temperature anisotropy maps from WMAP 5-year data to study the trispectrum generated by primordial non-Gaussianity. Using these measurements combined with Gaussian and noise simulations, we constrain the cubic order non-Gaussianity parameters τ_{NL}, and g_{NL}. With V+W-band data out to l_{max}=600, we find -7.4 < g_{\rm NL}/10^5 < 8.2 and -0.6 < τ_{\rm NL}/10^4 < 3.3 improving the previous COBE-based limit on τ_{\rm NL} < 10^8 nearly four orders of magnitude with WMAP. We find that the ratio of trispectrum to bispectrum amplitude as captured by the ratio of τ_{\rm Nl}/(6f_{\rm NL}/5)^2 ranges from -3 to 21 at the 95% confidence level.

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arXiv2009

New Optimised Estimators for the Primordial Trispectrum

Cosmic microwave background studies of non-Gaussianity involving higher-order multispectra can distinguish between early universe theories that predict nearly identical power spectra. However, the recovery of higher-order multispectra is difficult from realistic data due to their complex response to inhomogeneous noise and partial sky coverage, which are often difficult to model analytically. A traditional alternative is to use one-point cumulants of various orders, which collapse the information present in a multispectrum to one number. The disadvantage of such a radical compression of the data is a loss of information as to the source of the statistical behaviour. A recent study by Munshi & Heavens (2009) has shown how to define the skew spectrum (the power spectra of a certain cubic field, related to the bispectrum) in an optimal way and how to estimate it from realistic data. The skew spectrum retains some of the information from the full configuration-dependence of the bispectrum, and can contain all the information on non-Gaussianity. In the present study, we extend the results of the skew spectrum to the case of two degenerate power-spectra related to the trispectrum. We also explore the relationship of these power-spectra and cumulant correlators previously used to study non-Gaussianity in projected galaxy surveys or weak lensing surveys. We construct nearly optimal estimators for quick tests and generalise them to estimators which can handle realistic data with all their complexity in a completely optimal manner. We show how these higher-order statistics and the related power spectra are related to the Taylor expansion coefficients of the potential in inflation models, and demonstrate how the trispectrum can constrain both the quadratic and cubic terms.

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arXiv2009

Cold gas and young stars in tidally-disturbed ellipticals at z=0

We present an analysis of the neutral hydrogen and stellar populations of elliptical galaxies in the Tal et al. (2009) sample. Our aim is to test their conclusion that the continuing assembly of these galaxies at z~0 is essentially gas-free and not accompanied by significant star formation. In order to do so, we make use of HI data and line-strength indices available in the literature. We look for direct and indirect evidence of the presence of cold gas during the recent assembly of these objects and analyse its relation to galaxy morphological fine structure. We find that >25% of ellipticals contain HI at the level of M(HI)>10^8 M(Sun), and that M(HI) is of the order of a few percent of the total stellar mass. Available data are insufficient to establish whether galaxies with a disturbed stellar morphology are more likely to contain HI. However, HI interferometry reveals very disturbed gas morphology/kinematics in all but one of the detected systems, confirming the continuing assembly of many ellipticals but also showing that this is not necessarily gas-free. We also find that all very disturbed ellipticals have a single-stellar-population-equivalent age <4 Gyr. We interpret this as evidence that ~0.5-5% of their stellar mass is contained in a young population formed during the past ~1 Gyr. Overall, a large fraction of ellipticals seem to have continued their assembly over the past few Gyr in the presence of a mass of cold gas of the order of 10% of the galaxy stellar mass. This material is now observable as neutral hydrogen and young stars.

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arXiv2009

Non-Gaussianity in WMAP Data Due to the Correlation of CMB Lensing Potential with Secondary Anisotropies

We measure the skewness power spectrum of the Cosmic Microwave Background (CMB) anisotropies optimized for a detection of the secondary bispectrum generated by the correlation of the CMB lensing potential with integrated Sachs-Wolfe effect and the Sunyaev-Zel'dovich effect. The covariance of our measurements is generated by Monte-Carlo simulations of Gaussian CMB fields with noise properties consistent with Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data. When interpreting multi-frequency measurements we also take into account the confusion resulting from unresolved radio point sources. We analyze Q, V and W-band WMAP 5-year raw and foreground-cleaned maps using the KQ75 mask out to l_max=600. We find no significant evidence for a non-zero non-Gaussian signal from the lensing-secondary correlation in all three bands and we constrain the overall amplitude of the cross power spectrum between CMB lensing potential and the sum of SZ and ISW fluctuations to be 0.42 \pm 0.86 and 1.19 \pm 0.86 in combined V and W-band raw and foreground-cleaned maps provided by the WMAP team, respectively. The point source amplitude at the bispectrum level measured with this skewness power spectrum is higher than previous measurements of point source non-Gaussianity. We also consider an analysis where we also account for the primordial non-Gaussianity in addition to lensing-secondary bispectrum and point sources. The focus of this paper is on secondary anisotropies. Consequently the estimator is not optimised for primordial non-Gaussianity and the limit we find on local non-Gaussianity from the foreground-cleaned V+W maps is f_NL = -13 \pm 62, when marginalized over point sources and lensing-ISW/SZ constributions to the total bispectrum.

