Astrophysics Seminar History
| Date |
Room |
Speaker |
Title |
Nov 15 2023
16:00 |
Room 135
|
Ugo Niccolò Di Carlo
(SISSA - APC)
|
Black Holes in Young Star Clusters |
ABSTRACT: Young Star Clusters (YSC) are unique and densely populated environments which can host 10^3-10^6 stars. The vast majority of massive stars, i.e. the progenitors of black holes (BHs), are known to form in YSCs. In this talk, I will discuss some key findings regarding BHs in YSCs.rnSpecifically, I will present the results of an extensive series of direct N-body simulations of YSCs with large primordial binary fraction, novel population-synthesis prescriptions and fractal initial conditions to mimic the clumpiness of star forming regions. rnThese simulations shed light on the formation of merging binary black holes (BBHs), and their distinctive signatures which characterize different formation pathways and environments. These insights offer valuable clues for disentangling the formation history of systems detected by the LVK collaboration. rnI will show how in my simulations, thanks to multiple stellar collisions and dynamical exchanges, we form peculiar objects and binary systems, such as merging BBHs with members in the pair instability mass gap, and intermediate mass black holes with masses up to ~500 Msun. rnAdditionally, I will discuss the possibility that the two BH-Star systems detected by the Gaia mission, namely Gaia BH1 and Gaia BH2, might have formed within YSCs rather than in isolation.rnLastly, I will address the forthcoming challenges and the next steps in both the numerical simulations and the scientific investigations of BHs in YSCs. |
Oct 30 2023
14:00 |
Room 135
|
Ivan De Mitri (tbc)
(GSSI)
|
Recent observations on high energy cosmic rays |
ABSTRACT: TBD |
Sep 26 2023
11:00 |
room 128-129
|
Alex Sicilia (Ph.D. defence)
(SISSA)
|
The Black Hole Mass Function: From Stellar to Supermassive |
ABSTRACT: |
Jun 27 2023
14:00 |
Room 135
|
Facundo Rodriguez
(National University of Cordoba)
|
Analysis of central galaxy alignments through the anisotropic correlation function |
ABSTRACT: In this seminar, we present the study of the alignment of central galaxies with the surrounding structures and satellite galaxies in their group/halo. To perform this analysis, we use a modified version of the two-point cross-correlation function. We use both observational data from the Sloan survey (SDSS DR16) and simulations (Illustris TNG300-1) and the results obtained allow us to relate the alignment to the halo assembly process as it can be explained by a combination of physical processes on different scales: the central galaxy aligns with the dark matter halo it inhabits, and this, in turn, aligns with the surrounding structures on large scales. |
Jun 06 2023
14:00 |
room 135
|
Laia Barrufet
(Univ. Geneve)
|
Unveiling the Nature of Infrared Bright, Optically Dark Galaxies with Early JWST Data |
ABSTRACT: Over the last few years, low-resolution infrared observations have revealed a population of optically-dark galaxies undetected with HST, the so-called HST-dark galaxies. We know that these galaxies are likely to be massive and at z>3. However, due to the limited photometry in infrared wavelengths, the true nature of these galaxies has remained elusive. For the first time, the JWST is providing data that allows us to characterise these galaxies.In this talk, I will present the results of 30 HST-dark sources selected based on their red colours across 1.6 to 4.4 microns with NIRCam imaging from the Early Release Science Program CEERS. These galaxies are generally heavily dust-obscured, massive, star-forming sources at z~2-8. Our analysis shows the unique power of JWST to reveal this previously missing galaxy population and to provide a more complete census of galaxies at z>3 based on rest-frame optical imaging. Interestingly, HST-dark galaxies present a considerable contribution to the obscured star formation red density at z~7, already in the Epoch of Reionization.I will also present the first spectra of HST-dark galaxies with NIRSpec observations to show for the first time their spectroscopic redshifts from my program 'Quiescent or dusty? Unveiling the nature of extremely red galaxies at z>3' |
May 30 2023
14:00 |
room 135
|
Hao Fu
(Southampton university)
|
The impact of the stellar mass-halo mass relation and scatter in galaxy merger and star formation histories |
ABSTRACT: The role of mergers and star formation in regulating galaxy growth is still a matter of hot debate in astronomy. We use our Discrete statistical sEmi-empiriCal mODEl (DECODE) to predict, in a full cosmological context, the merger and star formation rates, and their respective contribution in the total mass assembly of galaxies. DECODE uses statistical realizations of dark matter haloes along with their subhalo merger trees, which are subsequently populated with galaxies via input stellar mass-halo mass (SMHM) relations. We compute the SMHM relations via abundance matching between the halo and galaxy mass functions. Then, galaxy merger histories are computed from halo merger trees via the SMHM relation and an assumed dynamical friction timescales. Star formation histories are retrieved simply via the difference between the total mass assembly and the merger history. With this methodology we get rid of any analytical parametrization of galaxy observables, making the model extremely transparent with very few parameters and inputs, being the SMHM relation and the dynamical friction. We find that only SMHM relations, implied by stellar mass functions with significant time evolution above 10^11 solar masses and poor evolution below that mass, can simultaneously reproduce the local satellite abundances, major merger rates, elliptical fractions and star formation histories from SEDs. |
Mar 14 2023
14:00 |
room 135
|
Matus Ribak
(Delft Univ., Netherlands)
|
Full of Orions? Dissecting dusty galaxies in the early Universe |
ABSTRACT: The first few Gyr after the Big Bang are the most dramatic chapters of the cosmic history. Half of all stars formed in this epoch, mainly in dust-enshrouded, sub-mm bright galaxies. However, these dusty giants are often invisible to optical telescopes and have to be studied at far-IR/mm-wavelengths, with limited spatial resolution, sensitivity, and bandwidth. Thus, despite two decades of effort, key characteristics of high-redshift dusty galaxies - how is their star formation distributed? how does it relate to their diffuse and dense gas content? - remain uncertain.rnrn rnrnThankfully, rapid advances in mm-wave technology are helping dissect galaxies in the early Universe in unprecedented detail and complexity. I will showcase recent results from high-resolution, high-sensitivity studies of the obscured star formation and gas content of dusty galaxies, achieved using ALMA, NOEMA, and VLA. These provide first views of the complex morphologies and extreme conditions in these distant galaxies, from their star-forming centers to the circumgalactic medium. Finally, I will outline the challenge for the 2030's: scaling these studies up to hundreds of galaxies via a massive, SDSS-like surveys at sub-mm wavelengths using ultra-wideband spectroscopy. |
Mar 07 2023
14:00 |
Room 135
|
Brivael Laloux (tbc)
(Athens Observatory)
|
Demographics of obscured AGN: a multiwavelength analysis |
ABSTRACT: Active Galactic Nuclei (AGN) are supermassive black holes (SMBH) growing during an intense accretion phase. The space density and the specific accretion rate distribution are two key parameters to quantify the growth of SMBHs. The first corresponds to the number of AGN as a function of the redshift and luminosity. The second one represents the probability of hosting an AGN with a specific accretion rate (sBHAR) as a function of the redshift and luminosity.
However, the presence of dust and gas on the line of sight obscuring the central source makes the identification and characterisation of AGN more challenging.
We propose a new Bayesian approach to measure the level of obscuration in deep extragalactic surveys. This methodology uses multiwavelength priors on the bolometric AGN luminosity to guide the X-ray spectral analysis and yield improved constraints on the physical properties of the AGN.
We apply this method to the deep multiwavelength observations in the Chandra COSMOS-Legacy field to provide a new sample of heavily obscured and Compton-thick AGNs. By combining it with an accurate characterisation of the X-ray selection function of the Chandra COSMOS-Legacy survey, we estimate in a non-parametric manner the X-ray AGN space density as a function of the line-of-sight obscuration. Our analysis also provides new constraints on the Compton thick AGN fraction out to $z sim2$, and our results deviate from popular X-ray luminosity functions in the literature.
We then extend our original sample to other X-ray surveys to increase the statistics of our analysis. By testing different SED fitting algorithms, we obtain the stellar masses of the AGN host galaxies needed to compute their accretion rate and, finally, constrain the sBHAR distribution as a function of the obscuration. We find accretion rate differences between obscured and unobscured sources.
