Wine and Cheese Spring 2015

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2015.

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

Katherine Lee

CARMA Large Area Star Formation Survey (CLASSy)
I will present recent results from the CARMA Large Area Star Formation Survey (CLASSy) with a focus on the structures and kinematics of dense gas in Serpens Main. The survey mapped 150 square arcminutes of Serpens Main with an angular resolution of 7 arcsecs using N2H+(1-0), HCO+(1-0), and HCN(1-0) as dense has tracers. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. I will talk about the properties of the filaments, and their implications to the formation of the SE subcluster. Also, I will compare the properties of the filaments with the distribution of YSOs. The comparison suggests that the YSOs are formed on gravitationally unstable filaments. Finally, I will show velocity gradients perpendicular to the filaments at 0.03 pc scale across CLASSy regions. Such velocity gradients can be a natural consequence of converging flows.

Rongmon Bordoloi

Investigating the Milky Way’s Nuclear Outflow Kinematics
Recent observations with gamma ray emission to microwaves and polarized radio waves have detected giant lobes of plasma (Fermi Bubbles) extending above and below the Galactic plane of the Milky Way. These are possible signs of a Nuclear wind powered by either the central black hole or high-surface-density star formation, but our understanding is hampered by a lack of kinematic information. I will report the first results of a HST/COS survey to constrain the velocity of the outflowing gas within these regions, using ultraviolet absorption-line spectra.We perform a comprehensive spectroscopic program to survey the nuclear outflow in both the northern and southern Galactic hemispheres.We combine high-resolution STIS E140M observations of distant halo stars at low latitude with medium-resolution COS observations of AGNs at higher latitude. These sightline pass through a clear biconical structure seen in hard X-ray and gamma-ray emission of the Fermi Bubble. I will report detections of high velocity metal absorption lines, which cannot be explained by co-rotating gas in the Galactic disk or halo. Their velocities are suggestive of an origin on the front and back side of an expanding biconical outflow emanating from the Galactic center. We develop simple kinematic biconical outflow models that can explain the observed profiles with an outflow velocity of ~900/1000 km/s and a full opening angle of ≈110° (matching the X-ray bicone). This indicates Galactic center activity over the last ≈2.5-5.0 Myr, in line with age estimates of the Fermi Bubbles. The observations illustrate the use of UV spectroscopy to probe the properties of swept-up gas venting into the Fermi Bubbles.

16 Feb 2015

Yacine Ali-Haïmoud

Perturbative interaction approach to cosmological structure formation

The statistical properties of cold dark matter (CDM) in the non-linear regime make for a technically challenging problem, and their study has been the bread-and-butter of several generations of cosmologists. Standard analytical methods improve upon linear perturbation theory on quasi-linear scales, but usually fail dramatically at non-linear scales. A new and promising method was recently introduced by researchers in the field, relying on an expansion in the gravitational interaction, and using mathematical tools inspired by those of quantum field theory. This method seemed to produce results in good agreement with numerical simulations, deep inside the non-linear regime. In this talk, after reviewing standard perturbation schemes, I will lay out a simpler formalism for the perturbative interaction approach, using implicit forms for particle trajectories. I will show that this approach fails at recovering the linear growth factor on large scales, and that the apparent agreement on non-linear scales results from unjustified approximations. The problem of finding an analytical description of non-linear scales therefore remains open.

Nao Suzuki

Future SNIa surveys and Blackbody Spectra

Hyper Suprime-Cam (HSC) is a new wide-field camera on Subaru Telescope in Hawaii. HSC has a 1.5-degree field-of-view (FOV) in diameter with 104 CCD chips and 5 broad-band filters (g,r,i,z,y). Started from March 2014, a five-year survey program has been running, and I will introduce the survey plan and current status with emphasis on Type Ia supernova (SNIa) survey. Also, I will introduce a potential mid-size IR satellite mission, WISH (http://wishmission.org/en/index.html). In SNIa cosmology, the reduction of the systematic error is an urgent task, and I will propose how to reduce the calibration error by using white dwarfs with nearly a perfect blackbody spectrum.

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.

Jon Bird

Clues to Galaxy Formation from the Milky Way's Cosmological Context

Very different data sets guide galaxy formation theory across cosmic history: from the global properties of >10^7 galaxies at high redshift (z>0.5) to the kinematics and chemistry of >10^6 stars here in the Milky Way. Traditional observational and computational limitations have dictated independent study of these two regimes. I will discuss how this picture is changing rapidly and how viewing the MW as important boundary condition on galaxy evolution puts unprecedented demands on galaxy formation theory. In particular, I will discuss a novel disk formation mechanism and its signature in current observations of the Milky Way and the resolved kinematics of high redshift galaxies. Modern, high-resolution, cosmological galaxy formation simulations reveal that disks can grow ``upside-down" in the sense that progressively younger stellar populations are born with increasingly smaller vertical velocity dispersion, tracing the kinematics of the collapsing gas disk from which they form. We find that the upside-down model matches the most stringent observational constraints here in the MW, including the steep stellar age-velocity relationship measured in the solar neighborhood. I will argue that traditional interpretations of the MW stellar AVR contradicts evidence from IFU observations of high-redshift disk galaxies and must be revised. Our findings suggest that the ``upside-down model is currently the only self-consistent formation mechanism able to match kinematic constraints from z~2 to z~0. I will conclude with preliminary, yet tantalizing, evidence connecting the star formation history of simulated galaxies with their detailed morphology.

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

06 April 2015

Tomohiro Nakama

TBD
TBD

20 April 2015

Liang Dai

TBD
TBD

Jennifer Sobeck

TBD
TBD

04 May 2015

Agnieszka Cieplak

TBD
TBD