Panel

Close

Member Panel

Logout

Internal Documentation

Talks

Ana Afonso

Saving Mankind by looking for wondering stars

Abstract: I have participated in the discovery of three Near-Earth Asteroids (NEAs) as part of my observing duties as astronomer at Isaac Newton Telescope (INT) last December and in contribution to the European Near Earth Asteroids Research (EURONEAR) project. The EURONEAR is a project tailed to discover and track NEAs and Potentially Hazardous Asteroids (PAHs) using a network of 20 sub-meter to 4 meter telescopes spreaded over 5 countries. PHAs are the NEAs having a Minimum Orbital Intersection Distance less than 0.05 AU sizes larger than 150 m. This size limit selects objects which can potentially cause a global climate disaster and threaten the survival of mankind. Here I plan to introduce the importance of such programs in the context of understanding our solar system to a greater detail and to the security of mankind as a whole by discovering and tracking possible impactors.

José Afonso, Jordi Casanellas and Hugo Messias

Towards the first generation of Radio Powerful AGN in the Universe

Abstract: The existence of powerful AGN has now been established well within the first Gyr of the Universe, through the observations of tens of QSOs up to the currently highest redshift of z~7 and theoretical work that shows how such super-massive (M~10^9 Msun) black holes can exist at such early epochs. In particular, these results imply that radio powerful sources should exist at very high redshifts (z > 7), even if all efforts to detect them have so far been unsuccessful. Over the coming years, powerful new facilities like the JVLA, GMRT, LOFAR, and the several upcoming SKA pathfinders experiments (ASKAP, MeerKAT, WSRT-Apertif) will dramatically increase our knowledge of the Radio Universe. Revolutionary deep-wide radio surveys like EMU, WODAN, or LOFAR will cover the sky at extreme depths over unprecedented large areas, and the first radio galaxies of the Universe should be finally identified. In this talk I will discuss our efforts to identify the earliest radio monsters of the Universe, and how the upcoming generation of full-sky deep radio surveys will lead to the discovery of the first radio galaxies, overcoming the limitations found in the deepest radio observations currently available.

Paulo Andrade, Johan Kolb, Inês Carvalho and Paulo Garcia

Correcting cross-coupling and aliasing effects in the estimation of atmospheric turbulence parametes from Shack-Hartmann wavefront data

Abstract: The method of Zernike decomposition of the wavefront phase for the estimation of atmospheric turbulence parameters from the telemetry data of an Adaptive Optics system is revisited. Using simulated data modeling the Shack-Hartmann wavefront sensor from the Nasmyth Adaptive Optics System of the Very Large Telescope, the effects of cross-coupling and aliasing are analyzed. The impact of these effects on the modal variances for each reconstructed mode and its dependence on the truncation of the reconstructors is studied for least squares reconstructors, as well as the optimal number of modes that should be used in the estimation of the Fried parameter, r0, and the outer scale of turbulence, L0. An algorithm is proposed to improve the accuracy of the estimates by correcting for cross-coupling and aliasing the variances of the reconstructed coefficients. Simulations show that the bias in the estimations of the turbulence parameters due to cross-coupling and aliasing is removed allowing for relative uncertainties lower than 1% for the r0 estimation and lower than 6% for the L0 estimation.

Pedro Aniceto

Thin shell collapse and Cosmic Censorship with charged black holes in string theory

Abstract: In general relativity, any curvature singularities that develop from evolving generic and regular initial data should be hidden behind event horizons. This is the statement of the (weak) cosmic censorship conjecture, whose proof remains elusive after more than 40 years. When applied to gravitational collapse of matter, the conjecture suggests that singularities can form when covered by black hole horizons, but naked singularities can never arise. This picture was confirmed by Boulware in 1973 in the context of Einstein-Maxwell theory, where he considered the spherical collapse of charged thin shells of matter. In this work we are interested in testing the possibility of formation of naked singularities in a modified theory of gravity, corresponding to four-dimensional low-energy string theory. The theory is based on the addition of a scalar field (the dilaton) to the metric and Maxwell field. The presence of the dilaton may reduce the critical value of the electric charge necessary for the appearance of a naked singularity. We investigate the dynamics of charged thin spherical shells in this Einstein-Maxwell-dilaton theory and compare it with Boulware's study. Moreover, we find conditions on the mass and charges of the shell that lead to collapse from infinity and obey reasonable energy conditions. This provides a window into cosmic censorship in alternative theories of gravity as well as a test of the viability of string-inspired models.

Joana Ascenso

PSF reconstruction for enhanced data processing tools

Abstract: Existing tools to extract accurate photometry and astrometry from adaptive-optics images currently hinge on the presence of bright, isolated stars in the image from which to create a reliable model of the peculiar AO point spread function. For many science cases these stars are often missing, leaving the task of PSF-fitting very poorly constrained. I will review the existing methods for PSF photometry, their limitations for AO-assisted images, and present the preliminary results of a systematic study with synthetic (GL)AO data to assess the improvements of adding information about the PSF from the AO telemetry and PSF reconstruction algorithms to the PSF-fitting post-processing tools.

Bruno Barros and Nelson Nunes

3-form inflation in a 5D braneworld

Abstract: It has been shown that 3-forms present viable cosmological solutions for inflation and dark energy. In this talk, I will present the dynamics of a single 3-form in the Randall-Sundrum II scenario, where the 3-form is confined to the brane, and find an inflationary solution for some suitable choices of the potential. I will focus on the influence of the fifth dimension (bulk) on the dynamics of the brane in comparison with the 4-dim case already studied. Finally I present the scalar and tensor power spectra for the presented model.

