The Frontiers seen with Hubble
Jean-Paul Richard Kneib (Observatoire Sauverny)
In the course of the past few decades, gravitational lensing has proven to be an exceptionally powerful tool for studies of faint objects at the edge of the observable Universe, as well as for the characterisation of the mass distributions in lensing systems. Generating significant gravitational amplification over areas of several square arcmin, massive galaxy clusters in particular are natural telescopes that allow us to probe the distant universe to unprecedented depth. Recognising the enormous potential of the gravitational amplification provided by massive clusters and capitalising on the results of all-sky surveys designed specifically to find these rare systems, Hubble and Spitzer are currently conducting extremely deep observations in visible, near-infrared and mid-infrared of six massive clusters and "blank" parallel fields: the Frontier Fields project. The primary science goal of the Frontier Fields project is to probe the population of high-redshift galaxies to luminosity limits that are currently unattainable without gravitational magnification; highly accurate mass maps of the lensing clusters are both a byproduct of the observation and a crucial prerequisite for their full scientific exploitation. Additional research facilitated by the FF initiative includes topics as diverse as accelerated galaxy evolution in high-density environments and studies of transient sources in both the cluster and blank flanking fields. I will review the most important discoveries of the Frontier Fields and discuss the challenges for the future.
Cosmology at the percent level or better with redshift surveys
Jean-Paul Richard Kneib (Observatoire Sauverny)
Wide field spectroscopic observations is emerging as a new powerful tool to constrain cosmology at the percent level or better. In this presentation, I will review present results and discuss current and future experiments. The current major experiment, eBOSS, will precisely measure the expansion history of the Universe throughout eighty percent of cosmic history, back to when the Universe was less than three billion years old, and improve constraints on the nature of dark energy. eBOSS concentrates its efforts on the observation of luminous red galaxies, emission line galaxies and quasars, in a redshift range currently left completely unexplored by previous 3D maps of large-scale structure of the Universe. In filling this gap, eBOSS will create the largest volume survey of the Universe to date and explore the epoch when the Universe was transitioning from deceleration due to the effects of gravity, to the current epoch of acceleration. Future projects (from ground and space) are developing new instrumentation to further probe at a higher density the galaxy and quasar distribution to build a more complete 3D-map of the large scale structure in the Universe. I will discuss the progresses and challenges of these future experiments.
Observational Constraints on the Growth and Evolution of AGN
Franz E. Bauer (Pontificia Universidad Católica de Chile)
A key goal of high-energy astrophysics has been to understand the composition of the Cosmic X-ray Background and more specifically how the growth of supermassive black holes (SMBHs) and the subsequent evolution of active galactic nuclei (AGN) contribute to it. The further realization that SMBHs reside in the centers of most galaxies and can potentially impact galactic processes through energy and momentum feedback has made their study important within the greater scheme of galaxy evolution as well. Optical quasar studies provide us with a basic picture, such objects fail to track obscured accretion, which is thought to be where the bulk of SMBH growth and evolution occur. A number of recent surveys at hard X-ray and mid-infrared wavelengths now provide windows to track such obscured growth. I will highlight in particular the constraints that we have recently amassed from Spitzer, WISE, Chandra, XMM and most recently NuSTAR and what they tell us about the formation and evolution of AGN, as well as what our prospects are for finding high-z AGN and their progenitor seeds in the coming years.
Evolution of Galaxies Out to the Reionization Epoch
Franz E. Bauer (Pontificia Universidad Católica de Chile)
The past two decades have witnessed tremendous advances in finding and characterizing star-forming galaxies at high redshifts across the electromagnetic spectrum, allowing us to form a rough impression of how galaxies evolve, e.g., in terms of their stellar and gas content, black hole masses, environments. We now know that the star formation rate rose dramatically at early times to peak at z~2 (~3 Gyr after the Big Bang) and then declined exponentially to the present day. Thus we must look to high redshift for answers to many critical questions. In this respect, substantial effort has gone into probing objects both in the most extreme and rapid star-forming environments (i.e., in submm galaxies or SMGs), in order to learn how and why stars can form so rapidly, and at the highest-redshifts, to understand the epoch of reionization and how the earliest observable galaxies form. I will review some of the progress we have made in both areas and how we may be able to improve upon this in the near future, particularly with surveys like the ongoing Frontier Fields project.