I will discuss the importance of using multiwavelength information to guide X-ray spectroscopy, especially to study the faintest and most obscured sources. |
Feb 07 2023
14:00 |
room 135
|
Luca Sala
(Universitäts-Sternwarte München)
|
Black hole spin evolution in hydrodynamical simulations: a step towards AGN jet feedback modelling. |
ABSTRACT: Central massive black holes (BHs) and their host galaxies are thought to co-evolve due to the interaction that arise when the BHs accrete gas and release a large amount of energy back into the surrounding environment, which in turn affect the BH fuel reservoir. Numerical simulations are a powerful tool to study such a complex, non-linear interaction, but usually we are not able to resolve all the relevant scales involved, due to limited computational resources, therefore we have to rely upon sub-grid, effective models. I will present my work, which focuses on the design and implementation of such models for accretion and feedback, to be applied in cosmological hydrodynamical simulations. Regarding the treatment of accretion, I added an intermediate step in the mass transfer from the resolved scales of a simulation onto the BH, through the inclusion of a sub-grid accretion disk. The model self-consistently evolves the disc properties as well as the BH spin due to gas accretion and I will present results of simulations that test such a model in idealised setups as well as in a fully cosmological context, that allows to carry out statistical studies on the distribution of spins and radiative efficiencies. The direction and magnitude of the BH spin will eventually be used as input for a prescription of energy injection, that aims at reproducing the interaction of jets from AGNs with the surrounding medium, as we observe in features like radio lobes. |
Jan 24 2023
14:00 |
Room 135
|
Stefano Torniamenti
(University of Padova)
|
Formation channels of binary black holes in young star clusters |
ABSTRACT: A large fraction of massive stars forms in clusters, as member of binary and higher order systems. Thanks to the very high densities of the cluster cores, these systems can actively interact with the host environment from the very beginning of their life. This leaves a deep imprint on the binary properties and, eventually, results in binary black holes (BBHs) characterized by distinctive signatures with respect to the isolated ones. Understanding the peculiar imprint of this evolutionary scenario is of fundamental importance to disentangle the formation channels of the detected gravitational wave sources.
I will show the populations of BBHs that result from the evolution in star clusters of different masses, ranging from some hundreds solar masses, where the evolution is more similar to the isolated scenario, up to some thousands solar masses, in which the higher rates of exchanges and three-body interactions produce a large number of dynamical binaries.
I will show that different stellar environments result in extremely different BBH populations. Among the most distinctive features of the evolution in dynamically active clusters, there is the formation of black holes with primary mass in the pair-instability mass gap, via either stellar collisions (in which a main-sequence star merges with a more evolved star) or via BBH mergers. Finally, repeated mergers may even result in intermediate-mass black holes. |
Jan 17 2023
14:00 |
Remote only - https://sissa-it.zoom.us/j/83744446129?pwd=QTZDN1c5aXZjRGdVeXZwNkZIQlVrUT09
|
Giulia Cusin
(University of Geneva)
|
Astrophysical gravitational wave background: from theoretical modelling to detection prospects |
ABSTRACT: When looking at a population of astrophysical gravitational wave sources we can either decide to focus on those sources that are particularly bright, and build a catalogue, or characterise collectively the superposition of all signals from all sources from the onset of stellar activity until today. This stochastic background of gravitational radiation is an interesting observable as it can allow us to extract astrophysical information that cannot be extracted from the study of individual events. In this talk, I will give an overview of different astrophysical populations expected to generate a stochastic background in the frequency band of current and future gravitational wave detectors. I will then review the state of the art of background modeling and illustrate future detection prospects. |
Dec 06 2022
14:00 |
Room 135
|
Marcos Muniz Cueli
(SISSA)
|
The submillimeter galaxy magnification bias as a cosmological probe |
ABSTRACT: In recent years, the galaxy-mass cross-correlation has predominantly been probed within weak gravitational lensing via the correlation between foreground positions and background galaxy ellipticities. However, the cross-correlation between the positions of background and foreground galaxies is an alternative observable which, up to now, has been largely overlooked. The corresponding signal is a manifestation of the gravitational lensing effect of magnification bias and has been shown to become extremely significant when using a background sample of submillimeter galaxies. In this talk, I will discuss how this submillimeter galaxy magnification bias can be effectively exploited as a cosmological probe. |
Sep 29 2022
14:00 |
Room 135 and Zoom - https://sissa-it.zoom.us/j/89416894040?pwd=QU9NMkdkOG9IR2N3MXRlQjBEM21rQT09
|
Susanna Azzoni
(University of Oxford)
|
Detecting the CMB B-mode through foregrounds: a hybrid component separation approach |
ABSTRACT: Detecting the imprint of inflationary gravitational waves on the B-mode polarization of the Cosmic Microwave Background (CMB) is currently one of the most compelling fundamental science cases for cosmology. Arguably the largest source of systematic uncertainty for both space and ground experiments will be contamination by the astrophysical foreground signal from the Milky Way. The separation of CMB radiation and foregrounds can be performed either in real space or in Fourier space. Different CMB experiments have followed either approach, revealing their advantages and caveats. The effects of the different approaches will become crucial at the sensitivity of the forthcoming CMB experiments. In this talk I will present a two-step self-consistent hybrid method. This method combines the advantages of both approaches, by cleaning out the spatially-constant part of the foregrounds at the map level, assuming nothing about the scale dependence of foregrounds, and modelling the residual frequency maps at power-spectrum level. We validate the method using Simons-Observatory-like simulated observations, recovering an unbiased estimate of the tensor-to-scalar ratio r for a wide range of realistic foreground scenarios. |
Jul 01 2022
14:00 |
Hybrid: Room 135 and Zoom (https://sissa-it.zoom.us/j/88178687190?pwd=enhJZFZTN3JVMGRndVl5bDA3YzJZUT09)
|
Elias Kammoun
(IRAP - Observatoire Midi-Pyrénées)
|
Modelling thermal reverberation in active galactic nuclei |
ABSTRACT: Several active galactic nuclei (AGN) show UV/optical variability lagging behind the X-ray emission by a few days. The simplest and most straightforward interpretation is that the variable X-ray flux from the corona illuminates the accretion disc below where it is partially reflected and observed as fast X-ray reverberation signal, and partially absorbed and thermalised in the disc, which produces a slow UV and optical reverberation signal. Since the corona is thought to be centrally located and very small compared to the accretion disc, it first illuminates the hottest inner parts of the accretion disc and later on its colder further out areas. Thus one expects to see the original X-ray fluctuations to be firstly followed by variations in the UV and then in the optical wavebands.\r\nIn this talk, I will present our newly developed full GR-ray-tracing code, KYNxiltr, that computes the thermally reverberated UV/optical continuum responding to X-ray illumination by a compact corona. Our code considers the mutual interaction of the accretion disc and the X–ray corona. I will discuss how the properties of the system (e.g., black hole spin, accretion rate, corona height, etc.) affect the UV/optical time lags and present our results from modelling the observed lags obtained from long monitoring of bright local AGN. |
Jun 14 2022
14:00 |
https://sissa-it.zoom.us/j/87988506065?pwd=b25wTnNObDhzREQ2VXdyeUxLeEVRUT09
|
Alessandro Romeo
(Chalmers University of Technology)
|
Disc gravitational instability has a strong impact on galaxy scaling relations |
ABSTRACT: It is well known that gravitational instability is one of the engines behind the dynamics of disc galaxies, where it enters a variety of processes. Brand new work is demonstrating that disc gravitational instability has even a strong impact on galaxy scaling relations. In this talk, we will look at the atomic gas-to-stellar and stellar-to-halo mass relations from such a new perspective, we will show that such new diagnostics can be used as critical tests for simulations of galaxy formation and evolution, and we will finally discuss an intriguing astrophysical implication. |