Iris Breda, Polychronis Papaderos and Jean Michel Gomes

A spatially resolved exploration of the nature and assembly history of pseudo-bulges in the CALIFA galaxy survey

Abstract: The understanding of the nature and formation history of galaxy pseudo-bulges is fundamental to the development of a comprehensive evolutionary picture for Hubble-type galaxies and their structural components. These entities, bridging the morphological gap between a virtually absent stellar spheroid in the centers of bulgeless disks and a prominent classical bulge in S0 galaxies, are, according to our current understanding, assembling gradually in the course of secular galaxy evolution through low-level star formation, fed by inflowing gas from the disk and/or disk instabilities. If so, pseudo-bulges are expected to markedly differ from the quasi-monolithically formed classical bulges in their star formation history and chemical abundance patterns. To test this simple expectation, and gain further insight into the evolutionary pathways of pseudo-bulges we are carrying out a structural and spatially resolved spectral synthesis study of pseudo-bulge galaxies from the Calar Alto Legacy Integral Field spectroscopy Area survey (CALIFA; http://califa.caha.es). Preliminary results from this study will be presented.

Fernando Buitrago

Scientific volunteering in East Africa: Opportunities in Astronomy

Abstract: The East African Astronomical Society (EAAS) is an organisation formed in 2010 by Burundi, Rwanda, Uganda, Tanzania, Kenya, Sudan and Ethiopia intended for promoting both professional Astronomy as well as public understanding of Astronomy in the region. I will introduce in this presentation some of the projects we are conducting at the moment, such as the MSc in Astronomy and our facilities, among which the new Entoto Observatory stands out. It is composed of two twin 1m telescopes that are in the commissioning period at the time being. EAAS counts with a strong support from the IAU and the Office of Astronomy for Development, and due to its quick growth, offers the possibility to external researchers and engineers to come to a number of its centres for teaching and scientific volunteering purposes. I will review the month and a half I spent in Uganda (Mbarara University for Science and Technology) and Ethiopia (Addis Ababa University/Entoto Observatory), highlighting the possibilities for improving high-level education in the East Africa and obtaining well trained and very enthusiastic master and PhD students.

João Calhau and David Sobral

The growth of typical star-forming galaxies and their super massive black holes across cosmic time

Abstract: Understanding galaxy formation and evolution requires the understanding of both the star formation history (the growth of galaxies) and black hole accretion history (the growth of their black hole), and how they influence each other. Here, we explore a sample of typical Halpha-selected star-forming galaxies from the HiZELS survey.We use direct detections but also relying on stacking in the X-rays, far-infrared (FIR) and radio, along with the wealth of multiwavelength data in COSMOS to study the relative growth between typical galaxies, from z=2.23 to z=0.4, and their black holes. We find that the fraction of AGN increases with Halpha luminosity and that the relative black hole to galaxy growth seems to be relatively constant for star forming galaxies since z=2.23. We find a typical fraction of AGN candidates of 20%, although only about 1% were selected through the X-rays. Typical Star Forming galaxies are shown to grow their stellar mass much quicker than their black holes (ratio of -4 dex) with SFR’s of the order of 10 to 100 solar masses per year and an AGN accretion rate of the order of 10^3 Msolar/yr. Our results may have important consequences for our understanding of how galaxies like our own evolved in the last 11 Gyrs.

Rosetta: Mission Accomplished

Abstract: In 2014, for the first time in history, a spacecraft orbited and landed on a comet’s surface. This extraordinary mission had its beginning over 20 years ago, when the European Space Agency started its preparations, involving dozens of scientists and engineers from different countries and space agencies. Rosetta, who was launched in 2004, has travelled a distance over 3 times the distance between the Earth and the Sun, to reach Comet 67P/Churyumov–Gerasimenko and help decipher the origins of life in the Solar System. How can we communicate to the public the importance of this historic event that is happening so far away? How can we demonstrate the importance of the investment in Space Science to the improvement of the conditions of life on Earth? The Rosetta mission will be used as an example of success of science communication and public engagement with space technology and science. We will present the highlights of the Rosetta outreach campaign and its impact evaluation.

Alexandre Correia, Adrien Leleu and Philippe Robutel

Spin-orbit coupling and chaotic rotation for the small moons of Pluto

Abstract: Circumbinary bodies are objects that orbit around a more massive binary system. Here we show that, contrarily to the classical two-body problem, circumbinary bodies in planar quasi-circular orbits can present stable non-synchronous rotation. Denoting nb and n the orbital mean motion of the binary and of the circumbinary body, respectively, there is an entirely new family of spin-orbit resonances at the frequencies n +/- k v / 2, where v = nb - n, and k is an integer. In addition, when the natural rotational libration frequency has the same magnitude as v, the individual resonances overlap and the rotation becomes chaotic. We apply these results to the small moons in the Pluto-Charon system.

Rui Curado Da Silva and Jorge Maia

XIPE: the X-ray imaging polarimetry explorer

Abstract: Last June 4th, ESA selected to phase S three candidate concepts submitted to its ‘M4’ mission call. Among this mission concepts is XIPE (the X-ray imaging polarimetry explorer: http://www.iaps.inaf.it/xipe/index.htm). X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2–10 keV band in 105 s for pointed observations, and 0.6 % for an X10 class solar flare in the 15–35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin × 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 μs. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut f¨ur extraterrestrische Physik. LIP Coimbra group will contribute to the optimization of the gaseous mixture of the main instrument detectors, the GPDs.

Cosmic Rays Anisotropies and Point Sources at Pierre Auger Observatory

Abstract: The Pierre Auger Observatory is an hybrid detector covering an area of 3000 km^2 and capable of studying the ultra-high-energy cosmic ray (UHECR) around 10^18 to 10^20 eV. It is the best detector to observe the UHECR sources on the Southern hemisphere. The distribution of arrival directions studies, of ultra-high-energy cosmic rays at the Observatory includes arrival directions with zenith angles up to 80º and covering -90º to +45º in declination. Several tests were performed, such as correlations with active galactic nuclei from VCV catalog, blind searches for localized excess fluxes and for self-clustering of arrival directions. None of the searches show a statistically significant evidence of anisotropy. The largest departures from isotropy were obtained around Swift-BAT AGNs closer than 130Mpc and around Centaurus A, with 1.4% probability to appear from an isotropic distribution. The study of spherical harmonic moments are well-suited to understand the anisotropy at any scale. A full-sky coverage, combining both northern and southern hemispheres, allows to unambiguously measure the full set of spherical harmonic coefficients. The joint analysis at the Telescope Array and the Pierre Auger Observatory give the opportunity to do anisotropy searches with the multipolar expansion of the cosmic ray fluxes with no significant deviation from isotropic expectations. Upper limits on the amplitudes of the dipole and quadrupole moments are derived as a function of the sky direction, varying between 7% and 13% for the dipole and 7% to 10% for a symmetric quadrupole. The results on the photon and neutrinos studies are reviewed. No neutrino candidate was detected, yielding a limit to the diffuse flux of ultrahigh energy neutrinos that challenges the Waxman-Bahcall bound predictions. No photon point source were found and upper limits have been derived, in mean value and for every direction in the sky. Both photons and neutrons fluxes significantly constrain models of EeV protons emitted by non-transient sources in the Galaxy.