Black hole growth and the Eddington limit
Marta Volonteri (Institut d'Astrophysique de Paris)
Very often the Eddington luminosity is translated into a limit on the accretion rate sustainable by a black hole during its growth. I will discuss the difference between Eddington luminosity and Eddington accretion rate, and when the Eddington limit is not, in fact, a limit. I will apply the argument to high-redshift massive black holes, to illustrate how their growth may proceed much faster than commonly thought.
Black hole "seed" formation
Marta Volonteri (Institut d'Astrophysique de Paris)
Massive black holes are routinely detected in the centers of nearby galaxies, and are known to power quasars across cosmic time. One of the main unknowns is how massive black holes formed in the first place. I will critically review formation models, and discuss diagnostics to probe these mechanisms.
Records from Primordial Gravitational Waves and Cosmic Accelerations in the CMB polarization.
Carlo Baccigalupi
(International School for Advanced Studies)
We review the physics of CMB polarization, focusing on the most important effects coming from Cosmological Gravitational Waves, and Gravitational Lensing. We discuss how those signals are related to the physics of the Early Universe and Dark Energy, respectively, and focus on their contribution in particular to the B modes of CMB polarization anisotropies.
CMB B modes: Status of Observations, Implications and Expectations for the near future.
Carlo Baccigalupi
(International School for Advanced Studies)
We discuss the status of observations for CMB B modes, focusing on the significant recent progresses, We discuss the existing constraints on Primordial Gravitational Waves from B modes on the degree scales, the challenge represented by foreground contamination, and the ongoing improvements of experiments to reach the planned sensitivity. We also describe the current measurements of Gravitational Lensing and the implications for the dynamics of the Dark Energy in particular, discussing the expectations for the near future and the ultimate constraints which can be obtained from Large Scale Structure measurements. We stress how this aspect, and the one concerning the Early Universe through Cosmological Gravitational Waves, are closely related in CMB B modes observations.
Modeling Dark Energy and Modified Gravity
Martin Kunz (Department of Theoretical Physics of the University of Geneva)
The current standard model of cosmology, Lambda-CDM, has been extremely successful. However, the cosmological constant suffers from several theoretical problems, which motivates the search for alternative theories that can explain the observed accelerated expansion of the Universe. We will review a range of extensions of the standard model, and ways to systematically explore the space of possible theories of dark energy and modifications of General Relativity. We will also look at ways to try to detect deviations from GR in a model-independent way.
Constraints on Dark Energy and Modified Gravity models
Martin Kunz (Department of Theoretical Physics of the University of Geneva)
We use the recent Planck data together with observations of weak lensing and redshift space distortions to look for a deviation from a cosmological constant, based on the discussion in the first presentation. We will look at constraints on general approaches like (a subset of) effective field theory operators and phenomenological parameterizations. In addition, we will also consider specific models like canonical scalar fields, early dark energy, f(R) and coupled models. Time permitting, we will also look into the future where we can expect data from the Euclid satellite and the SKA radio telescope.
Type Ia supernovae detection with the J-PAS observatory
Beatriz Blanco Siffert (IF-UFRJ)
Although type Ia supernovae have been vastly used as standard candles to measure cosmological distances and study the expansion history of the Universe, many of the basic properties of these explosions are still not well understood, including their very nature. Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) will be based on an observatory under construction near the city of Teruel, in Spain, which will have two telescopes: a main one with 2,5 m diameter and an auxiliary one with 80 cm, and a camera equipped with a 56 narrow band filter system in the optical. In this talk, I will describe the main characteristics of the main J-PAS and the auxiliary J-PLUS surveys, and show the steps needed for the pipeline we are building to detect supernovae in each case.
