Wine and Cheese Fall 2018

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2018.

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.

10 September

Zaven Arazoumian (GSFC)

A NICER View: Astrophysics and Exploration from the International Space Station
Neutron stars are extraordinary in nearly every way. They are the densest objects in the universe, their gravity is immense, and they are the most powerful magnets known. Some -- those we call "pulsars" -- sweep narrow beams of radiation through space as they spin, sometimes as fast as blender blades, appearing to flash with unrivaled regularity like cosmic timepieces. Launched in June 2017, NASA's dual-purpose Neutron star Interior Composition Explorer (NICER) mission aims to answer longstanding questions about the physics and astrophysics of neutron stars, with a telescope on the International Space Station designed to investigate their X-ray emissions and precisely time their pulsations. The mission's second purpose is a first-ever demonstration of autonomous spacecraft navigation using pulsars as beacons in a "Galactic Positioning System." This presentation provides an overview of the NICER mission, its SEXTANT navigation demonstration, and the insights that NICER is delivering about neutron stars, black holes, and the high-energy processes that they drive.

17 September

Kathryn Johnston (Columbia)

Physical Manifestations of Evolution, Regularity and Chaos In and Around Our Galaxy
Our Galaxy is thought to be dynamically young with a fairly smooth potential dominated by a nearly spherical dark matter halo that has evolved little in the last several billion years. These attributes broadly suggest that potential evolution and dynamical chaos should have negligible influences on the orbits of its constituent stars, as well as on the stellar structures they collectively support. This talk reviews some recent results which point to signatures of Galactic evolution and the chaotic nature of stellar orbits that can be (and have been) observed.

24 September (GSS)

Alexander de la Vega (JHU)

Resolved Star Formation Trends in Massive Galaxies at z~1
Critical to our understanding of galaxy evolution is how galaxies stop forming stars and evolve from blue, star-forming disks to red, centrally concentrated spheroids. The processes that suppress star formation become important from redshift z ~ 1 to today, when red galaxies significantly increase in number density. Analyzing where stars form in different kinds of galaxies in this cosmic epoch can hint at the physics of star formation quenching. I present preliminary results of star formation radial profiles of ~1600 massive (>= 10^10 M_sun) galaxies in the CANDELS HST survey at 0.4 < z < 1.5. At z ~ 1, galaxies in transition between blue and red galaxies show central star formation rates consistent with the centers of blue galaxies. Star formation in the outskirts of these transition galaxies is lower by an order of magnitude and is more consistent with the outer parts of red galaxies. I juxtapose these trends with models of star formation quenching and discuss possible scenarios.

Hsiang-Chih Hwang (JHU)

Gas Accretion Caught in the Act
Gas accretion plays a crucial role in galaxy formation and evolution. Indeed, the growth in the stellar masses of galaxies over cosmic time occurs mainly through the accretion of gas from the environment, and no local star-forming galaxies can continue forming stars without replenishing their gas. As the inflow brings metal-poor gas into a galaxy, it lowers the metallicity in the local ISM, meaning that the metallicity distribution is a signpost to recent gas accretion. Therefore, we searched for regions with anomalously low metallicity in the IFU survey MaNGA. I will present how such regions are distributed within mergers, close pairs, and isolated galaxies, and how gas accretion happens in these systems. I will also discuss the lifetime of such regions, the balance between gas accretion and star formation rates, and the implication for galaxy evolution.

