September 30, 2015 | 3:00 PM | ERC 161 | Astronomy Colloquium Timing of Exoplanets: the Big, the Small, the Circumbinary Dan Fabrycky, The University of Chicago
PDF Since the beginning of the exoplanet era, the reality of planets was confirmed and their properties mapped out by their time-variable signals. From the first pulsar-timing system, PSR 1257+12, to the dynamically precessing Doppler system, GJ 876, some of the first examples of multi-planet systems were confirmed via Newtonian interactions among the planets. This business has gone industrial using the 4-year stare of the Kepler mission, with which we used transit timing variations to map out the mutual orbital perturbations, confirm systems of planets by the dozens and elucidating the class of sub-Neptune planets. Now we are using transit timing to determine masses and architectures of systems of temperate Jupiters, determine the eccentricity scale of terrestrial planets, and detect and measure masses of planets orbiting around short-period binary stars. While the dynamical calmness of this new crop of exoplanets is comparable to the Solar System, other aspects seem as weird as ever, a continued forcing function on planet formation theory. Image Credit: NASA / Tim Pyle
October 21, 2015 | 3:00 PM | ERC 161 | Astronomy Colloquium The Continuing Mystery of the Anomalous Microwave Emission Bruce T. Draine, Princeton University
"Anomalous Microwave Emission" (AME) refers to dust-correlated emission in the 15-50 GHz frequency range that is far stronger than had been expected from the low-frequency "tail" of the thermal infrared emission from dust grains at ~20K. Discovered in the course of CMB studies, it presents a significant "foreground" that CMB observers would like to remove. In 1998 it was proposed that the AME was rotational emission from ultrasmall dust grains with rotational frequencies of 15-50 GHz. The population of polycyclic aromatic hydrocarbons (PAHs) responsible for strong infrared emission bands between 3.3 and 17um were natural candidates for the emitter. This "spinning dust" hypothesis appeared to be a very natural explanation for the AME, and was supported by upper limits on polarization of the AME. I will describe recent observational efforts to demonstrate a link between the AME and the PAHs. Surprisingly, the results do not support the conjectured AME-PAH linkage. Other possibilities for the source of the AME will be discussed. The figure shows the spectrum of a region in the Perseus molecular cloud with strong Anomalous Microwave Emission (Planck Collaboration et al 2011 Astronomy & Astrophysics 536, A20).
October 28, 2015 | 3:00 PM | ERC 401 | Wednesday colloquium The Future of Cosmological Physics: New Avenues Marc Kamionkowski, Johns Hopkins University
PDF We now have a highly successful cosmological model in place, but one which leaves many questions unanswered. What is the new physics responsible for primordial perturbations? What is the dark matter? What causes an accelerated cosmic expansion? And why is there a preponderance of matter over antimatter? New generations of galaxy surveys will continue to map the cosmic mass distribution on ever larger scales and with increased precision, while CMB experiments are beginning to map the polarization B modes from inflation and from lensing. It is never too soon, though, to think about what else can be done with these new experiments and in subsequent generations of experiments. In this talk I will discuss a variety of new early-Universe fossils that can be sought with galaxy surveys and discuss new ideas to probe primordial power on scales far smaller than those accessible with galaxy surveys.
November 4, 2015 | 3:00 PM | ERC 161 | Wednesday colloquium The formation and evolution of the galaxy population Simon White, Max Planck Institute for Astrophysics
PDF Recent observations of the high-redshift universe have characterized the initial conditions for nonlinear structure formation over the full range of scales responsible for dwarf and giant galaxies, galaxy clusters and the large-scale cosmic web. At the same time, wide-field spectroscopic and photometric surveys have measured the abundance and clustering of low-redshift galaxies as a function of mass, size, morphology, kinematic structure, gas content, metallicity, star formation rate and nuclear activity, while deep surveys have explored the evolution of several of these distributions to z>3. Galaxy population simulations aim to interpret these observations within the LCDM structure formation paradigm, thereby constraining the complex, diverse and heavily interconnected astrophysics of galaxy formation. Recent simulations are broadly consistent with the galaxy abundances and clustering seen in both wide-field and deep surveys, and provide predictions for topics as different as galaxy-galaxy lensing, the triggering and duty cycles of AGN, and the evolution of Tully-Fisher, mass-size and mass-metallicity relations. They show galaxy assembly histories to be strongly constrained by the structure formation paradigm, giving insight into issues such as internally versus externally driven evolution, inflow versus winds, major versus minor mergers, in situ versus ex situ star formation, and disks versus bulges. In addition, simulations can now be adapted to represent any chosen LCDM-like cosmology, allowing a first assessment of whether galaxy formation uncertainties will limit our ability to do precision cosmology with galaxy surveys.
