Francisco-Shu Kitaura

13/11/2015

Sound waves from the primordial fluctuations of the Universe imprinted in the large-scale structure, called baryon acoustic oscillations (BAOs), can be used as standard rulers to measure the scale of the Universe. These oscillations have already been detected in the distribution of galaxies. Here we propose to measure BAOs from the troughs (minima) of the density field. Based on two sets of accurate mock halo catalogues with and without BAOs in the seed initial conditions, we demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but is clearly detected from overlapping voids. The latter represent an estimate of all troughs of the density field. We compute them from the empty circumspheres centres constrained by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models based on an unprecedented large set of detailed simulated void catalogues are remarkably well confirmed by observational data. We use the largest recently publicly available sample of Luminous Red Galaxies from SDSS-III BOSS DR11 to unveil for the first time a >3σ BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their centres represent the most quiet places in the Universe, keeping in memory the cosmos origin, and providing a new promising window in the analysis of the cosmological large-scale structure from galaxy surveys.

9/11/2015

By using the best available measurements of the cosmic microwave background (CMB) from the Planck satellite, Dr. Carlos Hernández Monteagudo from the Centro de Estudios de Física del Cosmos de Aragón (CEFCA) and his collaborators have detected vast amounts of hidden baryonic matter around middle-size galaxies in the local universe. To arrive at this new result, the team has used the latest Planck data release and data from the Sloan Digital Sky Survey.

This new study solves the problem of the missing baryons around 200.000 local galaxies, and also contributes to the understanding of the distribution of baryonic matter in galaxies, groups and clusters of galaxies, an essential ingredient to know how these objects form and evolve.

Baryons are particles, such as protons and neutrons, that, together with electrons, make up the atoms found in the Universe. Nowadays, It is well known that around 90% of all baryons created in the first moments of the Universe after the Big Bang reside in the form of a diffuse, hot and ionized gas, esentially composed of protons and free electrons. However, only a small part of this gas, the hottest fraction, could be detected up to now.

By observing the fluctuations of the CMB light along the direction of those galaxies, the team has been able to detect clouds of ionized gas extending to distances significantly larger than the size of the galaxies. This corresponds to the so-called "missing" or "hidden" baryons surrounding those galaxies, whose spatial distribution is very close to the distribution expected for dark matter around those objects. The dark matter is the dominant form of matter in the Universe, which has not been directly detected or characterized yet.

“We have discovered a kick experienced by the CMB photons when they encounter moving electrons in ionized clouds. This leads to a tiny fluctuation in the temperature of the CMB around each of those galaxies, which we have nevertheless managed to detect statistically after stacking the CMB measurements in the direction of all of our 200,000 galaxies” states Dr. Hernández-Monteagudo. The high quality of Planck data allowed the team to reveal the presence of ionized gas out to a distance of 20 to 30 times the typical distance of luminous matter to the center of the galaxy. "Within those distances we have found as much gas as theory predicts we should find", he concludes.

This work, led by CEFCA, has been published in Physical Review Letters, in collaboration with researchers working in other institutions in Spain (IFCA in Cantabria, IAC in Spain) and other countries (UK, Germany and France).

C. Hernández-Monteagudo, Yin-Zhe Ma, F. S. Kitaura, W. Wang, R. Génova-Santos, J. Macías-Pérez, and D. Herranz. Evidence of the Missing Baryons from the Kinematic Sunyaev-Zeldovich Effect in Planck Data. Physical Review Letters.

23/09/2015

We reproduce the galaxy clustering catalogue from the SDSS-III Baryon Oscillations Spectroscopic Survey Final Data Release (BOSS DR11&DR12) with high fidelity on all relevant scales in order to allow a robust analysis of baryon acoustic oscillations and redshift space distortions. We have generated (6,000) 12,288 MultiDark patchy BOSS (DR11) DR12 light-cones corresponding to an effective volume of ∼192, 000 [h−1 Gpc]3 (the largest ever simulated volume), including cosmic evolution in the redshift range from 0.15 to 0.75. The mocks have been calibrated using a reference galaxy catalogue based on the Halo Abundance Matching modelling of the BOSS DR11&DR12 galaxy clustering data and on the data themselves. The production follows three steps. First, we apply the patchy-code to generate a dark matter field and an object distribution including nonlinear stochastic galaxy bias. Second, we run the halo/stellar distribution reconstruction hadron-code to assign masses to the various objects. This step uses the mass distribution as a function of local density and non-local indicators (i.e., tidal- field tensor eigenvalues and relative halo-exclusion separation for massive objects) from the reference simulation applied to the corresponding patchy dark matter and galaxy distribution. Finally, we apply the sugar-code to build the light-cones. The result- ing MultiDark patchy mock light-cones reproduce the number density, selection function, survey geometry, and in general within 1-σ, for arbitrary stellar mass bins, the power spectrum up to k = 0.3 h Mpc−1, the two-point correlation functions down to a few Mpc scales, and the three-point statistics of the BOSS DR11&DR12 galaxy samples.