Weichan Wang (JHU)

Galaxy Inclinations and the Dust Attenuation Law at z~1.5
Measuring how fast galaxies form stars is the key step to understand galaxy formation at high redshift. The measurement is usually based on galaxy UV luminosity. However, high-redshift galaxies can be substantially obscured by dust in the UV and a proper correction for dust is needed. The correction is quantified by the infrared-to-UV luminosity ratio, IRX=L(IR)/L(UV). And IRX is usually inferred from the slope of galaxy UV spectrum, beta. We present the discovery that the relation between IRX and beta varies systematically with galaxy inclination. This applies to massive and star-forming disk galaxies (above 10^10 solar mass) at z~1.5. Such inclination dependence is consistent with a two-component model of dust distribution inside galaxies. Dust and stars are spatially mixed in the diffuse interstellar medium, and young stars are additionally surrounded by dust cocoons near their H II regions. Interestingly, for less massive galaxies at this epoch, we do not find evidence for a similar inclination dependence. This is likely because low-mass galaxies are more prolate and have disturbed gas kinematics.

1 October

Andrew Youdin (Steward Obs., U Arizona)

Binary KBOs, an Insight to Planetesimal Formation
Solar System planetesimals in binary pairs (also triples!) offer valuable clues to the history of our Solar System and to planet formation in general. Binaries in the most undisturbed regions of the Kuiper Belt are extremely common, and must have formed very early in Solar system history. Different theories for the formation of these binary KBOs have been proposed. The capture hypothesis describes dynamical capture, assisted by the dynamical friction of small rocks and ices. The collapse hypothesis appeals to fission during the gravitational collapse of small (~centimeter-sized) rocks and ices into ~10-100 km scale planetesimals. Aerodynamic concentration of solids by the streaming instability is a possible mechanism to trigger gravitational collapse, which can influence the properties of resulting binaries. I will argue that Solar System observations and theoretical considerations likely favor the collapse hypothesis, but that further observations and more refinement of theories are needed. The New Horizons flyby of 2014 MU69, apparently a close or contact binary, will provide the first up close look at this class of KBO.

Yuan-Sen Ting (IAS)

A New Era of Galactic Archaeology
Understanding physical processes responsible for the formation and evolution of galaxies like the Milky Way is a fundamental problem in astronomy. However, a key challenge is that the properties and orbits of the stars can only be observed at present: to understand what happened in the Milky Way at earlier epochs, one must explore “archaeological” techniques. The Galactic archaeology landscape is rapidly changing thanks to the various on-going large-scale surveys (Gaia, spectroscopy, asteroseismology) which provide a few orders of magnitudes more stars than before. In this talk, I will discuss the new "phenomenological" opportunities with these surveys. In particular, I will present a quantitative constraint on the radial migration of stars, the ISM enrichment history, the vertical heating of the Milky Way. I will also introduce a new set of tools for efficient measuring ab initio elemental abundances from both high and low-resolution R=2000 spectra (The Payne), for discovering spectroscopically unresolved binaries, and for inferring stellar ages and asteroseismic oscillation frequencies from low-resolution spectra.

8 October

Sara Ellison (UVic)

Galaxy mergers in the nearby universe
Galaxy mergers are predicted to play a critical role in shaping galaxies, by dramatically altering not only their morphologies, but also their star formation, nuclear accretion and internal chemistry. In this talk, I will give an overview our efforts to observationally test these predictions, including new results that test the prediction that star formation is quenched in late stage mergers due to the expulsion/consumption of the gas reservoir. Finally, I will show the first results from a study of spatially resolved merger properties using data from the MaNGA integral field unit survey.

Seunghwan Lim (UMass)

Gas Contents in the Low-z Universe
We used both the thermal and kinetic Sunyaev-Zel'dovich effect (tSZE and kSZE, respectively) to estimate the SZE flux from gas in halos, as well as to estimate the thermal energy of IGM gas in regions of different total matter density. As observational data, we used the Planck CMB temperature map, all-sky group catalog of Lim et al. 2017b, and a reconstruction of the large-scale structure such as the density field, tidal field, and velocity field based on the group catalog. As for the method, we employed the matched filter (MF) technique to maximize the detection. In particular, we did the MF simultaneously for all groups to take into account projections of nearby halos, which is predicted to be significant. Indeed, we show, using SZE lightcone maps constructed from simulations, that only the simultaneous MF can successfully recover the true SZE flux from the simulations, while the traditional MF and aperture photometry over-estimate the flux. Comparing simulations of different feedback models including EAGLE, Illustris, and IllustrisTNG, we also show that our results about IGM gas can constrain galaxy models.