Apr 05 2022
14:00 |
Hybrid: Room 128-129 and Zoom (https://sissa-it.zoom.us/j/83526291613?pwd=ZXRIcldFdmdhdVZXa3ZGa1BDNlp4Zz09)
|
Dr. Federico Levi
(Nature)
|
Inside Nature |
ABSTRACT: Since its launch in 1869, Nature has seen its mission as two-fold: facilitating the prompt communication of the most important scientific developments to the relevant research communities, while at the same time fostering a greater appreciation of these great works of science amongst the wider public. In this talk, I will endeavour to explain how Nature editors apply these principles in practice, in particular by determining which few of the many excellent research submissions that we receive make it through to publication. Questions and comments welcome. |
Feb 09 2022
14:00 |
Hybrid: Room 135 and Zoom (https://sissa-it.zoom.us/j/89305402146?pwd=RnJaS296cjVkUTZkb0VjZ3NZekh1Zz09)
|
Alessandro Trani
(University of Tokyo)
|
Three-body problems in astrophysics and beyond |
ABSTRACT: The gravitational few-body problem is one of the oldest conundrums in astronomy and classical mechanics. Yet, its simplest instance, the three-body problem, has no general analytical solution, and only a partial statistical solution has been achieved so far. With the birth of gravitational wave astronomy and the rise in exoplanet discoveries, the three-body problem is again becoming central to explaining astrophysical phenomena.rnI will describe our recent efforts in deriving a complete statistical solution to the non-hierarchical, chaotic three-body problem. I will then review the status of gravitational wave detections, and show how three-body interactions play a key role in several formation pathways of gravitational wave sources. |
Oct 26 2021
14:00 |
Hybrid: Room 005 and Zoom (https://sissa-it.zoom.us/j/82646728393?pwd=bk9qbDNEaWVJL29lRGF6VjJIVFFIQT09)
|
Prof. Andrew Jaffe
(Imperial College, London)
|
Bayesian Hierarchical Models in Cosmology |
ABSTRACT: |
Oct 25 2021
9:00 |
Hybrid: Room 128-129 + zoom
|
APC PH.D. DEFENCE: Hasti KHORAMINEZHAD
(SISSA, Trieste, Italy)
|
New avenues for investigating the Large-Scale Structure of our Universe |
ABSTRACT: |
Oct 18 2021
11:00 |
Hybrid: Big Meeting Room 7th floor + zoom
|
APC PH.D. DEFENCE:
Lumen BOCO
(SISSA, Trieste, Italy)
|
Gravitational waves throughout galaxy evolution: stellar black hole mergers and heavy supermassive black hole seeds |
ABSTRACT: |
Oct 11 2021
11:00 |
Hybrid: Big Meeting Room 7th floor + zoom
|
APC PH.D. DEFENCE:
Lara PANTONI
(SISSA, Trieste, Italy)
|
High-redshift Dusty Star Forming Galaxies: a panchromatic approach to constrain galaxy evolution |
ABSTRACT: |
Oct 06 2021
16:00 |
Hybrid: Room 005 and Zoom (https://sissa-it.zoom.us/j/85011931402?pwd=QWMzblZWRHA4RlRIQXpjMm95UDM2Zz09)
|
Louis Legrand
(University of Geneva)
|
CMB lensing power spectrum with deep polarisation experiments |
ABSTRACT: Gravitational lensing of the CMB is a powerful probe of the growth of structures. As such it will allow upcoming experiments to give, among other things, strong constraints on the sum of the neutrino mass. \r\nThe current estimation technique of the CMB lensing power spectrum, based on a quadratic estimator (QE), is mature and straightforward. However, for future deep polarisation CMB experiments, lensing potential maps reconstructed by iteratively removing the lensing-induced B mode signal will greatly improve over the standard approach.\r\n\r\nIn this talk I will introduce a new CMB lensing power spectrum estimator and its likelihood, based on iterative mass map reconstruction. I will show that despite the increased complexity of the maps, we can define an estimator very similar to the traditional QE based approach. I will show that for a CMB-S4 experiment, the iterative estimator greatly lowers the variance of the power spectrum on a wide range of scales, and increase the signal to noise ratio by a factor of two. \r\nMost interestingly, I will introduce a realisation dependant debiasing, similar to the QE, which allows our estimator to remain unbiased even under poor understanding of the noise properties.\r\nFinally I will demonstrate the power of our estimator to constrain the sum of neutrino mass with CMB-S4. |
Oct 05 2021
15:30 |
Hybrid: Room 128-129 and Zoom (https://sissa-it.zoom.us/j/85979590422?pwd=TVNFRXNrclZJZDBnQ2RSdW90N3lEUT09 )
|
Francesca Rizzo
(DAWN/Interactions Fellow - Cosmic Dawn Center, Niels Bohr Institute)
|
Strong lensing as a natural telescope: high resolution dynamical studies of z ~ 4.5 dusty star-forming galaxies |
ABSTRACT: The kinematics of high redshift galaxies reveals important clues on their formation and assembly, providing also strong constraints on galaxy formation models. Measurements of the gas rotation allow us to trace the distribution of the different matter components and study galaxy scaling relations. In contrast, measurements of the gas velocity dispersions give information about the turbulence within the interstellar medium, mainly driven by stellar feedback and gravitational instabilities. At the moment, studies of high-z galaxies are strongly affected by the limited angular resolution and sensitivity of the existing telescopes. Strong gravitational lensing provides a unique tool for overcoming these limitations, allowing to study the internal motions of high-z galaxies.\r\nIn this talk, I will present the dynamical properties of a sample of strongly gravitationally lensed dusty star-forming galaxies (DSFGs) at z ~ 4.5 on sub-kpc scales, obtained using ALMA observations of the [CII] emission line. This is the largest sample of 𝑧 ∼ 4.5 galaxies with high-quality data and sub-kpc spatial resolutions, so far. The kinematic properties of these galaxies demonstrate that at least some young galaxies are dynamically akin to those observed at low redshift, and only weakly affected by the extreme physical processes that characterize the early Universe. The relation between their velocity dispersions and their star-formation rates indicates that stellar feedback is sufficient to sustain the turbulence within these galaxies and no further mechanisms, such as gravitational instabilities, are needed. Finally, I will then show some results on the study of the evolutionary connection between the population of high-z DSFGs and the local early-type galaxies. |
Oct 04 2021
9:00 |
Hybrid: Room 128-129 + zoom
|
APC PH.D. DEFENCE:
Gauri SHARMA
(SISSA, Trieste, Italy)
|
The Nature of Dark Matter from the Astrophysics of High-z Star-forming Galaxies |
ABSTRACT: |
Sep 17 2021
14:00 |
Hybrid: Room 128-129 + zoom
|
APC PH.D. DEFENCE:
Samuele CAMPITIELLO
(SISSA, Trieste, Italy)
|
Relativistic accretion disk models for Active Galactic Nuclei: mass and spin of Supermassive black holes |
ABSTRACT: |
Oct 23 2020
14:00 |
Remotely
|
APC PH.D. DEFENCE: Paolo CAMPETI (SISSA)
(https://sissa-it.zoom.us/j/94576816760?pwd=ck9iZENvMjVzV0NQNklrU29JN1gyZz09)
|
Towards Precision Measurements of the Primordial Power Spectrum of Gravitational Waves: Combining B-mode Cosmic Microwave Background and Gravitational Waves Observations |
ABSTRACT: The common thread of my research as a PhD student in the Astrophysics & Cosmology Group at SISSA has been the primordial stochastic gravitational wave background (SGWB). In fact, the production of a primordial SGWB is predicted by the inflationary paradigm, one of the cornestones of the current Standard cosmological model: this scenario predicts indeed the generation of tensor perturbations by vacuum quantum fluctuations. As of today, these inflationary tensor perturbations still remain undetected. The importance of their detection cannot be overestimated, since this primordial SGWB contains an unparalleled amount of information on the very early Universe physics, and furthermore, if the standard single-field slow-roll inflationary scenario is confirmed, a detection of the primordial tensor modes would allow to directly infer the energy scale of inflation, allowing us to probe ultra-high energy scales, not accessible by terrestrial particle colliders. Given the importance of this discovery, several experiments are operating or are planned for the near future, both searching for the signature of the SGWB in the CMB polarization B-modes and looking for a direct detection using gravitational wave laser interferometers and Pulsar Timing Arrays. During my PhD, I explored both these observational paths, performing forecasts and quantifying the challenges for detection for both kind of experiments. |
Oct 06 2020
13:30 |
Remotely
|
APC PH.D. DEFENCE: Tommaso RONCONI (SISSA)
(https://sissa-it.zoom.us/j/99946538303?pwd=RHRCd2t6KzIyVzU4WmRWUnpBSE5DQT09)
|
From cosmic voids to collapsed structures: HPC methods for Astrophysics and Cosmology |