Protoclusters and the establishment of the galaxy-environment relation
Karín Menéndez-Delmestre (Observatório do Valongo, UFRJ)
In a cold dark matter universe, dark matter is expected to collapse into halo potential wells into which baryonic matter falls along filamentary and sheet-like structures to form protoclusters, which ultimately virialize into the clusters of galaxies that we see today. Local studies show that galaxy properties are linked to the galaxy number density within the local environment. A classic example is the morphology-density relation – the preferential location of passive galaxies in the densest environments (close to the centers of clusters), or equivalently, the lack of actively star-forming galaxies in these dense regions. The physical origin of this relation is still controversial: does this relation arise early in the formation of these galaxies? Or, are there environmental processes that set local conditions to orchestrate the subsequent internal evolution of these galaxies? Or both? This is the well-known nature vs. nurture dilemma. To understand the origin of the galaxy-environment relation, one needs to look back at the epoch of galaxy formation, where initial conditions likely set the stage for the establishment of this relation. In spite of important observational and theoretical progress, outstanding challenges remain in understanding the link between large-scale structure and galaxy evolution, partly due to difficulties in identifying and characterizing overdense regions in the distant universe. I will provide a brief review on the search for protoclusters and share some of my ongoing work on the characterization of overdense regions around extreme starburst galaxies at the peak of galaxy formation.
Dark Matter in the Milky Way
Fabio Iocco (ICTP-South American Institute for Fundamental Research and Instituto de Física Teórica - UNESP)
The presence of dark matter on a wide range of astrophysical scales is one of the observational pillars of the current LambdaCDM cosmological model. In particular, spiral galaxies are known to be dark matter dominated systems, and one of the most outstanding astrophysical proofs of its existence. Yet, retrieving information about the the dark matter distribution in our very own spiral Galaxy, the Milky Way, is quite challenging. This quantity is crucial for both testing the paradigm of the LambdaCDM Universe, and as input for many of the experiments, both ground- and space-based, that are engaged in the search of the very nature of dark matter. In this talk I will present the results of recent analysis that prove evidence of dark matter in the inner region of the Milky Way, a remarkable confirmation of what expected from simulations of Galaxy Formation within the LambdaCDM Universe. I will also show how different analysis of the dataset assembled, permit to derive new and critical information on the dark matter profile of the Milky Way. I will finally comment on the prospects for the future of this field.
From quantum to classical instability in relativistic stars
André G. S. Landulfo (Universidade Federal do ABC)
It has been shown that gravitational fields produced by realistic classical-matter distributions can force quantum vacuum fluctuations of some nonminimally coupled free scalar fields to undergo a phase of exponential growth. The consequences of this unstable phase for the background spacetime have not been addressed so far due to known difficulties concerning backreaction in semiclassical gravity. It seems reasonable to believe, however, that the quantum fluctuations will “classicalize” when they become large enough, after which backreaction can be treated in the general-relativistic context. In this talk we will show the emergence of a classical regime out of the quantum field evolution during the unstable phase. By studying the appearance of classical correlations and loss of quantum coherence, we show that by the time backreaction becomes important the system already behaves classically. Consequently, the gravity-induced instability leads naturally to initial conditions for the eventual classical description of the backreaction. Our results give support to previous analyses which treat classically the instability of scalar fields in the spacetime of relativistic stars, regardless of whether the instability is triggered by classical or quantum perturbations.
Relativistic Outflows From Massive Black Holes
Rodrigo Nemmen (IAG-USP)
Supermassive black holes in active galactic nuclei (AGN) are key actors in our modern view of the cosmos. How these black holes power extremely energetic, relativistic outflows called jets is an outstanding issue. I will review recent observational results which suggest that the central engines in jet-producing AGNs have huge energy-efficiencies, requiring extraction of rotational energy of the black hole. I will outline an emerging model for jetted AGNs inspired by general relativistic MHD simulations.