Joao Ferreira, James Dunlop and Vivienne Wild

Emission Line Galaxies in CANDELS I: H-alpha, [OIII] and [OII] Equivalent Width Distributions from Panchromatic Broadband Photometry from z=0.1 to z=5

Abstract: Concerted efforts in high-z galaxy evolution in recent years have formed a consistent picture of rising star formation, peaking at z=2 that exponentially decreases until today. Yet, the details of how this transition from a gas-rich, bursty universe to today's quiescent one needs an explanation, especially in the light of the evidence for a main sequence of star formation and different feedback properties of galaxies below and above the knee of the mass function. A better understanding of galaxy formation needs large samples of objects down to the masses of dwarf galaxies: Using a combination of the wealth of deep (H<26) CANDELS broadbands in visible and NIR bands and a set of line-free stochastic burst models based on BC03 we extend standard colour-colour selection methods to select strong (EW>200A) emission-line galaxies (ELGs) in [OII], [OIII] and H-alpha and estimate equivalent widths (EWs) to produce ELG EW distributions over 0.3mass/M_sun>10^9 for all these lines. These distributions display long tails of extreme equivalent widths and, more surprisingly, very high fractions (up to 30%) of ELGs in the described mass range. While [OIII] and H-alpha fractions both increase from z=0.3 to z=2, [OII] does not follow this increase, which indicates that a transition in [OIII]/[OII] and ionization parameter is at work at z=2 for these objects.

Miguel Ferreira and Carlos Martins

Consistency tests of the stability of fundamental couplings

Abstract: We analyse the consistency of current astrophysical tests of the stability of the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $\mu = m_p/m_e$ with combined measurements of $\alpha$, $\mu$ and the proton gyromagnetic ratio $g_p$. We find that apparent inconsistencies, at about the two-sigma level, persist and are in some cases enhanced, especially for matter era measurements (corresponding to redshifts $z>1$). Although hidden systematics may be the more plausible explanation, we briefly highlight the importance of clarifying this issue, which is within the reach of state-of-the-art observational facilities such as ALMA and ESPRESSO.

Jean Michel Gomes, Polychronis Papaderos, Carolina Kehrig, José Manuel Vílchez, Iris Breda, Bodo Ziegler and Sebastian Sánchez

Extended nebular emission and gas excitation mechanisms in early-type galaxies from the CALIFA galaxy survey

Abstract: The morphological, spectroscopic and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational insights into the ionization mechanisms and the buildup history of these massive, quiescent systems. High-quality IFU data with a wide spectral and spatial coverage (e.g. CALIFA survey - http://califa.caha.es), offers an unprecedented opportunity for advancing our understanding in this respect. We present a spatially resolved 2D investigation of 32 ETGs from CALIFA, based on Hα intensity and equivalent width (EW) radial profiles and maps, diagnostic emission-line ratios, and ionized-gas and stellar kinematics. The combined interpretation of these data is supported by evolutionary and photoionization models allowing to quantify the relative contribution of an AGN, diffuse low-level SF and post-AGB stars to the excitation of the wim in different radial zones. We find that these systems span a broad, continuous sequence in the properties of their wim, exemplified by two distinct classes. The first one (type i) are systems with a nearly constant EW in their extranuclear emission, in quantitative agreement with (even though, no proof for) the pAGB hypothesis as the main driver of extended wim emission. A subset of these ETGs (type i+) exhibit low-level SF activity in its extreme periphery, as reflected upon emission-line EWs rising up to ~20 Å in their outskirts. The second class (type ii) stands for virtually gas-evacuated ETGs with a very low (<0.5 Å), outwardly increasing EW. These two classes appear indistinguishable from one another by their LINER-specific emission-line ratios in their nuclear and extranuclear component. Additionally, our analysis further highlights the diversity of ETGs with respect to their gaseous and stellar kinematics. Whereas, in one half of our sample, gas and stars show similar (yet not identical) velocity patterns, both dominated by rotation along the major axis, our analysis also documents several cases of kinematical decoupling between gas and stars, or rotation along the minor axis. We show that the generally very low (~1 Å) EWs in ETGs make necessary a careful quantitative assessment of potential observational and analysis biases in studies of their wim. We demonstrate that, at the typical emission-line detection threshold of ~2 Å, most of the extranuclear wim emission in an ETG may evade detection, which could in turn prompt its classification as an entirely gas-devoid system.

Morgan Le Delliou

Method of detection of Dark Energy-Dark Matter interaction in Non-virialised clusters

Abstract: We investigate the possibility to evaluate the departure from virial equilibrium of unbalanced clusters in order to detect, in that balance, effects from a Dark matter–Dark energy interaction. We extend the use, from previous works, of the Layzer–Irvine equation for dynamical virial evolution of a simple model of interacting dark sector, with weak lensing and X-ray observations giving respectively the mass profiles and the intracluster gas temperatures. Selecting a set of clusters, we generate measurements, through a Monte Carlo method, of observed virial ratios, interaction strength, rest virial ratio and departure from equilibrium factors. We found a compounded interaction strength for the set of clusters of $−1.61^+2.23_−16.34$, compatible with no interaction, but a compounded rest virial ratio of $−0.78 ± 0.13$, which would entail a 2σ detection. We confirm quantitatively that clusters of galaxies are out of equilibrium but further investigation is needed to constrain a possible interaction in the dark sector.