15 October

Darryl Seligman (Yale)

`Oumuamua!
I will review what is certain, what is speculative, and what is still completely mysterious about the first interstellar object observed to traverse the Solar System. The talk will delve into `Oumuamua's origin, its unusual dynamics, and its physical properties. I will discuss the prospects for detecting additional such objects with LSST, as well as the prospects for in situ exploration of future interstellar visitors that are detected with sufficient advance warning.

Alice Pisani (Princeton)

Precision Cosmology with Cosmic Voids
Modern surveys allow us to access to high quality measurements on large areas in the sky and at high redshift — thus sampling the galaxy distribution in detail also in the emptier regions, voids. Void cosmology is hence becoming an increasingly active sector of galaxy clustering analysis: by measuring void properties, such as the abundance or the density profiles, it is possible to constrain cosmological parameters. The void perspective is particularly promising to better understand dark energy: voids being by definition devoid of matter, their dominant component is dark energy and the effects of this component are expected to be more evident on voids. However another possibility to justify current observations is to consider a modification of the laws of General Relativity. Cosmic voids constitute a sweet spot where the effects of modifications of General Relativity would be more prominent. In this talk I briefly illustrate the use of cosmic voids as a tool for cosmology, I present recent developments on the field and discuss on the constraining power of voids that will be observed by upcoming surveys such as WFIRST and Euclid.

22 October (GSS)

Joseph Cleary (JHU)

Variable-delay Polarization Modulators on the Cosmology Large Angular Scale Surveyor
The Cosmology Large Angular Scale Surveyor (CLASS) is measuring the polarization of the Cosmic Microwave Background (CMB). These observations will better constrain the physics of reionization and potentially find evidence of inflation. To do so, the CLASS instrument must make extremely sensitive and stable observations. The key technology to achieve the required stability will be a front-end polarization modulator that will encode the polarization signal at frequencies above those of many noise sources. The observational stability of CLASS sets it apart from other CMB experiments.

Bingjie Wang (JHU)

Modeling the 21-cm Signal
Observations of the early Universe with the 21-cm line of neutral hydrogen promise to complete our knowledge of cosmic structure formation from the dark ages to the epoch of reionization. The recent EDGES detection of an absorption profile around redshift 17, with a best-fit amplitude more than twice the limit imposed by the standard cosmological model, has excited renewed interests in modeling the 21-cm signal. In this talk I will present our effort in developing a tool which aims to explore a wide range of parameter space of the 21-cm signal, both within the standard cosmology and beyond. In particular, I will discuss the dark matter explanation of the EDGES detection.

Speaker

Title
Abstract

29 October

Kevin France (Colorado)

Ultraviolet Spectroscopy from Suborbital and SmallSat Platforms: Little NASA Missions Supporting Big NASA Observatories and Bigger Science
Ultraviolet spectroscopy is a powerful tool for quantifying the physical state of molecular, neutral, and ionized gas in the universe. From the circumgalactic gas reservoirs around distant galaxies to the circumstellar disks out of which planets are born, ultraviolet (90 – 320nm) emission and absorption lines provide unique diagnostics of the composition, temperature, kinematics, and excitation conditions of these regions. As we look to the science capabilities of future large missions (e.g., the Large/Ultraviolet/Optical/InfraRed (LUVOIR) Surveyor), we require UV instruments that are both more efficient and more capable than our flagship instruments of today (HST/STIS and COS). Future UV spectrographs will rely on advanced components: UV mirror coatings, diffraction gratings, large format photon-counting detectors, and multi-object field selectors. These components are currently being developed and flight-tested through NASA’s suborbital research program.