November 11, 2015 | 3:00 PM | ERC 161 | Astronomy Colloquium Statistical mechanics of self-gravitating N-body systems Scott Tremaine, Institute for Advanced Study
PDF There have been many attempts to apply the powerful tools of statistical mechanics to self-gravitating N-body systems such as star clusters, galaxies, and planetary systems. I will describe why this is difficult, some notable failures and successes, and recent work on two arenas where these tools offer new insight: the distribution of young stars in the central parsec of our Galaxy, and the distribution of orbits of exoplanets.
December 2, 2015 | 3:00 PM | ERC 161 | Wednesday colloquium Planck, BICEP, and the Early Universe Raphael Flauger, The University of Texas at Austin
PDF The cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a brief introduction, I will discuss various aspects of the recently released Planck full mission data before turning to a discussion of string inspired models and the search for their signatures. Finally, I will turn to the search for primordial B-modes.
December 9, 2015 | 3:00 PM | ERC 161 | Astronomy Colloquium Numerical Simulations of Black Hole Accretion Ramesh Narayan, Harvard University
Accreting black holes are observed in a large variety of systems in astronomy: active galactic nuclei, X-ray binaries, tidal disruption events, gamma-ray bursts. While analytical one-dimensional models have been enormously useful for understanding several aspects of accretion physics, other aspects such as the formation of jets and winds are beyond the scope of such models. Numerical general relativistic MHD simulations are able to include more physics than analytical models and are proving increasingly useful for studying the multidimensional gas dynamics and radiative properties of accretion flows. The talk will review current progress in this field.
October 2, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Oscillations in the CMB bispectrum Moritz Munchmeyer, Institute d'Astrophysique Paris
Planck data is used to search for bispectrum oscillations.
Oscillating signatures in the correlation functions of the primordial density perturbations are predicted by a variety of inflationary models. A theoretical mechanism that has attracted much attention is a periodic shift symmetry as implemented in axion monodromy inflation. This symmetry leads to resonance non-gaussianities, whose key feature are logarithmically stretched oscillations. Oscillations are also a generic consequence of excited states during inflation and of sharp features in the potential. Oscillating shapes are therefore a very interesting experimental target.
After giving an overview of these motivations, I will discuss how to search for these signatures in the CMB. Fast oscillations are difficult to search for with traditional estimation techniques, and I will demonstrate how targeted expansions, that exploit the symmetry properties of the shapes, allow to circumvent these difficulties. As a member of the Planck collaboration, I will discuss the Planck results that have been obtained using these methods in the bispectrum, as well as a joint search using bispectrum and power spectrum. Due to their low overlap with other non-gaussian shapes, oscillating bispectrum shapes are not exhaustively constrained and a potential discovery is therefore not yet ruled out.
My talk will be based in particular on arxiv:1412.3461, arxiv:1505.05882 and Planck publications on inflation and non-gaussianities.
October 9, 2015 | 12:00 PM | ERC 401 | Friday noon seminar WIMP-Search Results from the Second CDMSlite Run Ritoban Basu Thakur, The University of Chicago
The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Results are presented from the second CDMSlite run with an exposure of 70 kg days, which reached an energy threshold for electron recoils as low as 56 eV. A fiducialization cut reduces backgrounds below those previously reported by CDMSlite. New parameter space for the WIMP-nucleon spin-independent cross section is excluded for WIMP masses between 1.6 and 5.5 GeV/c^2.
October 16, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Healthy solutions in the decoupling limit of quasi-dilaton theory Rampei Kimura, New York University
Quasidilaton massive gravity is an extension of massive General Relativity to a theory with additional scale invariance and approximate internal Galilean symmetry. In this talk, I will present a detailed study of the spherically symmetric solutions which are free of ghosts, tachyons, gradient instability, and superluminality for all propagating modes in a theory of quasidilaton.
