Wine and Cheese Spring 2018

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2017.

Wine and Cheese sessions with one talk will have a 50 minute talk with 10 minutes for questions. Sessions with two speakers will have two 25 minute talks, each with 5 minutes for questions. Sessions in the Graduate Student Series will have three 15 minute talks, each with 5 minutes for questions.

February 5th (Graduate Student Series)

Katie Harrington

Variable-delay Polarization Modulators for the CLASS Telescopes
The search for inflationary primordial gravitational waves and the optical depth to reionization, both through their imprint on the large angular scale correlations in the polarization of the cosmic microwave background (CMB), has created the need for high sensitivity measurements of polarization across large fractions of the sky at millimeter wavelengths. These measurements are subjected to instrumental and atmospheric 1/f noise, which has motivated the development of polarization modulators to facilitate the rejection of these large systematic effects.

Variable-delay polarization modulators (VPMs) are used in the Cosmology Large Angular Scale Surveyor (CLASS) telescopes as the first element in the optical chain to rapidly modulate the incoming polarization. VPMs consist of a linearly polarizing wire grid in front of a moveable flat mirror; varying the distance between the grid and the mirror produces a changing phase shift between polarization states parallel and perpendicular to the grid which modulates Stokes U (linear polarization at 45°) and Stokes V (circular polarization). The reflective and scalable nature of the VPM enables its placement as the first optical element in a reflecting telescope. This simultaneously allows a lock-in style polarization measurement and the separation of sky polarization from any instrumental polarization farther along in the optical chain.

Erini Lambrides

Running Up The Gas Bill, The Cost of Leaving Your AGN On: Warm Molecular Gas and Dust in Active Galaxies
We analyze 2015 mid-infrared spectra of active and star-forming galaxies to determine if and how accreting, super-massive black holes at the center of galaxies impact the interstellar medium of their hosts. We assess the AGN's impact on the gas and dust of their host galaxies by compiling the largest sample of extragalactic objects with mid-infrared spectroscopic data, and performing a suite of diagnostics and statistical tests. We provide a large census of rotational molecular hydrogen emission in the context mid-infrared star-formation and AGN activity diagnostics. We find a statistically significant positive correlation between excess molecular hydrogen emission and the relative contribution of the AGN to the IR emission. We find a 200K difference between the excitation temperatures of the higher pure rotational molecular hydrogen transitions in AGN dominated and non-AGN dominated spectra. We interpret our findings as evidence of distinct differences in the star-forming molecular gas in AGN host galaxies, and interpret our molecular hydrogen temperature differences as evidence of AGN host galaxies having a warmer or more dense warm molecular hydrogen component. Thus we find evidence of a distinctly different population of molecular hydrogen gas that exists in AGN host galaxies.

David Ely

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February 12th

Amiel Sternberg (Tel Aviv University, Israel; Max Planck Institute for Extraterrestrial Physics, Germany; Flatiron Institute)

The Atomic to Molecular (HI-to-H2) Transition in Galaxy Star-Forming Regions
The atomic to molecular hydrogen (HI-to-H2) phase transition is of fundamental importance for star-formation and the emergence of chemical complexity in the interstellar medium of galaxies. I will present an overview, and discuss recent theoretical studies, numerical and analytic, of the HI-to-H2 transition in irradiated systems, with applications to the multi-scale behavior observed in star-forming galaxy disks from low- to high-redshift.