Ana Catarina Leite

Optimization of ESPRESSO Fundamental Physics Tests

Abstract: ESPRESSO is a high-resolution-ultra-stable spectrograph for the VLT, whose commissioning is expected in late 2016. One of its key science drivers is to test the stability of fundamental couplings such as the fine structure constant with unprecedent accuracy and control of possible systematics. I will describe the criteria for selecting an optimal target list for the Consortium's GTO and present forecasts of the impact that this sample will have on fundamental physics and cosmology. In particular, I will discuss how these measurements will constrain the behavior of dark energy deep in the matter era (i.e., in the redshift range 1.5

José P. S. Lemos and Vilton T. Zanchin

Sharp bounds on the radius of relativistic charged spheres: Guilfoyle's stars saturate the Buchdahl-Andreasson bound

Abstract: Buchdahl, by imposing a few reasonable physical assumptions on the matter, i.e., its density is a nonincreasing function of the radius and the fluid is a perfect fluid, and on the configuration, such as the exterior is the Schwarzschild solution, found that the radius r_0 to mass m ratio of a star would obey the bound r_0/m > 9/4, the Buchdahl bound. He also noted that the bound was saturated by the infinite central pressure Schwarzschild interior solution, i.e., the solution with rho_m(r)=constant, where rho_m(r) is the energy density of the matter at r. Generalizations of this bound in various forms have been studied. An important generalization was given by Andreasson by including electrically charged matter and imposing a different set of conditions, namely, p+2p_T < rho_m, where p is the radial pressure and p_T the tangential pressure. His bound is sharp and is given by r_0/m > 9/[1+ sqrt(1+3q²/r_0²)]², the Buchdahl-Andreasson bound, with q being the total electric charge of the star. For q = 0 one recovers the Buchdahl bound. However, following Andreasson's proof, the configuration that saturates the Buchdahl bound is an uncharged shell, rather than the Schwarzschild interior solution. By extension, the configurations that saturate the electrically charged Buchdahl-Andreasson bound are charged shells. One could expect then, in turn, that there should exist an electrically charged equivalent to the interior Schwarzschild limit. We find here that this equivalent is provided by the equation rho_m(r) + Q²(r)/(8 pi r⁴) = constant, where Q(r) is t he electric charge at r. This equation was put forward by Cooperstock and de la Cruz, and Florides, and realized in Guilfoyle's stars. When the central pressure goes to infinity Guilfoyle's stars are configurations that also saturate the Buchdahl-Andreasson bound. It remains to find a proof in Buchdahl's manner such that these configurations are the limiting configurations of the bound.

Silvio Lorenzoni

Lyman-break galaxies in the Epoch of Reionization

Abstract: I will present a selection of robust Lyman-break galaxy candidates at redshifts z ∼ 6 − 10, within the Epoch of Reionization, from the latest available ground- and space-based datasets. This sample shows significant and rapid evolution of the galaxies’ properties and of their luminosity function with redshift. The star formation history in this time frame and its implications for reionization will also be discussed.

Paulo Luz and José P.S. Lemos

Static Electrically Charged Star Shells: Normal and Tension Shells

Abstract: The junction of an interior Minkowski with an exterior Reissner-Nordström spacetime is studied. Using the Israel junction formalism a perfect fluid static thin shell separating an interior Minkowski outside Reissner-Nordström spacetime is considered. Defining the Kruskal-Szekeres coordinates for the maximally extended Reissner-Nordström spacetime, the presence of a thin shell at any allowable sub-region is analyzed and the properties of the shell, the energy density and the pressure, are studied. The cases of pressure and tension static shells of matter appear naturally depending on the sub-region where the shell is considered. The energy conditions verified by a thin shell, for all the possible cases, are analyzed.

Carlos Martins

Fundamental cosmology in the ESPRESSO and Euclid era

Abstract: I will describe how the combination of various astrophysical datasets can constrain fundamental cosmology, and briefly highlight current constraints. In particular I will show how the combination of current tests of the stability of fundamental couplings and supernova and BAO data lead to indirect constraints on the Eotvos parameter (quantifying possible Weak Equivalence Principle violations) that are one order of magnitude stronger than the direct ones (obtained from torsion balance and lunar laser ranging experiments). Finally I will present forecasts quantifying the improvements that may be expected once data from the ESPRESSO spectrograph and the Euclid satellite is available.

Hugo Martins and David Sobral

The role of the environment in the star formation of galaxies in 3 X-RAY clusters at z ~ 0.86 in the COSMOS field

Abstract: One of the most fundamental aims of extragalactic astrophysics is to understand how galaxies form and evolve across cosmic time. Being this evolution strongly affected by the galaxies internal dynamics, it is very important to study how galaxies form stars and what mechanisms affect the star formation. It has been shown that the environment in which this galaxies live has a very important role on the star formation of such galaxies. Normally, young and massive stars live in cloudy environments which are photo-ionized by the radiation of such stars. By studying the Hα emission line (which is a very solid tracer of star formation), we can trace if such clouds are indeed forming stars. However, when studying galaxies at more than z ~ 0.3, H-alpha becomes redshifted to the near infrared, in which there is a real challenge for ground based observations because of the atmosphere emission lines. Fortunately, this is a problem that we can overcome by studying the OII emission line, since the UV emission of these young populations of stars is strong enough to ionize heavier elements such as neutral oxygen. After understanding if the galaxies in which these clouds are embedded are actively forming stars, we can find what is the correlation between the activity of these galaxies and the environment they live in. In this work, we look at the OII emission lines of ~ 1000 galaxies at z ~ 0.86 in 3 X-RAY clusters in the COSMOS field by individually confirming the OII emission line with high-resolution spectroscopic data from the VIMOS instrument at the VLT. With this information we can find how strongly the star formation depends on the environment and compare these results with previous star formation/environment correlations.