October 23, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Combining Probes of Large-Scale Structure in the Precision Cosmology Era Elisabeth Krause, KIPAC, Stanford
Current and upcoming wide-field large-scale structure surveys, such as DES and LSST, will enable precision measurements of various observables of large-scale structure, such as weak lensing, galaxy clustering, and the abundance of galaxy clusters. These observables probe different aspects of cosmic structure formation, and combining them improves constraints on cosmology significantly. However, these observables probe the same underlying density field, and the information content is correlated. Additionally, they share correlated (astrophysical and observational) systematic effects. In this talk I will introduce the analysis concepts for the joint analysis of probes of large-scale structure currently under development for CosmoLike, a fast and self-consistent LSS likelihood analysis package. Using a simulated DES combined probes analysis as an example, I will discuss cross-correlations of observables, and modeling and mitigation of systematic uncertainties affecting multiple probes, and in particular give a quantitative comparison of different weak lensing systematics.
November 6, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Observing the transient sky with the highest energy multi-messengers Kumiko Kotera, Institut d'Astrophysique de Paris
Kumiko Kotera In the transient sky are found the most violent phenomena in the universe. The energy production and release of these events is mysterious. Very high energy messengers (photons, neutrinos and cosmic rays at energies >10^14 eV) offer a unique perspective to their study. Transients are indeed the best known sources capable of supplying enough energy and flux to astroparticles at the observed level. In this talk, we will focus on some of these powerful objects (young pulsars, millisecond pulsar systems, superluminous supernovae) and explore their capability to produce the highest energy particles, by building comprehensive scenarios of acceleration, escape and propagation. We will estimate the expected signatures of these scenarios, and compare them to the latest multi-wavelength and multi-messenger data, in order to constrain the source properties. In particular, the expected neutrino signatures will be a good target to be probed by the Giant Radio Array for Neutrino Detection (GRAND) project, that aims at detecting high-energy neutrinos with a 100'000 km2 radio antenna array in the Tianshan mountains in China.
November 13, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Superfluid Dark Matter Lasha Berezhiani, Princeton University
PDF I will talk about a novel theory of dark matter superfluidity that matches the success of LCDM model on cosmological scales while simultaneously reproducing the MOND phenomenology on galactic scales.
Image credit: NASA/CXC/SAO
November 20, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Lensing and Other Results from ACTPol Alexander van Engelen, Canadian Institute for Theroetical Astrophysics
Surveys of the CMB from ground-based observatories have revealed much about cosmology, in particular by measuring effects on CMB photons since recombination. In this talk, I will summarize results from the ongoing ACTPol survey, highlighting in particular the measurement of gravitational lensing by matter between us and the CMB recombination surface. I will discuss challenges with these measurements and also look forward to what will be possible with upcoming surveys such as SPT-3G, AdvACT, and CMB-S4.
December 4, 2015 | 12:00 PM | ERC 401 | Friday noon seminar Stellar Explosions, Strongly Lensed Steve Rodney, University of South Carolina
The Hubble Space Telescope Frontier Fields survey has been extending the reach of HST by targeting massive galaxy clusters that act as cosmic telescopes: using gravitational lensing to amplify the light of distant objects. This makes it possible to detect the explosions of stars that formed when the universe was less than a few billion years old. It also yields a small but special sample: highly magnified supernovae that serve as sensitive probes of the lensing cluster's dark matter potential. I will describe some of the recent discoveries from this program, including a highly magnified Type Ia supernova, a peculiar fast transient observed twice in a multiply-imaged galaxy, and an ancient supernova being multiply imaged by both a galaxy and a galaxy cluster. I will also look ahead to discuss how HST, JWST and WFIRST can help develop strongly-lensed supernovae into a powerful new tool for studying dark matter and dark energy in the next decade.