February 19th

Margaret Meixner (STSci)

The Origins Space Telescope - a NASA Decadal Mission Study
The Origins Space Telescope is an evolving concept for the Far-Infrared Surveyor mission, and the subject of one of the four science and technology definition studies supported by NASA Headquarters to prepare for the 2020 Astronomy and Astrophysics Decadal Survey. The Origins Space Telescope will discover or characterize exoplanets, the most distant galaxies, nearby galaxies and the Milky Way, and the outer reaches of our solar system. This talk will present the science drivers and broad capabilities of the Origins Space Telescope Mission Concept 1. The telescope is a ~9 m off-axis, segmented telescope that is cryogenically cooled to ~4K. A baffle and cryocoolers ensure the telescope environment is maintained at ~4K. The primary is deployed and the secondary is fixed inside the instrument accommodation module. Five instruments covering 5 to 660 μm enable the broad range of scientific activity: Medium Resolution Scanning Spectrometer, R~500 and R~40,000 for 30-660 μm; Far-Infrared Imaging Polarimeter, 40, 80, 120 and 240 μm simultaneous imaging; High Resolution Spectrometer, R~105 and R~106 for 25-200 μm; Heterodyne Instrument, R~106-107 for 63 μm and 111 to 566 μm; and Mid-Infrared Imager, Spectrometer and Coronagraph, 5 to 38 μm, R~300, 1000 and 20,000 with special transit spectrometer channel. The telescope, instrument accommodation module, sunshield and spacecraft would be launched in an 8 m sized fairing. The scope of the Mission Concept 2, similar area as JWST, will also be discussed.

Ai-Lei Sun (JHU)

Discovering AGN extended emission line regions -- an automated search with Subaru Hyper-Suprime Cam Survey
The ionizing radiation from luminous AGN creates large narrow-line regions on galactic scales. The emission from these regions is useful for the studies of AGN ionization, obscuration, and feedback. In this talk, I will introduce a new and automated approach to search for and study these regions with broadband imaging surveys, which offers greater statistical power than traditional targeted observations. This approach is applied to SDSS obscured AGN samples and images from the Subaru Hyper-Suprime Cam Survey. I will highlight candidates of extended emission line regions and discuss what we can learn about AGN photoionization.

February 26th

James Stone (Princeton)

Super Eddington Black Hole Accretion Flows
Super Eddington accretion occurs in many systems, such as the inner regions of quasars and luminous AGN, ultra-luminous X-ray sources (ULXs), and tidal disruption events. Understanding such flows is important not only for interpreting the spectra and variability of these sources, but also to predict the rate of growth of black holes in the early universe, and to quantify energy and momentum feedback into the medium surrounding the black hole, a process likely to be important in controlling galaxy formation in the case of AGN. New results from a study of the magnetohydrodynamics of luminous accretion flows, in which radiation pressure dominates, will be presented. We have developed new numerical methods based on a formal solution of the time-dependent radiation transfer equations to study this regime. Our numerical simulations reveal new effects that require extension of standard thin-disk models. We discuss these results, and their implications for the astrophysics of accreting black holes.

March 5th

Jane Rigby (GSFC)

The Definitive UV Spectral Atlas of Star-Forming Galaxies at Cosmic Noon he rest-frame ultraviolet diagnostics that JWST will use to study galaxies at cosmic dawn sorely need to be tested and calibrated. We are measuring these diagnostics now with Project MEGaSaURA: The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA is an atlas of high signal-to-noise, medium spectral resolution (R~3000) spectra of 15 extremely bright gravitationally lensed galaxies at redshifts of 1.7<z<3.6. The sample, selected from the SDSS Giant Arcs Survey, comprises 15 of the brightest known lensed galaxies; the brightest have apparent magnitudes of g_AB=20–21, which means they appear 30 to 70 times brighter than the typical Lyman Break Galaxy. The MEGaSaURA spectra reveal a wealth of spectral diagnostics: absorption from the outflowing wind; faint nebular emission lines that will be key diagnostics for JWST, GMT, and TMT; and photospheric absorption lines and P Cygni profiles from the massive stars that power the outflow. The stacked MEGaSaURA spectrum reveals still weaker spectra diagnostics -- with considerably better wavelength coverage and spectral resolution than previous composites, the MEGaSaURA stack is the highest-quality spectrum yet obtained of star-forming galaxies at cosmic noon. We have released the spectra to the community.