Fetures in the spectrum of primordial perturbations, constraints from CMB and SDSS data and forecast for the J-PAS experiment
Micol Benetti (ON)
The recent results from the Planck satellite on the Cosmic Microwave Background (CMB) angular power spectrum shows small but significant features at low multipoles (l~20-60). These features could be explained supporting the Standard Cosmological Model with the inflationary paradigm and assuming a particular class of inflationary models with step-like inflationary potentials. The inflationary potential shape we present is basically a so-called “chaotic potential” type, but here we consider a non constant effective inflaton mass and we parametrize its changes with the introduction of a step function. The variation of the inflaton effective mass produces, in the primordial inflationary potential, a localized oscillation that is able to produce oscillations at large scales in the anisotropy power spectrum of the CMB, improving the fit of the LCDM model. Since it is the same curvature perturbations that set the initial conditions for CMB anisotropies and large-scale structure (LSS) distributions, the primordial oscillatory signals should be imprinted in all the observables of CMB anisotropy and LSS tracers, like CMB spectra, bispectra, galaxy spectra, etc. Therefore, we investigated these models using combined data from the CMB and LSS, since these are independent data able to show the effects of primordial fluctuations at different cosmological scales. Our results shows an improvement of the precision on the step parameters value using both the SDSS survey data and CMB data respect to the same analysis using only CMB data. We also present a forecast for the J-PAS experiment, a new astronomical facility due to a strict Spanish-Brazilian collaboration. It will be dedicated to mapping the observable Universe in 59 colors and will be able to produce high-quality images and a unique spectral resolution, Our forecast about its data shows a great improvement on the step parameter determination and the Chi-squared test shows a big preference for the step-like model respect to the LCDM model.
Eternal Inflation and the effects of dissipation and noise
Rudnei Ramos (DFT-UERJ)
Nonisentropic inflation models attempt to fully account for the quantum effects that other field degrees of freedom, other than the inflaton field, might cause on the inflaton dynamics. In particular, it is known that these quantum effects can produce both quantum and thermal stochastic noise and dissipation terms in the inflaton's equation of motion. Here we analyze how these quantum and thermal effects can alter the possibility for producing eternal inflation in the context of different potentials for the inflaton.
Constraining Cosmic Acceleration from Structure Observables
Marcos Lima (IF-USP)
The large-scale clustering properties of galaxies allow us to investigate models which attempt to explain the recent acceleration of the Universe background expansion. These properties include the correlations of galaxies and the abundance of galaxy clusters. After reviewing some basic cosmological facts, I will discuss the formalism to use the angular correlation function (ACF) of galaxies as well as the cluster abundance (CA) to constrain cosmological models, emphasizing the main problems that need to be accounted for. For the ACF the effects that need to be modeled include redshift distortions, non-linearities, galaxy bias, photometric redshift errors, masks and selection function, etc. For the CA, these effects include mainly the mass-observable relation and its scatter, as well as the completeness and purity of the sample, associated to the optical cluster finder algorithm used. Finally I will present some of our recent results based on Markov Chain Monte Carlo (MCMC) for the ACF analysis applied on real data from the Sloan Digital Sky Survey DR8 and on mock catalogs of the Dark Energy Survey (DES). I will also present MCMC results on the CA analysis for simulations of the DES and prospects for applying these methods on upcoming real data from different surveys, such as the DES and the CFHTLS.
Dark degeneracy and observational tests of interacting models
S. Carneiro (IF-UFBA), H. A. Borges1 & C. Pigozzo
We show that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter w = ˗1. It is also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. We test the interacting dark fluid against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. The model parameters to be adjusted are the present Hubble parameter, the present matter density and a constant parameter athat characterises the interaction. The joint analysis best fit gives a » ˗ 0:5, which corresponds to a constant-rate energy flux from dark energy to dark matter, with the dark energy density decaying linearly with the Hubble parameter. The LCDM model, equivalent to a= 0, stands outside the 3σ confidence interval.