November 23, 2015 | 12:00 PM | ERC 401 | Special seminar X-Ray Emission From Hot Gaseous Halos, and Connections to Cosmological Accretion and Galactic Feedback Michael Anderson, MPA, Munich
Cosmological simulations predict that massive galaxies should be surrounded by very extended gaseous halos formed through a combination of accretion shocks and galactic feedback. These hot halos are ubiquitous in galaxy clusters and around elliptical galaxies, but galaxy groups are more diverse, and around spiral galaxies hot halos are only rarely detected. In this talk I describe two recent studies of the properties of these hot gaseous halos. In the former, we stacked data from 250,000 galaxies in the ROSAT All Sky Survey in order to measure average X-ray luminosity as a function of stellar mass across a range from small galaxies to medium-sized galaxy clusters. This uniform comparison shows that the LX - M* relation and the LX-M500 relation are both unbroken power-laws extending nearly all the way down to the mass of the Milky Way. We discuss the slope, normalization, and scatter of these relations, and show that these measurements are very informative about the nature of AGN feedback. In the latter study, we examine a single galaxy in detail - the giant spiral galaxy NGC 1961, which is one of the handful of spiral galaxies with a secure detection of a hot gaseous halo. Using deep XMM-Newton observations, we measure for the first time the temperature, metallicity, and deprojected density profiles of this hot halo. The low metallicity suggests that the halo is largely formed from material accreted from the IGM, although the influence of feedback on the profile is also evident. Finally, we compare the hot halo around this spiral galaxy to the hot halos seen around elliptical galaxies, concluding that it seems the total mass better determines the properties of the hot halo than the stellar mass of the central galaxy.
November 25, 2015 | 12:00 PM | ERC 401 | Special seminar Cosmological constraints from weak lensing: present measurements and future challenges Fabian Kohlinger, Leiden Observatory
Weak lensing is a powerful tool for cosmological inference. In this talk I will discuss two major applications, cosmic shear and galaxy-galaxy lensing, in the context of recent studies carried out together with my collaborators. In the first part I will discuss a technique to directly extract the matter power spectrum in different redshift bins from weak lensing measurements. I will show results from an application to state-of-the-art CFHTLenS data and discuss the constraints on cosmological parameters and neutrino mass. In the second part of my talk I will focus on the potentials and challenges of future large weak lensing surveys such as Euclid for cosmological constraints derived from galaxy cluster counts. For that accurate and precise cluster masses are paramount. In this context, I will discuss the impact of various sources of bias on weak lensing cluster mass estimates.
September 29, 2015 | 3:00 PM | ERC 401 | Open Group seminar Looking for primordial non-Gaussianity in Large Scale Structure: a new insight from the peaks approach to halo clustering Matteo Biagetti, University of Geneva
October 15, 2015 | 11:00 AM | ERC 401 | Open Group seminar Uniqueness of Massive Gravity Andrew Matas, Case Western Reserve University
Is the graviton a truly massless spin-2 particle, or can the graviton have a small mass? If the mass of the graviton is of order the Hubble scale today, it can potentially help to explain the observed cosmic acceleration. Previous attempts to study massive gravity have been spoiled by the fact that a generic potential for the graviton leads to an instability called the Boulware-Deser ghost. Recently, a special potential has been constructed which avoids this problem while maintaining Lorentz invariance. In this talk I will argue that the requirement of avoiding the Boulware-Deser ghost (or other degrees of freedom) is so powerful that the kinetic term and matter couplings for a massive graviton are fixed as well. In fact they must be exactly the same as in General Relativity. These results are remarkable: we derive the structure of General Relativity on the basis of stability requirements, not on a symmetry principle. I discuss implications of these results for cosmology and for other applications of massive gravity.