Hugo Messias, Neil Nagar, Franz Bauer and José Manuel Afonso

The Universe through lenses

Abstract: Like the way one uses magnifying lenses to improve the view of the very small Universe, massive gravitational potentials can help astronomers to reach out the very far Universe. This presentation will report on the latest developments on two Chilean-led projects I am involved targeting strong-lensing cases making use of data obtained with the Atacama Large Millimeter Array (ALMA). One of the projects, covers three known lensing galaxy clusters (A2744, MACS0416, and MACS1149) at millimeter wavelengths as a means to assess the dust and gas contents of background magnified galaxies or to blindly search for optically-undetected dusty high-redshift galaxies. The other project focus on one galaxy-galaxy lensing system (HATLAS J142935.3-002836, aka, H1429-0028), where the background galaxy is found to be a ~1:3 gas-rich starburst merger at z=1.027 (Messias et al. 2014, Timmons et al. 2015). I will also take the chance to report on the user support provided by the Portuguese ALMA Centre of Expertise during Cycle-3 and its national and international outcome statistics.

José Pedro Mimoso, Francisco S. N. Lobo and Salvatore Capozziello

Generalized energy conditions in Extended Gravity re-examined: the modified Gauss-Bonnet theory case study.

Abstract: We consider Extended Theories of Gravity (ETG) and in particular Modified Gauss-Bonnet theory. These theories involve further degrees of freedom related to curvature invariants, and scalar fields that can be recast as effective fluids, which differ in nature with respect to the standard matter fluids. It is thus somewhat misleading to apply the standard general relativistic energy conditions to the corresponding effective energy-momentum tensor, as the latter contains the matter content and geometrical quantities. We explore this subtlety in cases with generalized explicit curvature-matter couplings, which imply the non-conservation of the energy-momentum tensor. Thus, in the context of ETGs, interesting results appear such as matter that may exhibit unusual thermodynamical features, for instance, gravity that retains its attractive character in the presence of large negative pressures; or alternatively, we verify that repulsive gravity may occur for standard matter. Refs: Phys.Lett. B730 (2014) 280-283; Phys.Rev. D91 (2015) 12, 124019.

Filipe Monteiro and José P.S. Lemos

Shapiro delay in d->Infinity Dimensions

Abstract: Classical General Relativity in more than four spacetime dimensions has been the subject of increasing attention in recent years. GR simplifies dramatically in the limit of large dimensions since it reduces to a theory of non-interacting particles, of finite radius but vanishingly small cross sections, which do not emit nor absorb radiation of any finite frequency. Since in this limit its dynamics become trivial we have a strong motivation for the study of the theory in an 1/d expansion. In this oral communication we'll review orbit solutions in higher-dimensional vacuum gravity. We'll discuss the Shapiro delay effect for a photon orbit and derive its large d-dimensional expression. It is also shown through explicit examples that this large-d expansion can be a very efficient method for analytic calculations, achieving surprisingly accurate results even for relatively low dimensions

João Morais, Mariam Bouhmadi-López and Salvatore Capozziello

Dark Radiation in f(R)-gravity: the portrait of scalar perturbations

Abstract: We address the possibility that a suitable modification of gravity, of the type f(R)-gravity, could account to some amount of the radiation we observe today, in addition to the possibility of explaining the present speed up of the universe. The effects of the f(R)-gravity at the perturbative level are obtained by evolving the scalar perturbations since deep in the radiation epoch, when the modes are outside the horizon, until the present time. In particular, we look for signatures in the matter power spectrum as would be measured today.

Cosmology of the de Sitter Horndeski models

Abstract: Horndeski models with a de Sitter critical point for any kind of material content can provide a mechanism to alleviate the cosmological constant problem. We study the cosmological evolution of two classes of families - the linear models and the non-linear models with shift symmetry. We conclude that the latter models can deliver a background dynamics compactible with the latest observational data.

Joana Oliveira, Hugo Messias, Bahram Mobasher and José Afonso

Comparing the hot- and cold-dust contribution in galaxies and its evolution in the last 10 Gyr

Abstract: We study the contribution of hot- (880 K) and cold-dust (10-50 K) to the luminosity density of galaxies and its evolution with cosmic time. Using the Spitzer-IRAC data and the Herschel Multi-tiered Extragalactic Survey (HerMES) and PACS Evolutionary Probe (PEP) data over an area of 1.8 square degrees covered by the COSMOS field, we estimate the contribution from hot-dust at rest-frame 3.3 um and the contribution from cold-dust at far infrared wavelengths (from 0 < z < 0.2 up to 0.9 < z < 1.9) to obtain a relation between both. The contribution due to stellar emission is estimated from the rest-frame 1.6 um luminosity (assumed to result from stellar emission alone) and, taking advantage of the age-independent shape of the 1.6-4.2 um stellar continuum, subtracted from the mid-infrared luminosity of galaxies to measure hot-dust emission. The contribution from cold-dust is characterized by performing a stack analysis of the 100-500 um data, using a weighted median, and a modified black-body spectral fit analysis to the stacked data points. This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected active galactic nuclei. The results to be presented are the continuation of the work shown in Messias et al.(2013), and are part of an on-going master-thesis work.