In this talk, I will present an overview of NASA’s sounding rocket + cubesat science and technology program. I will focus on the development of hardware required to realize the LUVOIR Ultraviolet Multi-Object Spectrograph (LUMOS), an ambitious UV spectroscopy and imaging instrument for LUVOIR. I will discuss two University of Colorado sounding rocket payloads (CHESS and SISTINE) that are demonstrating detector, coating, grating, and optical designs currently baselined for LUVOIR. I will also describe two cubesat missions in development (CUTE and SPRITE), highlighting the power of small UV spectrographs to provide unique data on topics as diverse as atmospheric escape from exoplanets to ionizing radiation escape from star-forming galaxies.

5 November

Paz Beniamini

Observational constraints on the structure of gamma-ray burst jets and lessons from GW170817
Motivated by GW170817 we examine three independent constraints on the angular structure of gamma-ray burst (GRB) jets that are required by observations of cosmological long GRBs. We find that efficient gamma-ray emission has to be restricted to material with Gamma>50 and is most likely confined to a narrow region around the core. Comparing GRB170817 with the regular population of short GRBs (sGRBs), we show that an order unity fraction of NS mergers result in sGRB jets that breakout of the surrounding ejecta, that their luminosity function must be intrinsically peaked and that sGRB jets are typically narrow with opening angles ~ 0.1 rad. Finally, we perform Monte Carlo simulations to examine models for the structure and efficiency of the prompt emission in off-axis sGRBs. We find that only a small fraction, 0.01-0.1, of NS mergers detectable by LIGO/VIRGO in GWs is expected to be also detected in prompt gamma-rays, and GW170817-like events are very rare.

Melanie Habouzit

Black Hole Formation and Feedback
Over the last decade, we have come to appreciate that supermassive black hole of millions of solar masses and above are commonly hosted by massive galaxies, but are also present in local dwarf galaxies. Black holes are a fundamental component of galaxies, but their origin and their ability to impact their host galaxies are still far from being understood. I will present recent results of the new IllustrisTNG simulations, particularly the time evolution of the BH and galaxy populations. There has been much debate in the literature to understand the physical mechanisms responsible for quenching massive galaxies, i.e., suppressing star formation in time. I will discuss how this is done in IllustrisTNG, and to what extent it agrees with observational constraints.

12 November

Richard Miller (APL)

Ex Luna Scientia! The Lunar Occultation Explorer (LOX) and Transformational Astrophysics Enabled by the Moon
Astronomical investigations from the Moon afford new opportunities to advance our understanding of the cosmos. The Lunar Occultation Explorer (LOX) will leverage the power of a new observational paradigm to transform our understanding of the nuclear cosmos (0.1–10 MeV) and establish the Moon as a platform for astrophysics. LOX directly challenges traditional paradigms to circumvent the mission complexity, technology development lifecycles, and cost constraints that have limited the tremendous potential of nuclear gamma-ray (MeV) astrophysics to date. Temporal modulation is the foundation of our approach. Operating from lunar orbit, LOX will use the Moon as a natural occulting disk to generate the required modulation via repeated eclipses of astronomical sources. The resulting occultation signatures contain all the information necessary for source characterization and localization. Simplicity is a hallmark of this efficient and validated approach. LOX’s lone instrument, the Big Array for Gamma-ray Energy Logging (BAGEL) is highly scalable, limited only by available mission mass and power resources. Nuclear astrophysics is ripe for new discoveries and cracking open this critical window will reveal the details of essential astrophysical phenomena in one of the least explored cosmic domains. I will review ongoing development of the LOX mission including in-situ validation of the technique from lunar orbit, discuss the benefits of the lunar environment, and highlight several high-priority science goals uniquely enabled by LOX that will provide new insights into the lifecycle of matter and energy in our galaxy and beyond.