A Brief History of Gastrophysics and Star Formation
Thiago Signorini Gonçalves (Observatório do Valongo, UFRJ)
How are stars formed in galaxies? We know stars originate from the collapse of gas clouds, but recent observations in the distant universe challenge our classical understanding of the physical processes in play in the interstellar medium. Galaxies in the early universe were much denser, and gas was used much more efficiently than in typical spirals in the local universe. In this talk I will discuss recent observations and technical advances — such as the advent of ALMA — that are revolutionizing our understanding of star formation in galaxies and the evolution of properties of the interstellar medium throughout cosmic time.
Probing the Slow-Roll Approximation in Single-Field Inflation with the Planck data
Vinicius Miranda (U. Chicago)
The existence of a quasi-deSitter expansion in the early universe, known as inflation, generates the seeds of large-scale structures and is one of the foundations of the standard cosmological model. The main observational predictions of inflation include the existence of a nearly scale-invariant primordial power spectrum that is imprinted on the cosmic microwave background (CMB), that has been corroborated with remarkable precision in recent years. Generalizations of the vanilla single-field slow-roll inflation provide a wealth of observational signatures in the power spectrum and the non-Gaussianity of fluctuations of the CMB, and this motivates a technique that can evaluate predictions of inflation beyond the slow-roll approximation called the generalized slow-roll (GSR). I will describe the latest searches for signatures of slow-roll violations in the Planck data using the GSR formalism, which is an ideal framework to probe inflationary models in this regime.
Fourier analysis of multi-tracer cosmological surveys
L. Raul Abramo (IFUSP), Lucas F. Secco & Arthur M. Loureiro
We present the optimal quadratic estimators for the Fourier analysis of multi-tracer cosmological surveys. Our estimators can be used to fit simultaneously the matter power spectrum and the biases of the different tracers, redshift-space distortions (RSDs), as well as effects such as non-Gaussianities (NGs). Our estimator reduces to the one by Feldman, Kaiser \& Peacock (ApJ 1994) in the case of a survey consisting of a single species of tracer. We show that the multi-tracer estimators are unbiased, and that their covariance is given by the inverse of the multi-tracer Fisher matrix (Abramo, MNRAS 2013; Abramo & Leonard, MNRAS 2013). When the biases, RSDs and NGs are fixed to their fiducial values, and one is only interested in measuring the underlying real-space matter power spectrum, our estimator is projected into the estimator found by Percival, Verde \& Peacock (MNRAS 2003). We have tested our estimator on simple (lognormal) simulated galaxy maps, and we show that it performs as expected.
Modelos de ricochete com poeira e radiação
Nelson Pinto Neto (Centro Brasileiro de Pesquisas Físicas)
Apresentarei um modelo de ricochete dominado por poeira e radiação onde as perturbações de entropia são naturalmente desprezíveis e o índice espectral pode adquirir uma leve inclinação para o vermelho devido à presença da radiação.
Structure and dynamics of the supercluster of galaxies SC0028-0005
Laerte Sodré (IAG-USP)
According to the standard cosmological scenario, superclusters are objects that have just passed the turn around point and are collapsing. The dynamics of very few superclusters have been analysed up to now. We will present a study of the supercluster SC0028-0005, at redshift 0.22, by identifying the groups and/or clusters that make it up and investigating its dynamical state. For the membership identification, we have used photometric and spectroscopic data from SDSS-DR10. We found 6 bound structures in a flat spatial distribution. We have also used a deep multi-band observation with MegaCam/CFHT to estimate de mass distribution using the weak-lensing effect. For the dynamical analysis, we have determined the relative distances along the line of sight within the supercluster using the Fundamental Plane of early-type galaxies and we have computed the peculiar velocities of each bound structure. The 3D distribution suggests that SC0028-005 is indeed a collapsing supercluster, supporting the scenario of formation of these structures. Using the spherical collapse model, we have estimated the supercluster mass and verified that most of the matter is in the form of galaxy groups or even smaller structures.