ABSTRACT: My work as a PhD student in the Astrophysics and Cosmology Group at SISSA was focused on the development and testing of original computational tools. I have completed a project on the exploitation of the size function of cosmic voids as a cosmological probe. Cosmic voids occupy most of the volume of the Universe, and their statistical properties can be exploited for constraining dark energy, as well as for testing theories of gravity. Nevertheless, in spite of their growing popularity as cosmological probes, a gap of knowledge between cosmic void observations and theory still persists. In our research we attempted in covering this gap, by developing a consistent theory for the size distribution of cosmic voids identified in biased tracers of the density field. Afterwards we focused on the development of a stand-alone software package for the analysis of observed clustering statistics of different order and the production of empirical models for galaxy mock catalogues. We have extensively tested our software both scientifically and in terms of performance and the application has been made publicly available. Empirical models are by design particularly suitable for addressing the modelling of the high redshift Universe, but they rely on the availability of high redshift observations of the population to be modelled. I have used our application to perform a preliminary study on the spatial distribution of ionized bubbles during Reionization, using observations of Lyman Break Galaxies in the redshift window 4 |
Sep 28 2020
11:00 |
Remotely
|
APC PH.D. DEFENCE: Gabriele PARIMBELLI (SISSA)
(https://sissa-it.zoom.us/j/97812716788?pwd=bDV3dGl5YWZtVGM2YXZmZzRadWJTZz09)
|
The impact of cosmological neutrinos on large-scale structure observables |
ABSTRACT: My research as a Ph.D student in the Astrophysics & Cosmology Group at SISSA was focused on the impact of neutrinos on the main cosmological observables of large-scale structure. In fact, while according to the Standard Model of particle physics neutrinos are massless, flavor oscillation experiments have highlighted how they do possess a mass, which however has not been measured yet. Cosmology has the power to do so, thanks to the slowdown that neutrinos cause to the growth of cosmic structures like galaxies and clusters of galaxies: indeed, upcoming surveys will likely be the first to measure neutrino mass using these probes. I carried out my research with the goal of assessing the effect of neutrino mass on the observables that will be employed in these future experiments. |
Nov 12 2019
16:30 |
room 135
|
Jochen Weller
()
|
Cosmology with Clusters of Galaxies |
ABSTRACT: |
Jun 18 2019
14:30 |
room 135
|
Eiichiro Komatsu
(MPA , Garching)
|
Finding Cosmic Inflation |
ABSTRACT: The cosmic microwave background (CMB) research told us a\r\nremarkable story: the structure we see in our Universe such as galaxies,\r\nstars, planets, and eventually ourselves originated from tiny quantum\r\nfluctuations generated in the early Universe. With the WMAP we have\r\nconfirmed many of the key predictions of inflation including flatness and\r\nstatistical homogeneity of our Universe, Gaussianity and adiabaticity of\r\nprimordial density fluctuations, and a small but non-zero deviation from the\r\nscale-invariant spectrum of density fluctuations. Yet, the extraordinary\r\nclaim requires extraordinary evidence. The last prediction of inflation that\r\nis yet to be confirmed is the existence of primordial gravitational waves\r\nwhose wavelength can be as big as billions of light years. To this end we\r\nhave proposed to JAXA a new satellite mission called LiteBIRD, whose primary\r\nscientific goal is to find signatures of gravitational waves in the\r\npolarisation of the CMB. In this presentation we describe the current state\r\nof affairs regarding our understanding of the early Universe, physics of\r\npolarisation of CMB, the LiteBIRD proposal, as well as a sub-mm telescope in\r\nChile called CCAT-p that we are currently building. |
Mar 19 2019
14:00 |
room 135
|
Francesco Shankar
()
|
|
ABSTRACT: |
Jan 29 2019
14:00 |
room 135
|
Nilay Bostan
()
|
|
ABSTRACT: |
Nov 20 2018
14:00 |
room 135
|
Vibor Jelić
(Ruđer Boković Institute, Zagreb, Croatia)
|
Mysterious structures in our Galaxy obscuring the view towards the first stars in the Universe |
ABSTRACT: Recent LOFAR (Low Frequency Array) observations revealed a bewildering variety of structures in polarisation in several fields at high Galactic latitudes. The structures are found at different Faraday depths, which measures the product between the electron density of the ionized gas and the line-of-sight magnetic field. One of the fields, 3C196 field, shows the most interesting features. Notably, a few degrees straight filament, which displaces in Faraday depth the background synchrotron emission. While its physical parameters are hard to pinpoint, this is likely a filament of ionized gas located somewhere within the local bubble. Together with another structure observed in the same field it correlates with observed HI filaments and the magnetic field orientation probed by the Planck observations of the dust emission in polarisation. This result is quite surprising as LOFAR, Planck and HI observations are sensitive to different ISM phases. In addition, there is a conspicuous system of long and straight depolarisation canals aligned with the magnetic field. During my talk I will present and discuss these intriguing results, as well as, how they might obscure the view towards the first stars in the Universe - the LOFAR-Epoch of Reionization key science project. |
Oct 09 2018
14:00 |
room 135
|
Lorenzo Posti
()
|
tba |
ABSTRACT: tba |
Sep 26 2018
14:00 |
room 128-129
|
Chiara Mingarelli
(Center for Computational Astrophysics, Flatiron Institute)
|
MULTIMESSENGER SEMINAR SERIES: Pulsar Timing Arrays - The Next Window to Open on the Gravitational-Wave |
ABSTRACT: Universe Galaxy mergers are a tandard aspect of galaxy formation and
evolution, and most (likely all) large galaxies contain supermassive
black holes. As part
of the merging process, the supermassive black holes should in-spiral
together and eventually merge, generating a background of gravitational
radiation in the nanohertz to microhertz regime. An array of precisely
timed pulsars spread across the sky can form a galactic-scale
gravitational wave detector in the nanohertz band. I describe the
current efforts to develop and extend the pulsar timing array concept,
together with recent limits which have emerged from international
efforts to constrainastrophysical phenomena at the heart of supermassive black
hole mergers. |
Sep 25 2018
14:00 |
room 128-129
|
Peter Veres
(University of Alabama in Huntsville)
|
MULTIMESSENGER SEMINAR SERIES: Gamma-ray burst science at the advent of multi-messenger astrophysics |
ABSTRACT: I will discuss topics related to gamma-ray burst (GRB) science including very high-energy emission, polarization modeling aspects and the discovery of the first electromagnetic counterpart of a gravitational wave event. GRBs are the most luminous explosions in the universe. Understanding the underlying physical processes is one of the most challenging questions in modern astrophysics. First I will discuss the detection prospects of GRBs at very high-energies, E>0.1 TeV which are important for the upcoming Cherenkov Telescope Array and will provide clues to the emission mechanism of GRBs. Next, I will talk about efforts to determine the composition of GRB jets: energy can either be carried by baryons or by magnetic fields. Upcoming polarization measurements can have an important role in deciding between these two possibilities. I will discuss how a joint effort between Fermi-GBM and AstroSAT brings us closer to answering these questions. Finally, I will talk about the first multi-messenger observation of a GRB related to the binary neutron star merger event, GW170817 observed through gravitational waves by LIGO and Virgo. I will describe my contribution and Fermi-GBM's role in deciphering one of the most widely followed astronomical event. |
Sep 25 2018
15:00 |
room 128-129
|
Bryn Haskell
(Nicolaus Copernicus Astronomical Center, Warsaw)
|
MULTIMESSENGER SEMINAR SERIES: Probing superfluid neutron star dynamics in the gravitational wave era. |
ABSTRACT: Neutron stars are one of the most exotic nuclear physics
laboratories in the universe. Not only are their interior densities
higher than nuclear saturation density, but their Fermi energies are
also high compared to thermal energy. They are thus 'cold' objects and
allow us to study fundamental physics in a completely different regime
than in terrestrial experiments. But this also means that neutron star
interiors are superfluid.
Superfluidity profoundly alters the dynamics of the system, by allowing
for extra degrees of freedom and large scale condensates that can flow
relative to the `normal' component if the star. Pulsar glitches, sudden
spin ups observed in radio pulsars, are an extraordinary macroscopic
manifestation of superfluidity at the microscopic scale. However
superfluidity also plays a role in many gravitational wave emission
mechanisms, such as the r-mode instability in rotating neutron stars.
