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.

Ely Kovetz (JHU)

Did EDGES Detect Dark Matter? The EDGES papers have presented some results that are difficult to understand. Ely Kovetz, who has worked on these particular issues, will walk us through the current understanding of these recent results.

March 19th

Ely Kovetz

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

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April 2nd

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April 9th

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April 16th

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April 23rd (Graduate Student Series)

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