J. M. Diego

The CMB cold spot: texture, cluster or void?

ABSTRACT The non-Gaussian cold spot found in the WMAP data has created controversyabout its origin. Here we calculate the Bayesian posterior probability ratios for threedifferent models that could explain the cold spot. A recent work claimed that theSpot could be caused by a cosmic texture, while other papers suggest that it couldbe due to the gravitational effect produced by an anomalously large void. Also theSunyaev-Zeldovich effect caused by a cluster is taken into account as a possible origin.We perform a template fitting on a 20 ◦ radius patch centered at Galactic coordi-nates (b = −57 ◦ ,l = 209 ◦ ) and calculate the posterior probability ratios for the voidand Sunyaev-Zeldovich models, comparing the results to those obtained with texture.Taking realistic priors for the parameters, the texture interpretation is favored, whilethe void and Sunyaev-Zeldovich hypotheses are discarded. The temperature decre-ment produced by voids or clusters is negligible considering realistic values for theparameters.Key words: methods: data analysis - cosmic microwave background

A Geometrically Supported z ~ 10 Candidate Multiply Imaged by the Hubble Frontier Fields Cluster A2744

The deflection angles of lensed sources increase with their distance behind a given lens. We utilize this geometric effect to corroborate the z_phot ≃ 9.8 photometric redshift estimate of a faint near-IR dropout, triply imaged by the massive galaxy cluster A2744 in deep Hubble Frontier Fields images. The multiple images of this source follow the same symmetry as other nearby sets of multiple images that bracket the critical curves and have well-defined redshifts (up to z_spec ≃ 3.6), but with larger deflection angles, indicating that this source must lie at a higher redshift. Similarly, our different parametric and non-parametric lens models all require this object be at z ≳ 4, with at least 95% confidence, thoroughly excluding the possibility of lower-redshift interlopers. To study the properties of this source, we correct the two brighter images for their magnifications, leading to a star formation rate of ~0.3 M_☉ yr^(−1), a stellar mass of ~4 × 10^7 M_☉, and an age of ≲220 Myr (95% confidence). The intrinsic apparent magnitude is 29.9 AB (F160W), and the rest-frame UV (~1500 A) absolute magnitude is M_UV, AB = −17.6. This corresponds to ~0.1 L*_(z=8) (~0.2 L*_(z=10), adopting dM*/dz ~ 0.45), making this candidate one of the least luminous galaxies discovered at z ~ 10.

Combined reconstruction of weak and strong lensing data with wslap

We describe a method to estimate the mass distribution of a gravitational lens and the position of the sources from combined strong and weak lensing data. The algorithm combines weak and strong lensing data in a unified way producing a solution which is valid in both the weak and the strong lensing regimes. The method is non-parametric, allowing the mass to be located anywhere in the field of view. We study how the solution depends on the choice of basis used to represent the mass distribution. We find that combining weak and strong lensing information has two major advantages: it alleviates the need for priors and/or regularization schemes for the intrinsic size of the background galaxies (this assumption was needed in previous strong lensing algorithms) and it reduces (although does not remove) biases in the recovered mass in the outer regions where the strong lensing data are less sensitive. The code is implemented into a software package called Weak & Strong Lensing Analysis Package (WSLAP) which is publicly available at http://darwin.cfa.harvard.edu/SLAP/.

Non-parametric inversion of strong lensing systems

We revisit the issue of non-parametric gravitational lens reconstruction and present a new method to obtain the cluster mass distribution using strong lensing data without using any prior information on the underlying mass. The method relies on the decomposition of the lens plane into individual cells. We show how the problem in this approximation can be expressed as a system of linear equations for which a solution can be found. Moreover, we propose to include information about the null space. That is, we make use of the pixels in which we know there are no arcs above the sky noise. The only prior information is an estimation of the physical size of the sources. No priors on the luminosity of the cluster or shape of the haloes are needed, making the results very robust. In order to test the accuracy and bias of the method we make use of simulated strong lensing data. We find that the method reproduces accurately both the lens mass and source positions and provides error estimates.

Statistics of extreme objects in the Juropa Hubble Volume simulation

We present the first results from the JUropa huBbLE volumE (Ju bilee) project, based on the output from a large N-body, dark matter-only cosmological simulation with a volume of V = (6 h −1 Gpc) 3 , containing 6000 3 particles, performed within the concordance �CDM cosmological model. The simulation volume is sufficient to probe extremely large length scales in the universe, whilst at the same time the par ticle count is high enough so that dark matter haloes down to 1.5 × 10 12 h −1 M⊙ can be resolved. At z = 0 we identify over 400 million haloes, and the first haloes in the simulatio n form at z = 11. We present an all-sky map of the Integrated Sachs Wolfe signal calculated from the gravitational potential in the box between z = 0 1.4. The cluster mass function is derived using three different halofinders and compared to fitting functions in the literatu re, with results being consistent with previous studies across most of the mass-range of the simulation. We compare simulated clusters of maximal mass across redshifts and find that our data fits well with observed masses of extreme objects, and we explicitly confirm that the Poisson distribution is very good at describing the distribution of extremely rare objec ts. We find that objects like the Bullet cluster exist in the far-tail of the distribution of m ergers in terms of relative collisional speed, perhaps implying a tension with �-CDM. We show the level to which cosmic variance can be expected to affect number counts of clusters in volumes smaller than (6 h −1 Gpc) 3 via the cluster abundance function. For example a (500 h −1 Mpc) 3 volume at redshift zero would see a 10%+ error in number counts of dark matter haloes with masses equal to or greater than 4 × 10 14 h −1 M⊙. We derive the number counts of voids in the simulation box for z =0, 0.5 and 1. Defining voids as spherical volumes containing n o haloes with a mass over 10 13 h −1 M⊙ the void function shows a steep cut-off at a scale radius of � 40 h −1 Mpc. For voids defined with an aggressive mass threshold of 5 × 10 14 h −1 M⊙ we find that there are no voids larger in radius than � 250 h −1 Mpc. These results place the lower limit on the scale at which the universe can be considered approximately homogeneous at a few hundred Mpc, and also have implications for the expected sizes of voids that we should observe in the universe in the �-CDM model.