In this talk I will discuss both the theoretical and observational
efforts of my group, which aim on the one side to bridge the gap in
scales between microscopic modelling of neutron superfluids and large
scale modelling of the star, and on the other to combine multi-messenger
observations in the X-ray, radio and gravitational waves, to constrain
fundamental physics at high densities. In particular I will focus on
models of pulsar glitches and of continuous gravitational wave emission
from accreting neutron stars. |
Sep 18 2018
14:00 |
room 128-129
|
Mario Spera
(Innsbruck University)
|
MULTIMESSENGER SEMINAR SERIES: tba |
ABSTRACT: tba |
Sep 13 2018
15:00 |
room 128-129
|
Albino Perego
(INFN Milano Bicocca)
|
MULTIMESSENGER SEMINAR SERIES: Multimessenger and neutrino astrophysics in the gravitational wave detector era |
ABSTRACT: The recent detections of gravitational waves (GWs) from coalescing binary black holes have opened a new window on the Universe. In addition, the first combined detection of GWs and photons from merging binary neutron stars has revealed the power of multimessenger astrophysics, confirmed intuitions coming from years of intense researches, and opened a new series nof urgent questions. Collapsing stellar cores and merging compact binaries are among the primary targets for the present generation of GW detectors and for their electromagnetic follow-up campaigns. In additions to GWs, the hot and dense matter involved in this kind of events emits copious amounts of neutrinos and photons. Moreover, matter expelled during these processes produces heavy elements and enriches the chemical composition of the host galaxies. The large amount of diverse, but related signals, in addition to their key role in the evolution of the Universe, qualifies their scenarios as the prototypical events of the multimessenger astrophysics led by GW detections. In this talk, I will review some of the most recent results concerning the emission of GWs, neutrinos, photons, and nucleosynthetic yields from core-collapse supernovae and binary neutron star mergers. I will mainly focus on the role of neutrinos and I will show how these elusive particles are key to shape the multimessenger picture of these events. |
Sep 06 2018
10:00 |
room 128-129
|
Lara Nava
(SISSA)
|
MULTIMESSENGER SEMINAR SERIES: Fundamental questions in High-Energy Astrophysics: a Multi-Messenger approach |
ABSTRACT: The study of some of the most fundamental open questions in High-Energy
Astrophysics can now take advantage of a multi-messenger investigation,
i.e. an approach based on merging information from different
observational 'channels', such as radiation, neutrinos, gravitational
waves and cosmic-rays. Efforts in this direction started decades ago, as
soon as detections of astrophysical neutrinos and cosmic rays became
available, but the number of topics and sources that could be studied
throughout complementary channels was very limited. The situation
drastically changed few years ago, thanks to the first detections of
gravitational waves and high-energy neutrinos, marking the birth of the
Multi-Messenger Era.
In this talk, I will first discuss what are the advantages and
limitations of each messenger and how the global understanding of an
astrophysical phenomenon can benefit from the simultaneous use of
different messengers.
I will then focus on some of the most relevant open issues in
High-Energy Astrophysics, and show how a multi-messenger approach is
allowing us to progress in our understanding of the underlying Physics.
I will discuss in particular i) the origin of Cosmic-Rays, ii) the PeV
neutrino background, and iii) the nature and properties of relativistic
jets. The common theme relating all these apparently different topics is
how and where the most energetic particles in the Universe are
accelerated, what is the role of magnetic fields, and how these two
fundamental ingredients interact and affect each other. |
Sep 06 2018
11:00 |
room 128-129
|
Sara Buson
(NASA-Goddard Space Flight Center / USRA and University of Wrzburg)
|
MULTIMESSENGER SEMINAR SERIES: New roadmaps throughout our Universe |
ABSTRACT: Everything we have known about the Universe, we have learned by studying thernlight. In the past decade, the advent of a new generation of space- and ground-based observatories, such as the Fermi Gamma-ray Space Telescope and Cherenkov instruments, has provided a huge boost in our understanding of the most energetic and violent phenomena that characterise the extreme cosmo.rnUnderstanding such phenomena can be exceptionally rewarding as they provide us with an indirect way to test physics conditions inaccessible to any human-atteinned Earth laboratory. Undoubtedly, the astrophysics field reveal itself as a secure land for panchromatic discoveries and, mostly, opens an exciting window into new opportunities and unprecedented perspectives. In fact, since very recently, we have now two new senses tornmap the Universe and tackle particle physics: we have just started hearing at gravitational waves and detecting the elusive cosmic neutrinos. I will explore how deciphering and combining the information carried byrnthe different messengers are the keys to peek through many different veils of our Universe. |
Jun 26 2018
14:00 |
Room 135
|
Akshay Rana
(Department of Physics and Astrophysics, University of Delhi, India)
|
Novel ways to constrain Graviton mass and spatial curvature |
ABSTRACT: In cosmology, it always remains a topic of great interest to constrain cosmological parameters
by using different approaches and observational probes to confirm their consistency. In the same
direction, I will present two novel ways that can be used to limit the mass of the Graviton and the spatial
curvature of the space. My talk will be focused on two different aspects of present precision cosmology,
1) Firstly, I will discuss about the graviton, which is a massless particle in GR while considered to be
massive in some alternative models of GR like; Massive gravity theories. I will present a novel
approach that can be used to put stringent constraints on its mass using galaxy clusters.
2) Similarly, the estimation of spatial curvature of the Universe is also one of the most fundamental
issue of modern cosmology. I will discuss a model independent approach to test the curvature of
space by using statistical features of strong gravitational lensing. |
May 22 2018
14:00 |
Room 135
|
Marco Baldi
(Bologna University)
|
Testing Cosmic Degeneracies with the SIMCODE project |
ABSTRACT: The upcoming era of precision cosmology, with several major observational enterprises expected to survey the Universe with unprecedented accuracy, will have the power to unveil even extremely feeble indications of possible new physics beyond the standard models of particle physics and cosmology.
Many crucial aspects of our present understanding of fundamental physics, such as the laws of gravity, the nature of dark matter particles, the mass spectrum of neutrinos, or the driving mechanisms of inflation, will be tested and constrained with a level of precision that will allow us to rule out vast portions of our current landscape of alternative theories and hypotheses. Nonetheless, a serious potential source of systematics in such long-term observational program has been so far mostly overlooked, and may undermine the real discriminating power of future observations. This amounts to the possibility that different extensions of the standard model may co-exist and their observational footprints may partially interfere with each other, or even compensate or completely cancel. Such situation, known as a Cosmic Degeneracy, could significantly bias if not properly
taken into account the interpretation of cosmological observations, and will in any case significantly reduce the real constraining power of future experiments. In this talk I will provide an overview of the present activities of SIMCODE, a multi-year computational cosmology project aimed at testing the effects of various types of Cosmic Degeneracies on cosmological observables by means of detailed combined simulations of structure formation. |
Apr 24 2018
14:00 |
Room 135
|
Luciano Rezzolla
(Frankfurt University)
|
Binary neutron stars: Einstein's richest laboratory |
ABSTRACT: I will argue that if black holes represent one the most fascinating
implications of Einstein's theory of gravity, neutron stars in binary system
are arguably its richest laboratory, where gravity blends with astrophysics
and particle physics. I will discuss the rapid recent progress made in
modelling these systems and show how the inspiral and merger of a binary
system of neutron stars is more than a strong source of gravitational waves.
Indeed, while the gravitational signal can provide tight constraints on the
equation of state for matter at nuclear densities, the formation of a
black-hole--torus system can explain much of the phenomenology of short
gamma-ray bursts, while the the ejection of matter during the merger can
shed light on the chemical enrichment of the universe. |
Apr 17 2018
16:00 |
Room 135
|
Margherita Talia
(Universita' di Bologna)
|
ALMA view of a massive spheroid progenitor: a compact rotating core of molecular gas in an AGN host at z=2.226 |
ABSTRACT: Massive star-forming galaxies with centrally
concentrated luminosity profiles at z>2 have been
suggested to be the direct progenitors of compact
quiescent galaxies (cQGs) at z=1.5-3. Some works have
been very recently published on the properties of the
ionized gas, dust continuum and X-ray emission of
samples of compact star-forming galaxies. However,
until now there are only a few sources that have been
spatially resolved with ALMA. This kind of
observations allow not only the study of the general
properties of the molecular gas, like density and gas
depletion time-scale, but also the measurement of its
size and the study of its kinematic, that are
fundamental information to understand the evolution of
cQGs progenitors.
I will present ALMA observations of GMASS 0953, a
candidate progenitor of cQGs at z=2.226. We measure
for the first time the size of the dust and molecular
gas emission of GMASS 0953 that we find to be
extremely compact (∼1 kpc). This result, coupled
with a very high ISM density (log(n)∼5.5 cm−3), a
low gas mass fraction (∼0.2) and a short gas
depletion timescale (∼150 Myr) imply that GMASS 0953
is experiencing an episode of intense star-formation
in its central region that will rapidly exhaust its
gas reservoirs, likely aided by AGN-induced feedback.
We are therefore witnessing in this galaxy the rare
and short-lived phase immediately before
star-formation quenching.