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arXiv2009

No Evidence for Dark Energy Dynamics from a Global Analysis of Cosmological Data

We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, w(z). We constrain w(z) in multiple redshift bins, utilizing the most recent data from Type Ia supernovae, the cosmic microwave background, baryon acoustic oscillations, the integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike other recent analyses, we find no significant evidence for evolving dark energy; the data remains completely consistent with a cosmological constant. We also study the extent to which the time-evolution of the equation of state would be constrained by a combination of current- and future-generation surveys, such as Planck and the Joint Dark Energy Mission.

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arXiv2009

A Multi-Parameter Investigation of Gravitational Slip

A detailed analysis of gravitational slip, a new post-general relativity cosmological parameter characterizing the degree of departure of the laws of gravitation from general relativity on cosmological scales, is presented. This phenomenological approach assumes that cosmic acceleration is due to new gravitational effects; the amount of spacetime curvature produced per unit mass is changed in such a way that a universe containing only matter and radiation begins to accelerate as if under the influence of a cosmological constant. Changes in the law of gravitation are further manifest in the behavior of the inhomogeneous gravitational field, as reflected in the cosmic microwave background, weak lensing, and evolution of large-scale structure. The new parameter, $\varpi_0$, is naively expected to be of order unity. However, a multiparameter analysis, allowing for variation of all the standard cosmological parameters, finds that $\varpi_0 = 0.09^{+0.74}_{-0.59} (2σ)$ where $\varpi_0=0$ corresponds to a $Λ$CDM universe under general relativity. Future probes of the cosmic microwave background (Planck) and large-scale structure (Euclid) may improve the limits by a factor of four.

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arXiv2009

A Measurement of Primordial Non-Gaussianity Using WMAP 5-Year Temperature Skewness Power Spectrum

We constrain the primordial non-Gaussianity parameter of the local model f_{NL} using the skewness power spectrum associated with the two-to-one cumulant correlator of cosmic microwave background temperature anisotropies. This bispectrum-related power spectrum was constructed after weighting the temperature map with the appropriate window functions to form an estimator that probes the multipolar dependence of the underlying bispectrum associated with the primordial non-Gaussianity. We also estimate a separate skewness power spectrum sensitive more strongly to unresolved point sources. When compared to previous attempts at measuring the primordial non-Gaussianity with WMAP data, our estimators have the main advantage that we do not collapse information to a single number. When model fitting the two-to-one skewness power spectrum we make use of bispectra generated by the primordial non-Gaussianity, radio point sources, and lensing-secondary correlation. We analyze Q, V and W-band WMAP 5-year data using the KQ75 mask out to l_{max}=600. Using V and W-band data and marginalizing over model parameters related to point sources and lensing-secondary bispectrum, our overall and preferred constraint on f_{NL} is 11.0\pm23.7 at the 68% confidence level (-36.4 < f_{NL} < 58.4 at 95% confidence). We find no evidence for a non-zero value of f_{NL} even marginally at the 1σlevel.

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arXiv2009

ESO 381-47, an early-type galaxy with extended HI and a star forming ring

ESO 381-47 is an early type galaxy with an extended HI disk. GALEX and very deep optical images reveal a distinct stellar ring far outside the optical body with a diameter of ~30 kpc, which has undergone recent star formation at 1.8 x 10^-4 Msun/yr/kpc^-2, consistent with other new results which detect low level star formation below the traditional Kennicutt relation in the outer parts of spiral galaxies. The morphology of this galaxy resembles the recently identified class of ultraviolet objects called extended ultraviolet disks, or XUV-disks. New HI observations of this galaxy taken at the ATCA and in the CnB array at the VLA show that the cold gas lies in an extended (diameter ~90 kpc) ring around the central S0 galaxy. The HI data cube can be well modeled by a warped ring. The faint ionized gas in the inner parts of the galaxy is kinematically decoupled from the stars and instead appears to exhibit velocities consistent with the rotation of the HI ring at larger radius. The peak of the stellar ring, as seen in the optical and UV, is slightly displaced to the inside relative to the peak of the HI ring. We discuss the manner in which this offset could be caused by the propagation of a radial density wave through an existing stellar disk, perhaps triggered by a galaxy collision at the center of the disk, or possibly due to a spiral density wave set up at early times in a disk too hot to form a stellar bar. Gas accretion and resonance effects due to a bar which has since dissolved are also considered to explain the presence of the star forming ring seen in the GALEX and deep optical data.

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arXiv2009

The Case for Deep, Wide-Field Cosmology

Much of the science case for the next generation of deep, wide-field optical/infrared surveys has been driven by the further study of dark energy. This is a laudable goal (and the subject of a companion white paper by Zhan et al.). However, one of the most important lessons of the current generation of surveys is that the interesting science questions at the end of the survey are quite different than they were when the surveys were being planned. The current surveys succeeded in this evolving terrain by being very general tools that could be applied to a number of very fundamental measurements. Likewise, the accessibility of the data enabled the broader cosmological and astronomical community to generate more science than the survey collaborations could alone. With that in mind, we should consider some of the basic physical and cosmological questions that surveys like LSST and JDEM-Wide will be able to address.

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