Free-form lensing implications for the collision of dark matter and gas in the frontier fields cluster MACS J0416.1−2403

JMD acknowledges support of the consolider project CAD2010-00064 and AYA2012-39475-C02-01 funded by the Ministerio de Economia y Competitividad.

Constraining our Universe with X-ray and optical cluster data

We have used recent X-ray and optical data in order to impose some constraints on the cosmology and cluster scaling relations. Generically, two kinds of hypotheses define our model. First, we consider that the cluster population is well described by the standard Press–Schechter (PS) formalism, and secondly, these clusters are assumed to follow scaling relations with mass: temperature–mass (T–M) and X-ray luminosity–mass (Lx–M). In contrast with many other authors we do not assume specific scaling relations to model cluster properties such as the usual T–M virial relation or an observational relation or an observational determination of the Lx–T relation. Instead we consider general unconstrained parameter scaling relations. With the previous model (PS plus scalings) we fit our free parameters to several X-ray and optical data sets with the advantage over preceding works that we consider all the data sets at the same time. This prevents us from being inconsistent with some of the available observations. Among other interesting conclusions, we find that only low-density universes are compatible with all the data considered and that the degeneracy between Ωm and σ8 is broken. Also we obtain interesting limits on the parameters characterizing the scaling relations.

THREE-DIMENSIONAL MULTI-PROBE ANALYSIS OF THE GALAXY CLUSTER A1689*

The work is partially supported by the Ministry of Science and Technology of Taiwan under the grant MOST 103-2112-M-001-030-MY3. M. S. acknowledges financial contributions from contracts ASI/INAF I/023/ 12/0, by the PRIN MIUR 2010–2011 “The dark universe and the cosmic evolution of baryons: from current surveys to Euclid” and by the PRIN INAF 2012 “The universe in the box: multiscale simulations of cosmic structure.” M. N. acknowledges financial support from PRIN INAF 2014. J. M. D. acknowledges support of the consolider project CSD2010-00064 and AYA2012-39475-C02-01 funded by the Ministerio de Economia y Competitividad. N. O. is supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (26800097). This work was partially supported by “World Premier International Research Center Initiative (WPI Initiative)” and the Funds for the Development of Human Resources in Science and Technology under MEXT, Japan. This research was performed while T. M. held a National Research Council Research Associateship Award at the Naval Research Laboratory (NRL). We thank John Carlstrom, Megan Gralla, Marshall Joy, Dan Marrone, and the entire SZA and OVRO/BIMA teams for providing the SZA and OVRO/BIMA data used in this study. Support for the SZA observations presented in this work was provided by NSF through award AST-0838187 and PHY-0114422 at the University of Chicago. The OVRO and BIMA observations presented here were supported by National Science Foundation grants AST 99-81546 and 02-28963.

On the formation of cold fronts in massive mergers

Using adiabatic hydrodynamical simulations, we follow the evolution of two symmetric cold fronts forming in the remnant of a violent z= 0.3 massive cluster merger. Because the fronts develop after the first passage of the two gas cores of the merging subclusters, and because they soon move ahead of their associated dark matter cores, both the structure and the location of our simulated cold fronts may correspond to a stage that is later than that of most cold fronts observed so far. The cold fronts are preceded by a roughly spherical shock that originates in the centre of the cluster and disappears in the outer regions after 1.6 Gyr. The cold fronts last longer, until z∼ 0. We follow the spatial evolution of the gas of the subcluster cores, and find that a fraction of this gas is liberated in the intracluster medium after core passage, but mainly at apocentre, and that it does not fall back onto the cluster centre. Conversely, we trace back the low-temperature gas constituting the fronts and find that it is initially associated with the two dense cores of the merging clusters. In addition, we find some evidence for discontinuity of the gas velocity field across the edge of the forming cold fronts, suggesting the presence of a contact discontinuity there. In the light of other recent work, we then speculate on the physical mechanism resulting in the cold fronts. We suggest that sloshing induced by strongly varying ram pressure along the subclusters orbit and/or spatial segregation between the dark matter and gas components of the cores of the subclusters results in strong tidal forces on the gas, and that these forces could be responsible for the deposition of part of the cold dense gas in the surrounding hot intracluster medium. This deposited gas then expands, cools down further, and constitutes the cold fronts.

Self-similarity and universality of void density profiles in simulation and SDSS data

The stacked density profile of cosmic voids in the galaxy distribution provides an important tool for the use of voids for precision cosmology. We study the density profiles of voids identified using the ZOBOV watershed transform algorithm in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. We compare different methods for reconstructing density profiles scaled by the void radius and show that the most commonly used method based on counts in shells and simple averaging is statistically flawed as it underestimates the density in void interiors. We provide two alternative methods that do not suffer from this effect; one based on Voronoi tessellations is also easily able to account from artefacts due to finite survey boundaries and so is more suitable when comparing simulation data to observation. Using this method, we show that the most robust voids in simulation are exactly self-similar, meaning that their average rescaled profile does not depend on the void size. Within the range of our simulation, we also find no redshift dependence of the mean profile. Comparison of the profiles obtained from simulated and real voids shows an excellent match. The mean profiles of real voids also show a universal behaviour over a wide range of galaxy luminosities, number densities and redshifts. This points to a fundamental property of the voids found by the watershed algorithm, which can be exploited in future studies of voids.