Ciro Pappalardo

Physical properties of a population of low Far Infrared luminosity galaxies at z < 1

Abstract: Using deep Herschel data on behalf of the Herschel Virgo Cluster Survey, we investigate the physical properties of a sample of nearby galaxies (z<0.6) in the background of the Virgo cluster. Galaxies are selected at 250 micron and are complemented with a set of multi wavelengths data covering the Spectral Energy Distribution (SED) from Ultra Violet (0.15 micron) to the Far Infra Red (500 micron) wavelengths. The SEDs have been analysed using two different statistical methods, MAGPHYS and CIGALE, allowing a valid cross check of the robustness of our conclusions. Our galaxies have in average a low star formation rate (0.02 < SFR < 70 M_sol/yr), and a low dust luminosity (average L_dust ~ 5+/-2 1e10 L_sol), and represents normal star forming galaxies experiencing the shut down of the star formation observed below z<1. This is clear observing their position in a SFR-Mstars diagram, where they occupy a transition region between local spirals, low redsfhit LIRGs and z>1 ULIRGs. With respect to a similar Herschel survey (H-ATLAS), we found comparable dust masses but lower SFR, implying that despite the presence of dust, our galaxies are in a quenching stage of their evolution. Also a similar analysis using IRAS instrument revealed a less prominent dust component, because of the selection more sensitive to the warm dust. We then used a stacking technique to build a SED template representative of normal star forming galaxies at z<1. Comparisons with previous templates show the importance of MIR data in determining the shape of the SED above 3 micron, above all in the regions where stellar and dust components mix together. This SED can be used as an empirical template to investigate galaxies at higher z, because lower FIR luminosities imply overall colder dust temperatures, a condition that could be found at higher z more frequently than previously thought. Different studies have shown indications for a colder dust temperature in high z sub-mm galaxies with respect to local galaxies with similar FIR luminosities.

Dário Passos

Magnetic forcing of large scale flows in stellar convection zone

Abstract: From an evolutionary point of view, stellar dynamics are well explained using nuclear physics, thermodynamics and simple hydrodynamics. For this reason, over many years, stellar magnetism was relegated to a secondary plane and its effects were considered of negligible for stellar evolution. With the advent of high cadence and high resolution observational data from the Sun and sun-like stars, this perspective has changed over the last two decades. Magnetism is now thought to have a crucial role in some critical phases of stellar evolution, e.g. in the formation of proto-stellar jets, contributing to angular momentum redistribution and structure stability. On the other hand, the evolution of stars over Human time scales (from years to centuries) is mainly controlled by magnetism. The most evident proof of this can be found in the magnetic cycle that our Sun exhibits and that is responsible for solar and geomagnetic storms. The solar magnetic field is produced by a dynamo mechanism that operates in the outer layers of the Sun, the so called convection zone. Until recently it was thought that this magnetic field was a direct product of differential rotation and convective turbulence and that its feedback effects in the stability of the convective zone was negligible. Recently Helioseismology showed that the two main large scale flows in the Sun, differential rotation and meridional circulation, suffer amplitude modulations over the course of the 11 year solar cycle but the physical cause for these variations remained elusive. 3D MHD simulations of solar convection are now starting to provide some answers about how the magnetic field is influencing stellar large scale flows. In this talk I'll present a study based on a global MHD simulation of solar convection that shows that torsional oscillations (variation in the differential rotation) and the amplitude modulation of the meridional flow can be explained by angular momentum transfers mediated by the magnetic field. More specifically we can show that the mechanism of gyroscopic pumping and the magnetic torque associated with the large scale magnetic field contribute to changes in the morphology of the meridional circulation in certain parts of the convection zone. This result, when confirmed by other groups, will have a profound impact in the way current mean-field dynamo models are implemented, i.e. the ubiquitous kinematic regime used can no longer be considered a good approximation to run these models.

Gonçalo Quinta and Antonino Flachi

Vacuum polarization around Lifshitz black holes

Abstract: The vacuum polarization of a scalar field around a Lifshitz black hole geometry is studied using a WKB analytic expansion and a point-splitting regularization. We follow the standard approach, which consists in regularizing the divergences of the Green function using a point-splitting method, subtracting them from the initial expression and finally taking the coincidence limit, thus obtaining a renormalized result. The final expression is naturally expressed in terms of generalized zeta functions. We demonstrate some methods to numerically compute these quantities which are then used to evaluate the vacuum polarization for a massless scalar field in a particular choice of Lifshitz spacetime.

José Ribeiro

Spectrography using Small Telescopes: A recent contributor to stellar astrophysics

Abstract: In an epoch where the largest telescope of the world is in construction, small telescopes are gaining an important role in the optical spectrographic study of bright stars. Indeed, many bright stars lack information, due to the fact that they need long time observing runs which large telescopes cannot assure. Small telescopes need small spectrographs. Their performance rivals in low and medium spectral resolution with the bigger systems, magnitude limits apart. During the CoRoT asteroseismic mission on Be stars, most of the land spectroscopic support was done with small telescopes with good results. During the last three years long term runs on the bright stars of Orion were performed with MOST (and Chandra) and more recently with BRITE constellation. Here too, small spectrographic systems gave the required land support. Since 2006 many other campaigns were organized by using such small systems in long term runs. That's the case of the WR140 periastron in 2009, epsilon Aurigae eclipse in 2010, delta Scorpii periastron in 2011 where a small Littrow was for the first time attached to the IAC80 telescope, more recently WR134, WR135 and WR137 in 2013, V339 Delphini, a nova studied from the very first day with more than one thousand spectra in five months, eta Carina periastron in 2014, only to mention the most important campaigns. Small systems are also feeding the Be star database (BeSS) leaded by the Paris Observatory and accessible through the Virtual Observatory. Alike the AAVSO for photometry, the Astronomical Ring for Access to Spectroscopy (ARAS group) gathers most of the spectrographic observers, and accepts observing campaigns from the community.

Nathan Roche

MUSE 3D Spectroscopy and Kinematics of the Interacting Radio Galaxy PKS 1934-63

Sérgio Santos, David Sobral and Jorryt Matthee

Lyman-alpha emitters at the peak of the star-formation history: implications for the luminosity function across cosmic time

Abstract: Our recent narrow-band studies allowed us to probe by far the largest volumes (~5deg^2) in the distant Universe (when the Universe was less than 1 Gyr old). We have found and confirmed the brightest Lyman-alpha emitters (LAE) at z~7, and showed they are much more common than previously thought. However, current lower redshift surveys simply lack the volume to provide a direct comparison, and thus it is unclear whether the number densities and nature of such sources evolves across cosmic time. In order to overcome the current limitations, we are conducting multiple narrow-band surveys at z<6 which can be directly compared with our z~7 surveys of the very young Universe. Here I will present our first results at redshifts of 2.2 and 3.1, roughly the peak of the star-formation history of the Universe, from our pilot observations over 2-3 deg^2.