March 12th

Anna Lisa Varri (Edinburgh)

Blurring the Star Cluster - Galaxy Divide
The nature of faint stellar systems at the interface between classical globular clusters and dwarf galaxies is currently at the centre of much attention, as they represent the lower limit to the dark matter clustering scale and their properties and demographics provide crucial insight into many open problems in galaxy formation. Dynamical investigations of such objects are usually polarised around a sharp dichotomy: if they are approached as star clusters, they are studied as collisional, dark matter-free objects; if they are treated as satellite galaxies, they are considered as collisionless and dark matter-dominated. But many stellar systems actually fall into the perplexing regime at the interface between collisional and collisionless dynamics, and their dark matter content is hard to pin down. Driven by these motivations, I will present the first results of a new investigation of the equilibrium and evolutionary properties of collisional stellar systems embedded in small, stationary, dark matter halos.

March 19th

Ely Kovetz (JHU)

Did EDGES Detect Dark Matter?
The EDGES (Experiment to Detect the Global Epoch of Reionization Signature) collaboration has recently reported a detection of an absorption profile of CMB photons in neutral hydrogen centered around 78MHz (corresponding roughly to redshift 17). While some aspects of the EDGES measurement are consistent with the general expectation from the cosmic dawn signal, others are in stark contradiction to the standard LCDM prediction. In particular, the amplitude of the absorption trough is several standard deviations below the largest possible absorption amplitude allowed, indicating that either the background radiation temperature was much higher than expected, or that the gas temperature at the cosmic dawn epoch was much lower than expected. The latter had been predicted as a possible signature of coulomb-type interactions between dark matter and baryons, and has now been suggested as a possible explanation for the EDGES result. We will describe the 21cm measurement as well as the possible indication for new physics, and place heavy emphasis on the serious caveats to both.

March 26th

Michael Busch (JHU)

Tracing Dark Molecular Gas with OH 18-cm Emission using the Green Bank Telescope
The formation of molecules out of hydrogen and other atoms in the interstellar medium (ISM) is one of the most important steps in star formation: that is, stars form exclusively in molecular clouds. The largest component of this gas, cold molecular hydrogen, is practically invisible due to the lack of a dipole moment and no easily excited rotational and vibrational states. Most astronomers attempt to trace molecular hydrogen using emission from other molecules, and specifically the CO molecule. In this talk I'll present the results of a highly sensitive, dense one-square-degree Green Bank Telescope survey of the ground-state 18cm OH lines which appear to trace molecular hydrogen in areas that are largely devoid of CO emission. I'll also present diffuse cloud models to explore the physical conditions of the gas in the survey area and present arguments for why the OH molecule can effectively trace the diffuse molecular gas where CO is unable to.

Tanvi Karwal (JHU)

Generalised Dark Matter
My talk will introduce the generalised dark matter model, a powerful phenomenological model that can emulate the effects of various dark matter and dark energy candidates. I will motivate the need for such a model, discuss its effects on the cosmic microwave background (CMB) and how it can help diminish the low multipole tension in the CMB temperature spectrum.

Daniel Pfeffer (JHU)

Probing The Effects of Interacting Dark Matter
In this talk I will discuss the impact of millicharged dark matter on the CMB. Various interactions between dark matter and standard model particles will modify the CMB in different ways and I will describe these effects. Previous works on interacting dark matter have mainly included individual interactions at a time, such as scattering with either photons or baryons. These different interactions dominate the constraints at different times in cosmic history. My work will include the effects of all these interactions and therefore lead to more realistic constraints.

