Wine and Cheese Spring 2015: Difference between revisions
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Revision as of 03:06, 30 January 2015
This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2015.
Back to W&C Schedule
26 Jan 2015
Ingyin Zaw
Probing the Central Parsec of Active Galactic Nuclei with Water Masers
Determining the geometry and dynamics of the inner-most parsec of active galactic nuclei (AGN) is critical for understanding accretion and the relationship between the AGN and host galaxy. Water maser emission at 22 GHz provides a unique tracer, resolvable in position and velocity, of warm, dense molecular gas ~0.1-1.0 pc from the central engine. Furthermore, water masers exist in the narrow temperature range of ~400-1000K and can be used to probe the temperature and temperature gradient inside the AGN disk. I will discuss i) a test of disk heating in accretion models, using maser spectra and VLBI maps, ii) a study of the flow of material in NGC 4945, combining maser VLBI maps and multi-wavelength data, and iii) a search for new maser systems in the Southern Hemisphere, the Tidbinbilla AGN Maser Survey (TAMS).
Naoki Bessho
Particle acceleration during magnetic reconnection in ultrarelativistic electron-positron plasmas
In pulsar winds and jets from AGNs, plasma is considered to be composed of ultrarelativistic electrons and positrons with their Lorentz factors 10^3 to 10^6. How these high energy particles are produced is an open question, and magnetic reconnection is one of mechanisms to accelerate particles. We study magnetic reconnection in ultrarelativistic electron-positron plasmas by means of 2-D simulations that include kinetics of particle motion, and investigate particle acceleration mechanisms and energy spectra of accelerated particles.
02 Feb 2015
Marius Millea
Planck 2015 Constraints on the Cosmic Neutrino(-like) Background
The Planck 2015 results include the tightest measurements to-date of cosmic microwave background (CMB) temperature and polarization anisotropies up to few-arcminute angular scales. I will give a broad overview of the cosmology results from these data, with particular focus on what we have learned about the cosmic neutrino background (CNB). The new data allow more precise answers to questions such as 1) how much energy, parameterized by N_eff, is contained in the CNB? 2) what is the sum of the masses of the particles making up the CNB? and 3) are these particles really neutrinos, i.e. do they free-stream like neutrinos? One possibility I will explore is if some component of the CNB actually comes from axions or axion-like particles. Recent improvements in CMB and BBN data are shedding new light on this scenario. I will also discuss the status of agreement between Planck results and other cosmological probes such as BAO, H0, and low redshift structure measurements, and how the CNB may play a role in resolving tensions between some of them.
Colin Hill
Cosmology from the One-Point Function
Cosmological measurements have traditionally focused on the two-point correlation function or power spectrum. However, due to the non-gaussianity of the late-time density field, a vast amount of information potentially lies in the one-point probability distribution function (PDF) of various cosmological observables, such as the weak lensing (WL) convergence or thermal Sunyaev-Zel’dovich (tSZ) effect. We present analytic methods that allow for straightforward and efficient computations of these signals. Using data from the Atacama Cosmology Telescope (ACT), we explicitly demonstrate the power of the tSZ PDF, constraining the amplitude of density fluctuations with an error bar nearly twice as small as that obtained from ACT's earlier analysis of the tSZ skewness alone (with the same data). We extend these methods to the WL convergence field, for both CMB lensing and galaxy lensing, and verify their accuracy by comparing to ray-traced N-body simulations. Combining the WL PDF and power spectrum will increase the cosmological constraining power of upcoming surveys by at least a factor of two.
09 Feb 2015
Rongmon Bordoloi
TBD
TBD
23 Feb 2015
Rubab Khan
Massive Star Geriatrics
The evolution of the most massive stars such as Eta Carinae is controlled by the effects of mass-loss. Understanding these stars is challenging because no true analogs of Eta Car have been clearly identified in the Milky Way or other galaxies. Copious mass-loss leads to circumstellar dust formation, obscuring the star in the optical. But as the light is re-emitted by the dust, these objects become very luminous in the mid-IR. We have carried out a systematic search for Eta Car analogs in 7 galaxies, utilizing data from Spitzer, Herschel, HST and other sources. Our search detected no true analogs of Eta Car, however, we do identify a significant population of 18 lower luminosity (log(L/L_sun)=~5.5-6.0) dusty stars. This is consistent with all 25 < M < 60 M_sun stars undergoing an obscured phase at most lasting a few thousand years once or twice. The mass of the obscuring material is of order ~M_sun, and we simply do not find enough heavily obscured stars for these phases to represent more than a modest fraction (~10% not ~50%) of the total mass lost by these stars. While this search has been feasible using archival Spitzer data, JWST will be a far more powerful probe of these stars. The HST-like resolution of JWST will greatly reduce the problem of confusion and expand the possible survey volume.
Katy Daniel
TBD
TBD
09 Mar 2015
Nicole Czakon
Scaling Sunyaev-Zel'dovich Observables to Dark Matter Halos for Cluster Cosmology
The Sunyaev-Zel’dovich effect (SZE) is a powerful tool to study galaxy clusters out to large radii and to detect clusters at high redshifts. To first order, clusters are self-similar and one can link the SZE signal to a cluster’s physical properties by assuming a spherical distribution of matter in hydrostatic equilibrium. The SZE signal, however, will be affected by any astrophysical process that contributes non-thermal pressure support or if the cluster has non-spherical morphology. We have measured the SZE signal of 45 massive clusters using Bolocam at 140 GHz. After measuring the scaling relations of the SZE signal with total cluster mass, we find our clusters to be approximately 5-sigma shallower than the self-similar HSE prediction--a result that is in tension with most other SZE scaling relations studies. To confirm our measurements, we have implemented a series of tests to see whether, among others, sample selection, redshift, degree of disturbance, or alternative mass proxies might affect our measurements. We believe our results to be robust to the extent to which we are able to constrain the cluster properties with current observations. If confirmed, this would have a major impact on our understanding of galaxy clusters and cluster cosmology.
23 Mar 2015
Kendrick Smith
TBD
TBD
04 May 2015
Agnieszka Cieplak
TBD
TBD
