Astrophysics

Astrophysics Seminar History
Date	Room	Speaker	Title
Jun 20 2013 10:00	Room 135	Gianluca Castignani (SISSA)
ABSTRACT:
Jun 20 2013 11:00	Room 135	Jing Tang (SISSA)
ABSTRACT:
Jun 05 2013 14:00	Room 135	Yang Chen (SISSA)
ABSTRACT:
May 30 2013 14:00	Room 135	Rossella Aversa (SISSA)	The cosmological evolution of the Black Hole mass function
ABSTRACT:
Jan 17 2013 14:00	Room 135	Veronica Biffi (SISSA)	A novel virtual X-ray telescope for hydrodynamical simulations of galaxy clusters
ABSTRACT: X-ray observations continue to provide us with an increasingly detailed picture of galaxy clusters, for which a clear interpretation of the underlying physical processes is very challenging. While hydrodynamical simulations can currently address many of the questions about the cluster dynamics and physics, it is vital to find a faithful way to directly compare the output data from such simulations to real X-ray observations. For this purpose, I will present a novel virtual X-ray photon simulator devoted to obtain synthetic X-ray observations from hydrodynamical simulations, with special concern for, but not restricted to, galaxy clusters. This tool implements an original approach able to significantly gain\r\nin spectral resolution and computational cost with respect to similar codes.
Dec 13 2012 14:00	Room 135	Pawel Bielewicz ()	Studies of the cosmic microwave background at large angular scales
ABSTRACT: Studies of the cosmic microwave background (CMB) are today one of the most important pillars of observational cosmology. They provide information not only on the initial conditions of the Universe but also on scales comparable to the horizon of the observable Universe. This gives a unique opportunity to pose important questions about very fundamental assumptions made in the standard cosmological model such as statistical isotropy and Gaussianity of the initial fluctuations. Since the COBE and WMAP data releases, considerable effort has been spent on analyzing the statistical properties of the CMB maps at the large angular scales. Remarkably, this effort has resulted in several reports of a breaking of statistical isotropy, as established by many qualitatively different methods. I will review these studies and few hypotheses concerning the observed anomalies paying special attention to prospects of testing these hypotheses with future cosmological observations.
Nov 29 2012 14:00	Room 135	Alessandra Silvestri (SISSA)	Testing GR on cosmological scales and through screening mechanisms
ABSTRACT:
Nov 22 2012 14:00	Room 135	Arif Mohd ()	Holography and Hydrodynamics: Higher Curvature Gravity
ABSTRACT:
Nov 08 2012 14:00	Room 135	Francesco Paci ()	Exploring the CMB sky at large angular scales
ABSTRACT:
Oct 25 2012 14:00	Room 135	Ian Vega ()	Self-force for All
ABSTRACT: Motivated primarily by the prospect of detecting low-frequency\r\ngravitational waves with space-based observatories, over the past decade a lot of activity within gravitational physics\r\nhas centered on topics of self-force or radiation reaction in curved spacetime. The subject itself however is one of fundamental interest with applications that go beyond gravitational wave astronomy. In this talk, I shall go over the basics: what the self-force is, why it is challenging, and why it is important in a number of applications. I will end with a personal take on future prospects and a list of interesting open problems.
Apr 04 2012 15:00	Room 005	Andrea Lapi (Roma "Tor Vergata")	The Interplay between Dark Matter and Baryons in Cosmic Structures
ABSTRACT:
Mar 29 2012 14:00	Room 135	Jun-Qing Xia (SISSA)	Cross-correlation between CMB and LSS
ABSTRACT: Anisotropies in cosmic microwave background (CMB) data contain precious information on the large scale structure that formed at much lower redshift, which can be studied and detected by cross-correlating CMB data with tracers of the large scale structure (LSS) such as galaxies or quasars. In this talk, I will present the analyses of auto-/cross- correlations of SDSS QSO/NVSS radio samples with the WMAP7 temperature map in detail and use these data as a cosmological tool to study dark energy and non-gaussianity.