Tom Scott, Elias Brinks, Alessandro Boselli, Luca Cortese and Hector Bravo-Alfaro

Evolution of late-type galaxies in Abell 1367: Cold Gas

Abstract: There is evidence linking the galaxy cluster environment to the removal of cold gas from its late-type galaxies, which in turn leads to the quenching of their star formation. At low z the consensus view is that ram pressure stripping is the dominant process driving this gas removal, although this remains controversial. We are undertaking HI and molecular gas studies in the late-type galaxies of the cluster Abell 1367 (z ~0.02), which is undergoing an equal mass merger. Abell 1367’s late-type galaxies display widespread HI and molecular gas signatures, which are inconsistent with current ram pressure stripping models. We are now investigating what mechanisms produce the abnormal HI and molecular gas signatures and whether they are specific to merging clusters in general.

Manuel Silva

PSF reconstruction for the MUSE-GalacsiGLAO mode in Python

Abstract: The resolution of ground-based telescopes can be dramatically increased by using Adaptive Optics (AO) instruments to correct wavefront distortions introduced by Earth's atmosphere. The use of AO systems is growing at an increasing rate and ESO, in particular, is already preparing the next generation of AO instruments for both the VLT and the E-ELT. Even though the corrected images obtained with these instruments are closer to the ultimate diffraction limit, the correction is not perfect, particularly in the case of a large Field of View. Thus, it is often necessary to use a posteriori image processing techniques in order to improve estimation of astrophysical data. These techniques require accurate knowledge of the system's PSF in an arbitrary position in the Field of View. I present a PSF reconstruction software, written in Python, which estimates the PSF in the particular case of the MUSE/GALACSI instrument.

David Sobral

Discovery of PopIII stellar populations in bright galaxies at z~7: paving the way for JWST

Abstract: I will present new results from our very wide Lyman-alpha surveys at multiple cosmic time slices within the first Gyr of cosmic time since the Big Bang. We are leading the largest narrow-band surveys ever conducted with CFHT, Subaru and the INT on multiple fields, to look for luminous Lyman-alpha emitters at z~6-9. Surprisingly, we find a much higher space density of luminous Lyman-alpha emitters at z~6-7 than previously assumed, which we confirm spectroscopically with Keck and the VLT. Our unique samples include sources even more luminous in Lyman-alpha than Himiko at z=6.6, showing that very luminous Lyman-alpha emitters are much more common than thought at z~6.6 and with strong consequences for re-ionisation. Most interestingly, we have found a unique source: CR7, the first distant source discovered with clear evidence of the first, extremely massive, metal free stars. CR7 is most likely powered by a PopIII-like stellar population (very high EW Lyman-alpha, high EW HeII, and no other metal lines) in one of its components which is unveiled by HST/WFC3 (Sobral et al. 2015, arXiv:1504.01734). The alternative explanation is equally exciting, as it would mean that we have found the first direct collapse black hole ever observed.

Posters

Ana Afonso and David Sobral

The little or no evolution of structure in Milky-Way-like galaxies up to z=2.23

Abstract: To map the evolution of Hα star-forming galaxies (SFGs) across cosmic time (i.e. approximately in the last 11 Gyrs) in an unbiased way, we have conducted multiple panoramic Hα narrow-band surveys (HiZELS and CF-HIZELS) over ~10deg2 using various narrow-band filters in the z, J, H and K bands (see Sobral et al. 2013, 2015) resulting in the largest single selection samples obtained thus far. These samples have allowed us to measure the Hα luminosity function evolution with unprecedented statistical significance (e.g. Sobral e al. 2013), but also to conduct evolutionary studies of a self-consistent sample between redshifts of 0.4 and 2.23 (e.g. Stott et al. 2013a; Swinbank et al. 2012a,b). Until now our results are consistent with a mild evolution scenario from SDSS (Stott et al. 2013b), which clearly shows the importance of having a clean, well-understood and self-consistent selection to prove evolution of various physical quantities. By exploiting our unique surveys and keeping in mind that one of the principal goals of extragalactic astrophysics studies has been to understand what drives the structure of galaxies, we have conducted a detailed structural analysis of our galaxies and of a local sample observed with CALIFA by running GALFIT (Peng et al. 2002, 2010), for a local Universe comparison. Comparing their morphological information (such as effective radius, Sérsic index, and ellipticity) with the available Hα maps, we were able to explore correlations with related quantities such as star-formation rate (SFR), stelar mass and rest-frame colors. Apart from those that directly depend on SFR, we find little to no evolution in most of the correlations. We will discuss the implications of a no-structural evolution scenario.

Ana Afonso and David Sobral

The perks of being a local galaxy

Abstract: While understanding how galaxies form and evolve requires to look at high look-back times (high redshift), there are important clues to be found in the local Universe. This is particularly important because nearby galaxies allow us to probe actual physical processes in a detail that not even 30-40m class telescopes will allow, for the most distant galaxies. In the advent of Integral Field Unit (IFU) instrumentation one is at the right time to start exploring all the perspectives of local galaxies using large surveys such as CALIFA (Sánchez et al. 2012), MaNGA (Law et al. 2014) and SAMI (Croom et al. 2012). The 3D spectroscopy technique combines spatial and spectral information that allows one to map the properties of different regions in galaxies and from that assemble the pieces that will help to build a much more complete understanding of galaxy formation and evolution. Here we present our efforts in not only trying to understand the physics of local galaxies, but also to obtain direct links to the most distant galaxies. We show how important it is to obtain measurements in the same way as at high redshift, but also evaluate biases that are inevitable at high redshift. Only by obtaining measurements in a self-consistent way can we actually make significant progress in understanding how galaxies like our own formed and evolved.