31/07/2015

We present a Bayesian reconstruction method which maps a galaxy distribution from redshift- to real-space inferring the distances of the individual galaxies. The method is based on sampling density fields assuming a lognormal prior with a likelihood mod- elling nonlinear stochastic bias. Coherent redshift-space distortions are corrected in a Gibbs-sampling procedure by moving the galaxies from redshift- to real-space ac- cording to the peculiar motions derived from the recovered density field using linear theory. The virialised distortions are corrected by sampling candidate real-space po- sitions along the line of sight, which are compatible with the bulk flow corrected redshift-space position adding a random dispersion term in high density collapsed regions (defined by the eigenvalues of the Hessian). This approach presents an alternative method to estimate the distances to galaxies using the three dimensional spatial information, and assuming isotropy. Hence the number of applications is very broad. In this work we show the potential of this method to constrain the growth rate up to k ∼ 0.3h Mpc−1. Furthermore it could be useful to correct for photo-metric redshift errors, and to obtain improved BAO reconstructions.

13/04/2015

By looking at the kinetic Sunyaev-Zeldovich effect (kSZ) in Planck nominal mission data, we present a significant detection of baryons participating in large-scale bulk flows around central galaxies (CGs) at redshift z≈0.1. We estimate the pairwise momentum of the kSZ temperature fluctuations at the positions of the CGC (Central Galaxy Catalogue) samples extracted from Sloan Digital Sky Survey (DR7) data. For the foreground-cleaned maps, we find 1.8-2.5σ detections of the kSZ signal, which are consistent with the kSZ evidence found in individual Planck raw frequency maps, although lower than found in the WMAP-9yr W band (3.3σ). We further reconstruct the peculiar velocity field from the CG density field, and compute for the first time the cross-correlation function between kSZ temperature fluctuations and estimates of CG radial peculiar velocities. This correlation function yields a 3.0-3.7σ detection of the peculiar motion of extended gas on Mpc scales, in flows correlated up to distances of 80-100 h−1 Mpc. Both the pairwise momentum estimates and kSZ temperature-velocity field correlation find evidence for kSZ signatures out to apertures of 8 arcmin and beyond, corresponding to a physical radius of >1 Mpc, more than twice the mean virial radius of halos. This is consistent with the predictions from hydro simulations that most of the baryons are outside the virialized halos. We fit a simple model, in which the temperature-velocity cross-correlation is proportional to the signal seen in a semi-analytic model built upon N-body simulations, and interpret the proportionality constant as an "effective" optical depth to Thomson scattering. We find τT=(1.4±0.5)×10−4; the simplest interpretation of this measurement is that much of the gas is in a diffuse phase, which contributes little signal to X-ray or thermal SZ observations.

27/01/2015

We use the constrained simulations made with the reconstructed initial conditions from KIGEN to study the environment of different type of galaxies. In particular we study the environment of extremely metal poor galaxies.

25/01/2015

We have investigated the dependence of halo mass and environment. This permits an accurate modelling of BAOs for different population of objects.

23/12/2014

Unprecedented reconstruction of cosmic flows in the Local Universe based on galaxy redshift data

2011-

I work on developing and applying technique to recover the phase space (matter positions and velocies) at any given cosmic time corresponding to the observed distribution of galaxies. In particular I have developed the Kigen code.

11/08/2014

Metin Ata and myself have worked on the Bayesian formalism of non-Poissonian likelihoods extending the Argo code to model the stochastic bias component of the halo or galaxy distribution.

04/07/2014

We present a method to constrin the three point statistics of a halo or galaxy distribution with perturbation theory and nonlinear stochastic biasing

11/07/2013

The BAOs can be used as standard rulers to measure the Universe and its cosmic expansion. I work on accurate theoretical models to describe the BAO features and on reconstruction techniques to optimally measure them. I use for such studies all my different main computer codes: Patchy, Argo and Kigen.

11/07/2013

There is only one Universe, when astronomers try to infer quantities from galaxy surveys, they require many realistic synthetic galaxy catalogues (like many different realisations of the Universe) to estimate the uncertainties in their measurements. I work on modeling the halo/galaxy distribution from the underlying dark matter field. I have developed the Patchy code, which does this in an efficient way using Lagrangian perturbation theory and statistical descriptions of the halo/galaxy field.

24/04/2013

Steffen Heß and myself have worked on constrained simulations of the Local Universe using 2MASS survey data. Here we use the Kigen code to reconstruct the primordial fluctuations with Augmented Lagrangian Perturbation Theory. We take special care to jointly reconstruct the peculiar velocity field.

14/12/2012

We have developed a one step gravity solver, which alleviates the problems induced by shell crossing in the common Lagrangian perturbation theory.

14/12/2010

The large-scale structure of the Universe is non-Gaussian and includes higher order correlation functions, which require complex statistical models. I work on different techniques and models, like the Multivariate Edgeworth expansion of log-normal fields.

I also work on non-Poisson likelihoods.