Mar 22 2012 14:00	135	Ranieri Baldi (SISSA)	Birth, life and death of Radio-loud Active Galactic Nuclei
ABSTRACT: A fundamental problem in studying the physics of Active Galactic Nuclei (AGN) is the identification of the mechanism that controls the level of activity. AGN activity is related to the growth, via cold and/or hot gas accretion, of supermassive black holes (SMBH). The clear evidence for a co-evolution of SMBH and host galaxies, represented by the connections between galaxy physical properties and SMBH mass, implies that the accretion process in AGN has a powerful influence on galaxy evolution and vice versa. More generally, in this scenario we investigate why nuclear activity occurs in some galaxies and not in others, what sets the level of activity along its "life" and which condition establishes its "death".
Mar 08 2012 14:00	SISSA, room 135	Ilias Cholis (SISSA)	Searching for dark matter annihilation signals in dwarf spheroidal galaxies
ABSTRACT: Dwarf spheroidal galaxies compose one of the most dark matter dominated classes of objects, making them a set of targets to search for signals of dark matter annihilation. The recent developments in gamma-ray astronomy, most importantly the launch of the Fermi-LAT instrument, have brought those targets into attention. Yet, no clear excess of gamma-rays has been confirmed from these targets, resulting in some of the tightest limits on dark matter annihilation from indirect searches. In extracting limits from dwarf spheroidal galaxies, it is of great importance, to properly take into account all relevant uncertainties, which include the dark matter distribution properties of the dwarf spheroidals, and uncertainties on the underlying background. I will revisit the limits on dark matter annihilation, from gamma-rays studying a set of close-by dwarf spheroidals, for which, there is good understanding of the uncertainties in the dark matter distribution. For those targets, I will show results from alternative methods in extracting the background gamma-ray flux,providing a method to discriminate among the dark matter annihilation targets, those that can give robust constraints. Finally I will present the tightest (conservative) limits on dark matter annihilation,coming only from the targets that ensure accurate understanding of both the gamma-ray background and the dark matter distribution uncertainties.
Feb 23 2012 14:00	Room 135	Antonella Garzilli (SISSA)	New perspectives in primordial black holes
ABSTRACT:
Feb 09 2012 14:00	Room 135	Claudio Cremaschini (SISSA)	Absolute stability of axisymmetric perturbations in strongly-magnetized collisionless axisymmetric accretion disk plasmas
ABSTRACT: The physical mechanism responsible for driving accretion flows in astrophysical accretion disks is commonly thought to be due to plasma instabilities (eg, axisymmetric magneto-rotational or thermal instabilities). In this talk the linear stability of axisymmetric electromagnetic perturbations occurring in magnetized collisionless accretion-disk plasmas is discussed. The kinetic equilibria which arise in these systems (Cremaschini et al. 2010-2012) are proved to be stable with respect to perturbations of this type. The analysis is carried out in the framework of the Vlasov-Maxwell kinetic description for accretion-disk plasmas. Basic aspect of the theory and the underlying physical mechanisms will be addressed.
Feb 02 2012 14:00	Room 135	Rudy Gilmore (SISSA)	Discussion of "Concordance models of reionization: implications for faint galaxies and escape fraction evolution" by Kuhlen and Faucher-Giguere (arXiv:1201.0757)
ABSTRACT: For this week's AP Journal Club, I will discuss the paper "Concordance models of reionization: implications for faint galaxies and escape fraction evolution" by Michael Kuhlen and Claude-Andr e Faucher-Giguere, preprint available at http://arxiv.org/abs/1201.0757. The goal of this paper is to outline the range of reionization scenarios that are consistent with present-day data. Following the paper, I will begin with an overview of the observational constraints that are currently available. The paper then describes a set of models which can simultaneously match these constraints, varying the escape fraction of ionizing photons from early galaxies and the minimum mass of star-forming halos. Each of these model variants implies a different possible scenario for the history of ionizing emissivity and for the duration of the reionization epoch.