Kinematic analysis of the CO(6-5) line shows evidence
of rapidly-rotating gas (Vrot=320 km/s), as observed
also in a handful of similar sources at the same
redshift. On-going quenching mechanisms could either
destroy the rotation or leave it intact leading the
galaxy to evolve into a rotating quiescent galaxy. |
Feb 13 2018
14:00 |
Room 135
|
Alessandro Saro
(INAF OATs)
|
|
ABSTRACT: |
Jan 25 2018
14:00 |
Room 135
|
Sergio Hernandez Cadena
(Universidad Nacional Autonoma de Mexico (UNAM))
|
Dark Matter searches with the HAWC Observatory |
ABSTRACT: The High Altitude Water Cherenkov (HAWC) observatory is a wide-field-of-view\r\n(2sr) and high duty cycle (> 95%) gamma-ray\r\n detector which operates at an altitude of 4100 m in the state of Puebla,\r\nMexico. HAWC performs indirect Dark Matter searches by det\r\necting high energy photons (E > 1TeV) resulting from annihilation or decay\r\nof WIMPs. Since HAWC continuously surveys the sky, we investigated several\r\ntargets as dSph galaxies, dwarf irregular galaxies, and the Virgo Cluster.\r\nAlthough HAWC has not seen statistically significant excess from this\r\nsources, we will present the annihilation cross-section and decay lifetime\r\nlimits (95% CL) for WIMP masses from 1 to 100 TeV. |
Jan 09 2018
14:00 |
Room 135
|
Santi Cassisi
(Teramo Observatory)
|
On the Multiple Stellar Populations Phenomenon in Galactic Globular Clusters: What do we really know? |
ABSTRACT: |
Dec 19 2017
14:00 |
Room 135
|
Vincenzo Galluzzi
(INAF Bologna)
|
Multi-frequency and multi-epoch polarimetry of a complete sample of PACO radio sources |
ABSTRACT: The high-frequency (> 20 GHz) bright flux density (> 200 mJy at 20 GHz)
radio population is dominated by blazars but their polarization properties
are still poorly constrained: the latter are informative about magnetic
fields and plasma in inner regions of relativistic jets. Cosmologically,
extragalactic radio sources are an important contaminant to the CMB at
scales smaller than 30' up to ~ 100 GHz, hence crucial in the search for
primordial B-modes. We present the results of ALMA 100 GHz polarimetric
observations of 32 radio sources, selected as a complete subsample of 104
sources already observed with high sensitivity (~ 0.6 mJy) in 7 frequency
bands (1.1-39 GHz) with ATCA. We confirmed polarization spectra of single
sources cannot be simply inferred from total intensity ones, as different
source components dominate the different emissions; we find complex
behaviours in polarization fractions and polarization position angles
(PPAs). Moreover, the observations are useful to assess statistical and
systematic accuracies of PPA obtained with ALMA and to explore its use for
calibrating CMB experiments. Dedicated analysis of few peculiar objects in
our sample will be also shown. |
Nov 28 2017
14:00 |
Room 135
|
Francesca Pozzi
(Bologna University)
|
Are the bulk of Herschel sources protoshperoids? |
ABSTRACT: Infrared wavelengths hold the key to understanding the evolution of
galaxies. Thanks to unprecedented depth and the crucial wavelength range of
the Herschel mission, a much better census of the dust-obscured
star-forming galaxies has been obtained. Together with the Herschel IR luminosity function of galaxies and
AGN up to z~4, I will present a backward approach for his interpretation
and I will show how, the bulk of Herschel sources at z>2 can be explained
as progenitors of local spheroids caught during their formation. |
Nov 14 2017
14:00 |
Room 135
|
Isabella Prandoni
(INAF-IRA)
|
Galaxy/AGN co-evolution: what can we learn from deep radio continuum surveys |
ABSTRACT: A complete the census of AGN activity, especially at redshifts where most of the accretion occurred, is essential to understand the physical link between supermassive black-holes (SMBH) and galaxies, and their cosmic co-evolution. In particular we need to identify the contribution of obscured accretion activity in bolometric surveys and quantify its impact on the evolution of star formation.
The galaxy populations probed by radio-continuum surveys change dramatically reaching sub-mJy and microJy flux densities. While the bright radio sky is largely dominated by radio-loud (RL) AGN, at sub-mJy flux densities the contribution from star-forming galaxies (SFG) becomes increasingly important. In addition, recent multi-wavelength studies have revealed the presence of a third population of sources at 10-100 microJy (uJy) levels, the so-called radio-quiet (RQ) AGN, i.e. AGN that do not present the typical large-scale radio morphology (jets and lobes), but show signs of AGN activity at optical/IR or X-ray wavelengths. This finding has opened new exciting perspectives for deep radio-continuum surveys, as they can provide
a unique and powerful dust/gas-obscuration-free tool to get a global census of both star formation and AGN activity up to high redshifts. It is worth to note that the origin of the radio emission in RQ AGN is hotly debated. It can originate from star formation, AGN activity or, more likely, from a combination of the two processes. Identifying the process(es) responsible for the radio emission in these systems can shed light on the nature of the feedback mechanisms at work in RQ AGN and on their role in shaping galaxies.
In the lead-up to the SKA, several radio-continuum legacy surveys are
ongoing at new radio telescopes and upgrades, including eMERLIN (UK), JVLA (USA) and LOFAR (The Netherlands). In particular deep observations of well-known extra-galactic fields with dense multi-band coverage are being exploited to improve our knowledge of the high-redshift Universe from a radio perspective, and to observationally address the star formation history and the role of AGN in galaxy evolution. These surveys represent natural test-beds for the science that will be delivered by the SKA and its precursors (ASKAP, MWA and MeerKAT) in the near future on larger statistical basis, and are providing important information to fine-tune science cases, observing strategies and telescope designs.
I will discuss our current understanding of the faint radio sky, focussing on recent results coming from extensive multi-band analysis of two extragalactic deep fields: a) the Lockman Hole (LH) region observed at 150 MHz, 350 MHz and 1.4 GHz with LOFAR and WSRT; b) the GOODS-N field observed with eMERLIN and JVLA at 1.4 and 5 GHz.
The LH provides an excellent test-bed for the radio-continuum all-sky survey planned at ASKAP and SKA-LOW, as it is characterized by similar
sensitivities and spatial resolutions. The source statistics available in this field (covering up to 30 sq. degrees at 150 MHz) is large enough to provide robust observational constraints for both the SFG and RQ AGN
populations, and allows us to disentangle among different evolutionary
models proposed for SFG.
On the other hand, thanks to the unique combination of sensitivity (sub-uJy) and angular resolution (~0.1 arcsec) provided by combined eMERLIN/JVLA observations, the GOODS-N field can be used as a proxy for future SKA-MID deep surveys, and is particularly well suited to address the issue of the origin of radio emission in RQ AGNs. |
Nov 13 2017
14:00 |
T.B.A.
|
Umberto Maio
(INAF Ts)
|
The first billion years |
ABSTRACT: A theoretical framework to understand the formation of the first
galaxies and massive black holes at early times (z>6) will be discussed. The
role of different initial mass functions (IMFs) and spectral energy
distributions (SEDs) assumed for primordial star formation episodes as well
as the build-up of a cosmic ionizing radiation leading the re-ionization
epoch will be outlined. Our results point towards a minor role of mergers in
the formation and evolution of early baryonic structures and highlight the
need to account for hydro and radiative transfer (RT) effects in a more
detailed way. The imprints left by primordial metal spreading on the CMB
(via distorsions due to e.g. CII, OI, SiII, FeII fine-structure transitions)
and on the metal abundance ratios of DLA and GRB-host observables will be
quantified and compared against available observational data. |
Nov 07 2017
14:00 |
Room 135
|
Vincent Pelgrims
(LPSC, Grenoble, France)
|
Cosmic anisotropies from quasars |
ABSTRACT: Large-scale correlations of the polarization vectors of the light form quasars were discovered almost twenty years ago. These correlations take place over giga parsec scale distances. Due to their extreme-scale nature these observations have been recognized as potentially competing the isotropy of the well-accepted concordance cosmological model. Later these observations have been confirmed and the correlation signal enhanced by means of additional data. After a review of the main features of those large-scale polarization alignments, I shall present the related results that I obtained. Therefore, I shall address two types of unexpected, but observed, correlations that involve the orientation of the linear polarization vectors of the light of quasars, at optical and radio wavelengths. First, the quasar polarization vectors appear to be coherently oriented to one another over very large scales and, second, their orientations are found to be correlated with specific directions defined by the quasar spatial distribution. I will discuss a tentative interpretation of the data following which the polarization correlations reflect the coevolution of the black hole spin axes with and within the cosmic web. |
Oct 24 2017
14:00 |
Room 135
|
Mattia Negrello
(Cardiff University)
|
Dust-obscured galaxies under the cosmic zoom lens in the Herschel-ATLAS |
ABSTRACT: The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is the\r\nwidest-area extragalactic survey undertaken with the Herschel space\r\nobservatory, covering around 600 square degrees of the sky from far-infrared\r\nto sub-millimetre wavelengths. One of its scientific goals is the systematic\r\nsearch of gravitationally lensed dust-obscured galaxies using a simple and\r\nefficient method that was first proposed in the 90s, which exploits the\r\nsteep number counts of sub-mm selected galaxies.\r\nAfter discussing the importance of gravitational lensing in the study of\r\ndistant galaxies and the key role played by dust-obscured galaxies in our\r\nunderstanding of galaxy formation and evolution, I will review the status of\r\nthe search of lensed galaxies in H-ATLAS and of the associated campaign of\r\nfollow-up multi-wavelength observations. \r\nI will then describe the technique we use to reconstruct the intrinsic\r\nmorphology of the background galaxies from the observed lensed images and I\r\nwill show its application to both imaging and interferometric data.\r\nThe talk is meant for a wide audience so please come along even if you are\r\nnot very familiar with far-infrared/sub-mm astronomy and/or gravitational\r\nlensing. |
Oct 17 2017
14:00 |
Room 135
|
Paolo Padovani
(ESO)
|
Active Galactic Nuclei: whats in a name? |
ABSTRACT: AGN are quite unique astronomical sources that cover the full
electromagnetic spectrum over more than twenty orders of magnitude in
frequency, with different bands providing windows on the physics of
different sub-structures. They come in a large number of flavours
only partially related to intrinsic differences. I will highlight the types
of sources selected in different bands, the relevant selection effects and
biases, and the underlying physical processes. I will then look at the ``big
picture'' by describing the most important parameters one needs to describe
the variety of AGN classes and by discussing AGN at all frequencies.