Gravity-induced vacuum dominance: an overview
Daniel Vanzella (USP)
In this talk we present an overview of the vacuum-awakening effect by which initially negligible vacuum fluctuations (and energy density) are exponentially amplified by the background spacetime. We also discuss briefly the broader context of gravity-induced instabilities in which the vacuum-awakening mechanism is inserted.
CCDM versus ΛCDM
José Ademir Sales de Lima (IAG-USP)
A short overview of a cosmic accelerating model driven by the negative pressure associated to the gravitationally induced particle production mechanism is presented. The CCDM cosmology can be formulated based on the relativistic irreversible thermodynamics, as well as in a kinetic theoretic approach by incorporating the particle production process. This kind of model has only one free parameter (the creation rate) and the equation of motion is exactly the same of the LCDM cosmology so that the models are dynamically indistinguishable both at the background and perturbative levels. Some possible ways to break such a degeneracy are discussed.
Looking for systematics in the 2-point angular correlation function of galaxies
Armando Bernui (ON)
It is well-known that the BAO phenomenon reveals as a bump in the 2-point angular correlation function (2PACF) of galaxies, considering data in a given redshift shell. However, literature is plagued of 2PACFs where false bumps appears, hiding or making difficult the determination of the BAO-bump angular scale. We perform a surgical approach to analyse these false bumps. Their identification (and possible remotion) helps to get a clear BAO-bump signal, which in turn implies in a best fit of the expected curve, determining with a better precision the angular scale where it appears.
Scalar-Tensor theories and Renormalization Group effects in gravity
Davi Rodrigues (UFES), Bertrand Chauvineau & Oliver Piattella
We show that Renormalization Group modifications of the Einstein-Hilbert action for large scale physics are not, in general, a particular case of standard Scalar-Tensor (ST) gravity. We present a new class of ST actions, which are part of a more general ST picture in which the potential is not fixed at the action level, and show that this extended ST approach formally contains the Renormalization Group case.
Combining cluster counts and galaxy clustering probes
Fabien Lacasa (IFT-UNESP)
Thanks to its 5-year observation of the southern sky (2014-2019), the Dark Energy Survey will enable unprecedented studies of galaxy clustering and cluster constraints on cosmology. I will show ongoing work to combine these two probes to constrain vanilla cosmology and dark energy. The halo model can be used to model the cross covariance between cluster counts and galaxy power spectrum (or real-space correlation function), and I will introduce a diagrammatic method to compute easily the different terms implied and have a simple representation. I will show the importance of using a non-linear model for predictions, and that the cross-covariance is particularly important at low redshifts. A Fisher analysis will prove the nice complementarity and synergy of the two probes for cosmological parameters. Finally I will show how the Gram-Charlier series can be used to compute the joint likelihood of cluster counts and galaxy power spectrum. This likelihood can be highly non-Gaussian due to the Poissonian character of cluster counts, and shall be used in future for realistic forecasts and application to DES data.
Determination of the expansion rate from type Ia Supernovae: a model-independent approach
Sandra Benitez-Herrera (IF/UFRJ)
This work presents a model-independent approach to reconstruct the expansion history of the Universe. Based on large samples of type Ia Supernova (SNe Ia) distance data, it provides constraints on the Hubble parameter without making any hypothesis about cosmological model. The performance of the method is demonstrated through application to simulated data generated in several cosmological scenarios and different calibration frameworks. The method is in closer agreement with the recent Planck-Satellite results than other SN studies. This might be an indication that, in order to tackle subtle deviations from the standard cosmological model present in SN data, it is important to go beyond parametrized approaches and consider non-parametric techniques.
Lensing of point sources
Valerio Marra (UFES)
I will discuss cosmological gravitational lensing of point sources by matter structures along the line of sight. I will examine weak gravitational lensing of standard candles, in particular the cosmological information which can be extracted from lensing of supernovae Ia. I will then consider strong gravitational lensing of quasars, whose double images are forecasted to be observed by several future surveys. Quasar lensing is expected to provide valuable cosmological and astrophysical information.