Jan 26 2012 14:00	Room 135	Heng Hao (SISSA)	Spectral Energy Distributions of Type 1 AGNs in COSMOS
ABSTRACT: In this talk, I will present a detailed study of AGN SED shapes in the optical-near infrared for 413 X-ray selected Type 1 AGNs from the XMM-COSMOS Survey. I defined a near-IR/optical index-index ('color-color') diagram to investigate the mixture of AGN continuum, reddening and host galaxy contribution. We found that ~90% of the AGNs lie on mixing curves between the Elvis et al. (1994) mean AGN SED (E94) and a host galaxy, with only the modest reddening. However, ~10% of the AGNs have weak or non-existent near-IR bumps, suggesting a lack of the hot dust characteristic of AGNs (Hao et al., 2010). The mixing diagram is not only useful in identify outliers but can also show the proposed 'cosmic cycle' of SMBH and galaxy co-evolution (e.g. Hopkins et al., 2006) as evolutionary tracks, showing great potential of revealing how the SMBH and galaxy evolve during cosmic time.
Dec 15 2011 16:00	Room 135	Sandra Raimundo (SISSA)	Active Galactic Nuclei and the growth of supermassive black holes
ABSTRACT: Active Galactic Nuclei (AGN) are observed at various redshifts and environments, spreading over orders of magnitude in power, obscuration and mass. The energetic output observed from these sources is generated by accretion onto a supermassive black hole, a process which, although not resolved by our current instruments, can be inferred by multi-wavelength observations of the emitted radiation. In this talk, I will firstly introduce the main properties of AGN and then discuss several open questions such as: how does the material in our line of sight affect the observations of AGN? Can we model the evolution of AGN and the growth of black holes? And finally, is it possible to explore the accretion physics based on the observed AGN properties?
Dec 12 2011 16:00	Room 135	Ilia Musco (University of Oslo)	Causal horizons and black hole formation in the early universe
ABSTRACT: We present first a discussion of causal horizons, both for black holes and for the universe, emphasizing the similarities between the two situations. The discussion uses spherical symmetry but does not assume that the black holes are stationary or surrounded by vacuum, or that the universe is homogeneous. We then discuss issues concerned with cosmological structure formation in the early universe, showing results from recent simulations of primordial black hole formation. In this context a key feature is the phenomenon of critical collapse: before the black hole is actually formed, there is a close balance between gravity and pressure which gives rise to an intermediate state well-approximated by a self-similar solution realized only within the past light cone of the forming black hole. The masses of the black holes finally formed follow a scaling law with respect to the amount by which the amplitude of the initial perturbation exceeds a critical threshold.
Nov 29 2011 16:30	room 135	Isaac Vidana Haro (Universidade de Coimbra)	Symmetry energy, neutron star crust and neutron skin thickness
ABSTRACT: We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach using the realistic Argonne V18 nucleon-nucleon potential plus a phenomenological three-body force of Urbana type. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter L=66.5 MeV, compatible with recent experimental constraints from isospin diffusion, L=88�25 MeV. The correlation between the neutron skin thickness of neutron-rich isotopes and the slope L and curvature Ksym parameters of the symmetry energy is studied. Our BHF results are in very good agreement with the correlations already predicted by other authors using nonrelativistic and relativistic effective models. The correlations of these two parameters and the neutron skin thickness with the transition density from nonuniform to ?-stable matter in neutron stars are also analyzed. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.