I will conclude with a look at the most pressing open issues and the main
new facilities,
which will flood us with new data to tackle them. The talk is based on a
recent review
paper I have published in Astronomy and Astrophysics Review and should be
useful to
all astronomers, irrespective of their field of research. |
Oct 12 2017
11:30 |
Room 131
|
Filippo Fraternali
(Universita' di Bologna)
|
The galactic gas cycle: understanding the interface between galaxies and the circumgalactic medium |
ABSTRACT: |
Oct 03 2017
14:00 |
Room 135
|
Roberto Gilli
(Universita' di Bologna)
|
The physics, environment and evolution of early supermassive black holes |
ABSTRACT: Bright quasars at z>6 are powered by black holes that grew up to a few
billions solar masses within the first billion years of the
Universe. Theory struggles to explain how these extreme systems have
formed and grown, and is making several - yet untested - predictions
since 15 years.
I will report on some recent observational programs designed at
studying the physics, environment and cosmological evolution of AGN at
very high redshift. These include: i) observations of large-scale
galaxy overdensities around z~6 quasars; ii) measurements of the
luminosity function of z>3 AGN based on major deep multi-band surveys
such as the CDFS and COSMOS.
Prospects will be finally presented for expanding these programs and
for future mission developments, that may eventually constrain models
of early black hole formation. |
Sep 12 2017
11:30 |
Room 135
|
Shreya Banerjee
(Tata Institute of Fundamental Research, Mumbai, India)
|
How do Inflationary Perturbations become Classical? |
ABSTRACT: I shall revisit one recently proposed working model of classicalization by rnspontaneous collapse, known as Continuous Spontaneous Localization (CSL), rnto look for possible modifications to scalar and tensor power spectra for rncanonical single field slow-roll inflation and their implications. rnI shall show that it can potentially change the consistency relation of rnsingle-field models and a precise measurement of tensor spectral tilt nt rnand its running could serve as a test of such dynamics in the early universe.rnIn the later part of my talk, I shall discuss about the application of the rncollapse dynamics to the more generalized non-canonical k-inflationaryrn scenario and try to quantify the effects of collapse on inflationary rndynamics, hence compare the results from both the approaches. rnWe observe in this study that the observables from the scalar sector, i.e. rnscalar tilt ns, running of scalar tilt αs and running of running of scalar rntilt βs, can not potentially distinguish a collapse modified inflationary rndynamics in the realm of canonical scalar field and k−inflationary scenarios. rnThe only distinguishable imprint of collapse mechanism lies in the observables rnof tensor sector in the form of modified consistency relation and arn blue-tilted tensor spectrum only when the collapse parameter δ is non-zerorn and positive.rnLastly, I shall talk about plausible other approaches by which one can try rnto investigate the quantumness of primordial cosmological fluctuations rnand look for the effect of CSL on these approaches. |
Sep 05 2017
14:00 |
Room 135
|
Radek Stompor
(APC, Paris)
|
Data Analysis for future CMB experiments |
ABSTRACT: |
Jun 20 2017
14:00 |
Room 135
|
F. Buitrago
(University of Lisbon)
|
PRESSING AND PENDING QUESTIONS ABOUT MASSIVE GALAXIES |
ABSTRACT: The devil is in the details, and so it is for our fully understanding of the development of the most massive galaxies of the Universe. Massive (M_stellar > 10^11 M_Sun) and compact (effective radius < 1-1.5 kpc) galaxies are ubiquitous at z > 1.5 but they are very scarce in our nearby Universe. To explain this "disappearance" current evidence suggests a passive evolution dominated by minor merging, although there is also room for a series of observational biases. What have happened in reality? How do massive galaxies change their sizes and morphologies through cosmic time? Does the environment have a say about it? Do all massive galaxies end up their lives as huge early-type galaxies? I will review the state-of-the art about these topics, and the insights we are gaining by investigating the unmatched environmental determination that the GAMA survey is providing us. However, I will focus on our last Hubble Ultra Deep Field study where we have explored galaxy surface brightness profiles down to 30 mag arcsec^-2 for the few massive galaxies in the foreground of the image.
Merging is undoubtedly taking place for these massive galaxies,
progressively building a stellar envelope (stellar halo) around them and
therefore explaining their size and morphological evolution. These galaxy haloes store 3.5% of the galaxy stellar mass at z=2, while this ratio grows up to 28.7% at z=0.1. |
Jun 15 2017
14:00 |
Room 135
|
Zeljka Bosnjak
(University of Zagreb)
|
Radiation modelling of the GRB emission |
ABSTRACT: We have developed a time-dependent numerical model to calculate the prompt gamma-ray burst emission over a broad energy range (from soft X-ray to GeV energies). For a given relativistic ejection by the central source, we compute the properties of the internal shock phase of the relativistic jet. This dynamical model is coupled to a radiative code to compute the non-thermal emission of each emitting region. I will present a comprehensive set of simulations of GRB spectral evolution and the impact of model parameters related to shock physics and to the initial conditions in the ejecta. The predictions of the model are confronted with GRB observations in the standard sub-MeV energy range as well as with the high energy bands observed by Fermi/LAT. I will also address several issues related to observing prompt GRB emission with the Cherenkov Telescope Array (CTA). |
Jun 14 2017
14:00 |
TBA
|
Adriana de Lorenzo
(Universidad Nacional Autnoma de Mxico, Instituto de Astronoma)
|
Evolution of barred galaxies: the formation of double bars and the debate about bar stability |
ABSTRACT: The general picture of galaxy formation and evolution includes bars as the
main drivers of internal secular processes affecting the lifetime of disc
galaxies. However, there are many open questions about **bar evolution**
that we need to answer before we understand the role of bars in **galaxy
evolution**. Are bars long-lived systems? is a major example but not the
only one.
Particularly interesting is the case of double-barred galaxies: at least 20%
of all spirals have turned out to host not only one but two bars embedded in
them. The processes inducing the formation of these systems represent a
challenge for all the numerical simulations and are still under discussion.
All the theoretical hypothesis on the formation and evolution of
double-barred galaxies have not been tested due to the lack of observational
works focused on these systems. I will present the results obtained from a
spectroscopic survey of double-barred galaxies that we are combining with a
thorough photometric analysis of their components. The observational
evidences will be discussed in the framework of the double bars formation
and evolution theories. |
May 03 2017
14:00 |
Room 135
|
Suchita Kulkarni
(Institute of High Energy Physics, Vienna)
|
Informal seminar: "Dark matter signals with long lived mediators" |
ABSTRACT: Indirect detection of dark matter is an important probe to hunt for particlernnature of dark matter. The searches are sensitive to underlying particlernphysics model as well as the dark matter density distribution e.g. at therncentre of galaxy. I explore indirect detection prospects for scenarios wherernDM particles annihilate into long lived mediators via t-channel. Thesernscenarios are of an interest for explaining AMS excess as well as canrnprovide a complementary probe for boosted dark matter scenarios. I willrndiscuss the formalism for computing the flux and anisotropies for decays ofrnlong-lived mediators into SM final states. Finally, I will consider thernimpact dark matter density enhancement at the centre of galaxy on thesernanisotropies. I will also comment on the feasibility of obtaining largerndensity enhancement which can impact signatures at indirect detection. |
Apr 18 2017
14:00 |
Room 135
|
Andrew Jaffe
(Imperial College, London)
|
Bayesian Hierarchical Models for weak lensing analysis |
ABSTRACT: TBA |
Apr 11 2017
14:00 |
Room 135
|
Lidia Tasca
(LAM , Marseille)
|
Galaxies in formation: the assembly of massive galaxies at 2 < z < 5+ |
ABSTRACT: I will discuss the main properties of bright and massive star-forming galaxies as seen around their peak of star formation, including
when galaxies of different masses start forming stars. I will put the accent on the physical processes which shape galaxies along
cosmic time.