Ana Afonso, João Calhau, Sérgio Santos and David Sobral

Standing on the shoulders of giants

Abstract: The Isaac Newton Telescope (INT) is a 2.54 m optical telescope operating at the Observatorio del Roque de los Muchachos on the island of La Palma (Canary Islands, Spain) by the Isaac Newton Group of Telescopes (ING). Originally situated on the site of the Royal Greenwich Observatory at Herstmonceux Castle (where it saw its first light in 1967), it was moved away to La Palma due to the poor weather and light pollution. In 1984 the second first light was obtained and since then, INT is used for astrophysical research by a large community of astronomers worldwide having become one of the world's most productive 2-meter-class telescope. Modern astronomy relies less and less on the endless nights spent controlling a telescope to gather the data that we use for our day-to-day science. However practical it might be to have the dta you want being taken at some far away Observatory and then downloaded to your office one loses touch to what actually takes to observe a given target. Being immersed in the environment of active observations used for cutting-edge science is still possible at small scale telescopes such as the 2.5-meter INT. It is in such environments that students can concretize the processes that we learn about on astronomical courses. By having to take care of preparing an observation plan, acquire the necessary reduction files an the science data which will then be used to make new discoveries in astronomy (such as CR7-likes), students only gain from having access to observing time and actual interaction with the baseline instrument that we all use in optical/near-infrared astronomy. In addition to getting in touch with the basic notions of practical observational astronomy the students also gain in terms of responsibility and reaction skills as one must be in control of the telescope, the weather and the observing conditions to carry out a successful observing run without wasting precious time and by taking care of the precautions needed to prevent damage in the equipment. Here we present how participation in research programs can be used to train students in practical observation astronomy based on our own experiences while observing under the guidance of Doctor David Sobral at INT.

Hugo Messias, José M. Afonso, Mara Salvato, Bahram Mobasher and Andrew M. Hopkins

Identifying and characterizing the dusty AGN population with JWST

Abstract: When actively accreting, a super-massive black-hole will show a characteristic spectrum which may greatly dominate over that of its host. In this active galactic nucleus (AGN) phase, however, in the presence of large contents of gas and dust, the AGN-induced high-energy radiation may become elusive. The near-to-mid-infrared (nmIR) spectral range offers a means to trace this absorbed energy, since it will be "reprocessed" and emitted at these wavelengths by dust heated to high temperatures (~100—1500K). AIMS: By operating in this spectral range, the James Webb Space Telescope (JWST) will thus be a key facility to identify and characterize such obscured AGN population. METHODS: For this purpose, we have proposed and demographically characterized broad-band photometric AGN-selection nmIR-criteria especially suited for the JWST filter-set (Messias et al. 2012, 2014). They are built to be reliable against a ~10-20% error in flux. Specifically the JWST-tuned criterion aims to blindly identify AGN up to the re-ionization epoch (050—90% selected-candidates being confirmed AGN via X-ray and optical-spectroscopy analysis. AGN-selection in the nmIR is mostly dependent on AGN intrinsic luminosity, with some evidence for obscuration dependency at intermediate X-ray luminosities (43.3 < log(Lx[erg/s] ) < 44). We show that unobscured AGNe are intrinsically more luminous than obscured AGNe only at z<~1.6, thus resulting in more unobscured AGNe being selected when the IR survey is shallower. CONCLUSIONS: The JWST's broad-band filters 2.0um, 4.4um, 7.7um, and 18um will be essential for disentangling AGN from non-AGN dominated SEDs at depths where spectroscopy becomes impractical. The JWST high-resolution imaging and detection capabilities will be key to recover the lower luminosity obscured AGN population, especially when teamed up with deep hard-X-ray or radio surveys. Wide IR surveys are still needed to recover the rare powerful, obscured AGN population which JWST will then thoroughly characterize.

Masato Minamitsuji

Cosmological dynamics in the theory with field derivative coupling to the double-dual Riemann tensor

Abstract: The Horndeski theory is known as the most general scalar-tensor theory with the second order equations of motion and involve most of the known dark energy models. On the other hand, there should be new type of dark energy models in the Horndeski which have been less explored. Among the derivative interactions in the Horndeski theory, it has been argued that the particular class of couplings could realize the self-tuning of cosmological constant, namely the cosmological dynamics is not affected by a large cosmological constant /vacuum energy present in the theory. The most representative and well-studied case is the quadratic field derivative coupling to the Einstein tensor. The next and less studied case is the cubic field derivative coupling to the double-dual Riemann tensor which is the curvature tensor sharing the same symmetry with the Riemann tensor and being divergence free. We investigate cosmological dynamics in the presence of the field derivative coupling to the double-dual Riemann tensor. We show that the interplay with the galileon kinetic coupling can realize a self-accelerating solution and find the condition that this self-accelerating solution can be the late-time cosmological attractor.

David Sobral

What happens to galaxies when galaxy clusters merge? The Role of Cosmic Tsunamis

Abstract: Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Recently, unexpected overdensities of candidate Hα emitters near the ~1-Mpc-wide shock fronts of the massive (~2 x 10^15 Msun) `Sausage' merging cluster, CIZA J2242.8+5301. We used the Keck/Deep Imaging Multi-Object Spectrograph and the William Herschel Telescope/AutoFib2+WYFFOS to confirm 83 Hα emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster subcores (away from the shock fronts) show high [S II]6716/[S II]6761 and high [S II] 6716/H-alpha, implying very low electron densities (<30 × lower than all other star-forming galaxies outside the cluster) and/or significant contribution from supernovae, respectively. All cluster star-forming galaxies near the cluster centre show evidence of significant outflows (blueshifted Na D ~200-300 km s-1), likely driven by supernovae. Strong outflows are also found for the cluster Hα active galactic nucleus (AGN). Hα star-forming galaxies in the merging cluster follow the z ~ 0 mass-metallicity relation, showing systematically higher metallicity (~0.15-0.2 dex) than Hα emitters outside the cluster (projected R > 2.5 Mpc). This suggests that the shock front may have triggered remaining metal-rich gas which galaxies were able to retain into forming stars. Our observations show that the merger of impressively massive (~10^15 Msun) clusters can provide the conditions for significant star formation and AGN activity, but, as we witness strong feedback by star-forming galaxies and AGN (and given how massive the merging cluster is), such sources will likely quench in a few 100 Myr.