Aug 02 2011 16:00	SISSA, room 005	Chris Matzner (Astronomy Department, McLennan Laboratories, Toronto, Canada)	Feedback processes in turbulent star formation
ABSTRACT: Star formation is the notoriously slow and inefficient process by which part of a cold, turbulent gas reservoir collapses while the remainder is dispersed. A theory for this process is necessary for any true understanding of the star formation rate within galaxies, the mass and multiplicity distributions of stars, the properties of stellar associations and clusters, and the initial conditions for planet formation — and, to underpin computer modeling. Although gravity is the dominant force, thermal and dynamical `feedback' is critical to the outcome of star formation. I shall focus on the importance and mechanisms of feedback, including magnetized outflows from young stars and the radiation pressure, ionization heating, winds and supernovae from massive stars, and the modulation of gravitational collapse. I'll discuss the implications for individual star formation, star cluster formation, and the evolution of giant molecular clouds.
Apr 13 2011 16:00	SISSA, room 135	Eugene Lim (DAMTP, University of Cambridge)	Modified Gravity makes Galaxies Brighter
ABSTRACT:
Nov 11 2010 16:00	SISSA, room 005	Jason Penner (University of Southampton)	General Relativistic Magnetohydrodynamic Bondi-Hoyle Accretion
ABSTRACT:
Oct 21 2010 16:00	SISSA, room 005	Ray Rivers (Imperial College, London, UK)	Condensates meet Cosmology
ABSTRACT: There are several ways in which our knowledge of condensates informs our understanding of cosmology. Most simply, cold dark matter has been represented by Bose-Einstein condensates whereas, at the other extreme, AdS/CFT duality enables us to use black hole physics to describe a condensate in its conformal regime. In this talk I shall concentrate on the roles that causal horizons and event horizons play in tunable condensates. Concentrating on experimentally accessible tunable cold fermi gases I shall propose experiments for observing causal horizons but argue that that such systems are problematic for providing analogue gravity metrics.
Jun 24 2010 16:00	SISSA, Room 135	Cosimo Bambi ( Institute for the Physics and Mathematics of the Universe, University of Tokyo, Japan)	Testing strong gravity with future VLBI observations
ABSTRACT:
Mar 04 2010 12:00	Villa Bazzoni	Silvio Bonometto (Univ. Milano-Bicocca, Italy)	Neutrino mass and dark cosmic components
ABSTRACT: Cosmological models with a linear coupling between CDM and DE, and with a sum of neutrino masses ~1eV, fit observational data better than LCDM (at ~2 sigma). Within 2 years, Tritium decay experiments will test this mass range, possibly making LCDM cosmologies obsolete.
Jul 07 2009 16:00	SISSA, Room D	Lara Nava (INAF - Brera Astronomical Observatory)	Gamma-Ray Bursts: theory and observations
ABSTRACT:
Jun 25 2009 16:00	SISSA, Room E	Valerio Faraoni ( Bishop University, Canada)	Cosmological expansion and local dynamics
ABSTRACT: Assuming that the Friedmann metric is valid down to small scales, do local objects expand with the universe or resist the expansion? This long-standing issue will be revisited with the help of new exact solutions describing black holes embedded in cosmological backgrounds. Apart from the (static) de Sitter background, even the most strongly bound object, the black hole, participates in the expansion of the cosmic substratum. Issues of interpretation and genericity of the new exact solutions will be discussed.
Mar 04 2009 16:00	SISSA, Room E	Mariangela Bernardi (University of Pennsylvania, Philadelphia, USA)	Massive galaxies in massive datasets
ABSTRACT: Understanding why massive early-type galaxies are red and dead has proved to be difficult. This has been the source of tension with hierarchical formation models, such as the Cold Dark Matter model, in which massive objects are formed from mergers of smaller ones which existed at early times. The problem is to arrange for star formation to occur at higher redshift than the actual assembly of the stars into a single massive galaxy. The most recent galaxy formation models arrange for this to happen by a combination of two processes: dry mergers and AGN feedback. I will discuss a number of results on massive galaxy formation that are based on analyses of Brightest Cluster Galaxies and other extreme objects in the SDSS and other recent astrophysical datasets.