April 2nd

Jennifer Wojno (JHU)

Correlations between age, kinematics, and chemistry as seen by the RAVE survey
We explore the connections between stellar age, chemistry, and kinematics across a Galactocentric distance of 7.5 < R(kpc) < 9.0, using a sample of ∼ 12000 intermediate-mass (FGK) turnoff stars observed with the RAdial Velocity Experiment (RAVE) survey. The kinematics of this sample are determined using radial velocity measurements from RAVE, and parallax and proper motion measurements from the Tycho-Gaia Astrometric Solution (TGAS). In addition, ages for RAVE stars are de- termined using a Bayesian method, taking TGAS parallaxes as a prior. We divide our sample into young (0 < τ < 3 Gyr) and old (8 < τ < 13 Gyr) populations, and then consider different metallicity bins for each of these age groups. We find signif- icant differences in kinematic trends of young and old, metal-poor and metal-rich, stellar populations. In particular, we find a strong metallicity dependence in the mean Galactocentric radial velocity as a function of radius (∂VR/∂R) for young stars, with metal-rich stars having a much steeper gradient than metal-poor stars. For ∂Vφ/∂R, young, metal-rich stars significantly lag the LSR with a slightly positive gradient, while metal-poor stars show a negative gradient above the LSR.

Wenlong Yuan (JHU)

Period-Luminosity Relations of Mira Variables and Their Application to the Extragalactic Distance Scale
The Mira Period-Luminosity relations (PLRs) at near- and mid-infrared wavelengths are promising distance indicators, with brighter absolute magnitudes than Cepheids, comparable PLR dispersion and ubiquitous presence in all galaxy types. We developed a semi-parametric Gaussian process periodogram method for sparsely-sampled Mira light curves and discovered more than 1800 Miras in M33 using machine-learning techniques. We derived tight near-infrared PLRs for the LMC Miras, which was used to derive a Mira-based distance to M33. I will present an overview of the Gaussian process model, the Random Forest classifiers, and the resulting PLRs.

April 9th

Chris Howk (Notre Dame)

The Positive Side of the Galactic Baryon Ledger: the Evidence for Cold Inflow
The flow of gas through galactic halos is crucial to the evolution of galaxies, as the nature of such flows can dictate the star formation properties of galaxies and regulate their metallicity. Outflows through the circumgalactic medium (CGM) carry metals away from galaxies (although many may return), while infalling metal-poor gas from the intergalactic medium dilutes the metals in galaxies and provides new fuel for star formation. The nature of the infalling baryons, in particular, is of great interest, but such gas has historically been difficult to identify. I'll review our work on galaxies both near and far that suggests the inflow of new matter is robust even in today's massive galaxies, both at the halo scale and the disk scale.

April 16th

Abigail Vieregg (Chicago)

Discovering the Highest Energy Neutrinos Using a Radio Phased Array
Ultra-high energy neutrino astronomy sits at the boundary between particle physics and astrophysics. The detection of the highest energy neutrinos would be an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. IceCube has detected astrophysical neutrinos at lower energies, and at higher energies the best limits to date on the flux comes from IceCube and the ANITA experiment, a NASA balloon-borne radio telescope designed to detect coherent radio Cherenkov emission from cosmogenic ultra-high energy neutrinos. The future of high energy neutrino detection lies with ground-based radio arrays like ARA, which would represent an large leap in sensitivity. I will discuss a new radio phased array design that will improve sensitivity enormously and could push the energy threshold for radio detection down to overlap with the energy range probed by IceCube.

April 23rd (Graduate Student Series)

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April 30th

Britton Smith (SDSC)

Where did the first normal stars come from?
It is well known that stars observed in the local Universe form with something very close to a universal initial mass function (IMF) where the vast majority are of low mass. However, theory and simulations of the formation of the first stars in the Universe predict a top-heavy IMF with significant dependence on environment. How and when does this transition occur? I will report on the Pop2Prime simulations, which begin with cosmological initial conditions and end with the collapse and fragmentation of metal-enriched gas on scales of a few hundred AU. With these simulations, we are able to study the physical conditions in which the oldest stars observed formed as well as the means by which star-forming gas was first enriched with metals.

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