Our data are drawn from the VIMOS Ultra Deep Survey (VUDS) which assembled the largest spectroscopic sample to date of star forming galaxies at 2
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Mar 16 2017
14:00 |
Room 135
|
Ben Metcalf
(University of Bologna, Department of Astronomy,)
|
The Future of Strong Gravitational Lensing |
ABSTRACT: |
Jun 09 2015
14:00 |
SISSA, Room 135
|
Ilia Musco
(CNRS Postdoctoral Fellow, Observatoire de Paris)
|
Quasi-Static Solutions for Compact Objects in Chameleon Models |
ABSTRACT: It has been suggested that a scalar field φ non-minimally coupled
to matter could be responsible for the observed accelerated expansion of the
Universe. However, the fact that we are able to measure its effect only on
cosmological scales but not on local ones, such as that of our solar system,
might be the consequence of a screening mechanism. This is the essence of
the Chameleon model. Understanding its viability requires solving the field equations in the transition regime where the scalar field transitions from a region of high density to the outer region where it plays the role of the Dark Energy. In this work we analyze quasi-static spherically symmetric solutions for compact objects solving the Tolman-Oppenheimer-Volkoff equations coupled with the Klein-Gordon equation in a quasi static regime that takes into account the background expansion without needing to introduce an artificial cosmic matter corresponding to a non-spatially flat metric. |
Jun 03 2015
14:00 |
Tba
|
Sumit Kumar
(Centre for Theoretical Physics, New Delhi)
|
Models of accelerating Universe and their observational status |
ABSTRACT: To explain different theoretical problems in standard model of cosmology as well as to explain some observational facts, we need two phases of accelerated expansion in the cosmological history of universe. One is inflationary epoch which happened very early in the Universe and other is more recent phenomenon explained by dark energy. We will discuss some theoretical as well as observational issues regarding these two accelerating phases of the Universe. We shall discuss a specific two brane warped geometry model in which brane separation stabilizes and at the same time it gives inflation on visible brane which is consistent with the present data. We shall also discuss an interacting dark energy model and clustering GCG in light of the observational data. Finally, I shall also introduce a python package ScalPy for studying late time scalar field cosmology. |
May 27 2015
14:00 |
SISSA, Room 135
|
Suvodip Mukherjiee
(IUCAA - Pune, India)
|
Hemispherical Asymmetry and Power Suppression in Cosmic Microwave Background |
ABSTRACT: The recent measurements of temperature and polarization of Cosmic Microwave Background (CMB) have improved our understanding of the Universe and have showed a remarkable agreement with the ΛCDM cosmological model. However, scale dependent features like power suppression in the angular power spectrum, hemispherical asymmetry in the temperature field of CMB and direction dependent spectral index, indicate possible departure from the ΛCDM model persist in the CMB data. Speaker will discuss a mechanism linked to possible initial inhomogeneities in the inflationary scalar field that could explain all these observed phenomena. Initial inhomogeneities lead to non-zero values of anisotropic inflationary parameters, which at leading order cause different amounts of hemispherical asymmetry in the scalar and tensor perturbations. The second order effect of anisotropic inflationary parameters naturally lead to a suppression (enhancement) of power at low multipole l for scalar (tensor) perturbations. As a result this model unifies both the large angular scale features like suppression of power and hemispherical asymmetry by a single phenomenon. The salient feature of this model is that it produces all the effects in tensor and scalar perturbations by just two independent parameters and future missions can measure these parameters uniquely and hence the validity of the model can be investigated. |
May 21 2015
14:00 |
SISSA, Room 135
|
Domenico Marinucci
(Roma Tor Vergata)
|
Needlet Methods for Cosmological Data Analysis: from the Sphere to the 3-Dimensional Case |
ABSTRACT: In this talk, we will start from a review of the construction of spherical needlets, a form of spherical wavelets characterized by a number of important properties for Cosmological data analysis. We shall discuss their statistical and analytic properties, and then we shall review a number of recent and less recent applications, focussing in particular on the search for nonGaussianity and asymmetries in Cosmic Microwave Background data. We will then consider extensions to three-dimensional settings, reviewing in particular the recent proposal of 3d radial needlets and their potential applications to future Large Scale Structure surveys. |
May 14 2015
16:00 |
SISSA, Room 135
|
Carmelita Carbone
(DARKLIGHT postdoc at INAF-Astronomical Observarory of Brera)
|
Clustering, lensing, and ISW-RS from the DEMNUni neutrino simulations. |
ABSTRACT: I will present the first set of cosmological simulations produced within the Dark Energy and Massive Neutrino Universe (DEMNUni) project. These
simulations are characterized by L=2 Gpc/h, Npart=2 x 2048^3, a baseline
LCDM-Planck cosmology, and four different total neutrino masses, Mnu=0,
0.17, 0.3, 0.53 eV, with a degenerate mass spectrum. They are the largest N-body simulations to date with a massive neutrino component treated as an additional particle type. I will present fully non-linear effects in the presence of massive neutrinos, extracted from the DEMNUni simulations, and show how neutrino free-streaming alters not only LSS clustering and lensing, but introduces also an excess of power in the ISW/RS signals, and related cross-correlations, at intermediate scales. |
Mar 10 2015
14:00 |
SISSA, Room 135
|
Albert Bosma
(Laboratoire d'Astrophysique de Marseille)
|
Dark Matter in Galaxies |
ABSTRACT: I will give an historical overview on how the Dark Matter problem
developed, with emphasis on rotation curve studies. In doing so, I
will point out several misconceptions which are have arisen over the
years, and can still be found in some accounts. I will also discuss
briefly the current situation and address future plans with new
surveys to be done with yet to be constructed radiotelescopes. |
Sep 23 2014
16:00 |
Meeting Room - 7th Floor
|
Carlo Baccigalupi
(SISSA)
|
Recent Planck polarization results and implications for ongoing CMB observations |
ABSTRACT: |
Jan 08 2014
14:00 |
SISSA, Room 135
|
Silvio Bonometto
(INAF-Trieste)
|
Strongly coupled CDM-DE, plus WDM. The LCDM crisis overcome? |
ABSTRACT: Above a suitable coupling, at high z CDM and DE (a scalar field) settle on a kinetic tracker solution, with steadily fixed proportions of radiation, CDM, DE and, possibly, a WDM component. When WDM derelativizes, the model naturally evolves towards a cosmology with density parameters and CMB spectra almost identical to LCDM. However: (i) DM particles are mostly in the range 0.1-0.4 keV, so probably easing the core profile problem; (ii) fluctuation spectra, almost identical to LCDM down to the galactic scale, exhibit a gap on the MW satellite scale to regain power at still lower scales; (iii) the formation of early BH is facilitated and the first stars are likely to arise earlier. |
Oct 10 2013
14:00 |
SISSA, Room 135
|
Lingfei Wang
(Physics Department, Lancaster University, UK)
|
A new mechanism for curvature perturbations |
ABSTRACT: I will explain the spectator scenario and show its advantages compared to the curvaton scenario, under the latest Planck constraints. The spectator scenario generates a smaller non-Gaussianity, negligible isocurvature perturbations, and less tuning. It agrees well with the current Planck data in the visible sector inflation setup, as an example. It also explains the CMB dipole asymmetry with a brief fast roll phase. I will close the talk by proposing the CMB power multipoles, as an alternative approach independent of the CMB dipole asymmetry model |
Jun 20 2013
10:00 |
Room 135
|
Gianluca Castignani
(SISSA)
|
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ABSTRACT: |
Jun 20 2013
11:00 |
Room 135
|
Jing Tang
(SISSA)
|
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ABSTRACT: |
Jun 05 2013
14:00 |
Room 135
|
Yang Chen
(SISSA)
|
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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=8825 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. |