November 9, 2015 | 12:00 PM | ERC 401 | Open Group seminar Spectral analyses of gamma-ray millisecond pulsars and search for gamma-ray emission from super-luminous supernovae Nicolas Renault-Tinacci, Institut d'Astrophysique de Paris
Since its launch in August 2008, the Fermi γ-ray space telescope has opened a new window in the physics of pulsar, one of the most powerful accelerators in the universe. The Large Area Telescope has allowed the discovery of an important and still rapidly increasing number of γ-ray pulsars. In particular, nearly one half of the detected pulsed gamma-ray emitters is composed by old spun-up neutron stars, the millisecond pulsars (MSPs). Spectral analyses of the total and phase-resolved pulsed emission are essential to bring constraints to the theoretical models describing the electro-magnetic processes and regions of particle acceleration and high-energy radiations in pulsar magnetosphere. The gamma-ray data collected during five years of Fermi Large Area Telescope (LAT) observations have allowed in-depth spectral analyses of the total and phase-resolved emission from 25 of the brightest MSPs in the 50 MeV to 170 GeV energy band. The sample exhibits a significant evolutionary sequence in spectral energy distribution of the total pulsed emission. The sequence relates three spectral parameters, namely the spectral index at low energy, the apex energy at which the maximum energy flux is emitted, and the cut-off energy, with the spin-down power of the neutron star. As the latter increases, the spectral energy distribution broadens, softens, and shifts in energy. Spectral parameters change with phase present systematic patterns. Pulsars with aligned gamma-ray and radio peaks tend to be particularly luminous and soft. The sequence highlights an important transition in MSP evolution near a spin-down power of 10E27 W and the possible onset of a soft emission component in addition to curvature radiation. The phase dependence of the radiative efficiency also suggests that multiple emitting regions, with different levels of electric field screening, contribute to the total pulsed gamma-ray emission. Moreover, some very young pulsars, with specific characteristics, are supposed to be able to produced ultra-high-energy cosmic rays (UHECRs, E>10E18 eV). These very same objects could also be at the origin of the recent class of super-luminous supernovae (SLSNe). According to theoretical models SLSNe should be detectable from hard X-rays gamma rays. The Fermi-LAT, with 7 years of data and improve statistics thanks to a new reconstruction strategy, allows us to attempt at the detection of SLSNe or eventually to set gamma-ray flux upper limits. These measurements should help us understand this new growing class of supernovae as well as UHECR production by constraining models.
October 13, 2015 | 12:00 PM | ERC 576 | Tuesday Seminar Extreme Outflows and the FGas Around Galaxies Aleks Diamond-Stanic, University of Wisconsin-Madison
Our understanding of galaxy evolution centers around questions of how gas gets into galaxies, how it participates in star formation and black hole growth, and how it is returned to its galactic surroundings via feedback. On a global scale, measurements of the baryon density and the stellar mass function indicate that only 5% of baryons have formed stars by the present day, and this suggests that feedback from massive stars and supermassive black holes must prevent gas from forming stars in both low-mass and high-mass dark matter halos. I will present observational results on the geometry and kinematics of outflowing and inflowing gas around galaxies, including measurements of ejective feedback that is capable of quenching star formation by removing the cold gas supply. These results have broader implications for how gas is consumed and expelled at the centers of massive galaxies and for the limits of feedback from stellar radiation and supernovae. I will also discuss prospects for characterizing the physical properties of gas in and around galaxies using multi-wavelength spectroscopy with existing and future facilities.
November 10, 2015 | 12:00 PM | ERC 576 | Tuesday Seminar Catching Quenching Galaxies: Following the Road Less Traveled to Galaxy Transformation Katherine Alatalo, Carnegie Observatories
Modern day galaxies are found to be in a bimodal distribution, both in terms of their morphologies, and in terms of their colors, and these properties are inter-related. In color space, there is a genuine dearth of intermediate colored galaxies, which has been taken to mean that the transition a galaxy undergoes to transform must be rapid. I will discuss two such pathways galaxies take to rapidly transform from vibrant, blue spirals into quiescent, red elliptical and lenticulars, in particular, through the lens of the molecular gas. This includes the ways in which (1) AGN feedback (one of the proposed transformation mechanisms) and (2) constant harassment within compact groups can impact an environment that is rich in molecular gas, rendering it unable to form stars. I discuss new observations that have shown this phenomenon (as well as potential recipes to identify more of these objects), as well as the implications that these mechanisms have for galaxy evolution.
December 15, 2015 | 12:00 PM | ERC 161 | Tuesday Seminar 21cm Cosmology: The End of the Beginning Aaron Parsons, University of California, Berkeley
Since it was first proposed nearly two decades ago, measuring 21cm emission from neutral hydrogen in our early universe has tantalized us as a powerful probe of both cosmology and astrophysics. While the science case for 21cm cosmology, particularly during the Epoch of Reionization, is well established, the technical path toward measuring this signal has been more problematic. PAPER has recently distanced itself from its competitors, applying major technical breakthroughs to set the first physically meaningful upper limits on 21cm emission during reionization, and improving those limits a year later to show the presence of significant early heating. Even as PAPER's final season is under analysis, we are re-tooling our array to become HERA. New 14-m dishes are replacing PAPER's smaller elements, giving HERA the sensitivity to drive beyond the detection phase of 21cm cosmology, into the exciting era of data-driven modeling. The results will revolutionize our understanding of galaxy and star formation and even improve upon CMB cosmology.