19 November

Chi-Ho (Edwin) Chan (Racah Institute)

Magnetorotational Instability in Eccentric Disks
Eccentric disks arise in such astrophysical contexts as tidal disruption events, but it is unknown whether the magnetorotational instability (MRI), which powers accretion in circular disks, operates in eccentric disks as well. We examine the linear evolution of unstratified, incompressible MRI in an eccentric disk orbiting a point mass and threaded with a vertical background magnetic field. Much like in circular disks, MRI grows when the field is weak, but the growth per orbit declines slightly with increasing eccentricity; unlike in circular disks, MRI grows in highly eccentric disks even when the field is extremely strong. Eccentric MRI can be understood either as the competition between orbital shear and magnetic tension; or as the parametric destabilization of magnetic modes by eccentric orbital motion, which is resonant at small eccentricities.

26 November (GSS)

Hiro Nishikawa (JHU)

Core Formation and Collapse of Self-Interacting Dark Matter Halos and Subhalos
Self-interacting dark matter (SIDM) has remained a viable candidate of dark matter, as it may overcome some of the challenges the standard collisionless cold dark matter paradigm faces in small-scale structures, such as the core-cusp problem. In this talk, I will explore the evolution of dark matter halos and subhalos in the presence of SIDMs through the use of gravothermal fluid approximation. In particular, I will talk about the evolution of SIDM subhalos that undergo tidal disruption and show that it subsequently leads to formation of denser cores or core collapses, which may provide a new mechanism in creating intermediate mass black holes at the centers of such halos.

Kaze Wong (JHU)

The Potential of Multiband Gravitational Wave Astronomy
Some recent developments in multiband data analysis have prompted us to explore the prospects of multiband gravitational wave science. A ground-based detector network has detected several stellar-mass black hole merger events, and many more detections are expected in the near future. A space-based detector such as LISA could observe the early inspiral of these systems. Multiband observations can improve our ability to determine source parameters by removing degeneracies, and possibly allow us to measure parameters (such as the orbital eccentricity) that may not be measurable on the ground. Space-based inspiral detections could allow us to forecast merger events observable from the ground; vice versa, by post-processing LISA data and exploiting coincidence with mergers observed on the ground we could be able to detect LISA inspirals that would otherwise be sub-threshold. We will quantify these possibilities and discuss some of their astrophysical implications.

3 December

Thomas Essinger-Hileman (GSFC)

Results from the Atacama B-Mode Search (ABS)
The Atacama B-mode Search is an experiment designed to measure the cosmic microwave background polarization. It observed at 145 GHz from a site at 5,190 m elevation in northern Chile. The noise equivalent polarization temperature, or NEQ, is 41 uK*rt(s). One of the unique features of ABS is its use of a rapidly rotating ambient-temperature half-wave plate (HWP) as the first optical element. The HWP spun at 2.55 Hz to modulate the incident polarized signal at frequencies above where instrument white noise dominates over atmospheric fluctuations and other sources of low-frequency noise. I will present the analysis of data from a 2,400 sq. deg. region of sky. We perform a blind analysis to reduce potential bias. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky, with a derived calibration factor of 0.89 +/- 0.10. We marginally detect polarized dust emission (at 3.2-sigma for EE and 2.2-sigma for BB) and give an upper limit on the tensor-to-scalar ratio of r < 2.3 (95% confidence level) with the equivalent of 100 on-sky days of observation. We also present a new measurement of the polarization of Tau A and introduce new methods for calibration and data analysis associated with HWP-based observations.

Claire Murray (JHU)

Taking the Temperature of the Local Interstellar Medium
A precise observational accounting for physical conditions of gas and dust in the Galactic interstellar medium (ISM) is vital both for correcting observations of extragalactic light and for resolving the bottleneck between mass reservoirs and star formation in galaxies. A key phase in the ISM lifecycle is occupied by neutral hydrogen (HI), whose temperature and density are crucial for understanding the formation of star-forming cloud complexes from the ambient neutral medium. However, multiphase HI properties remain mysterious due to limited direct measurements of HI optical depth and uncertainty in how and whether this material can be traced by dust. I will present results from the deepest-ever study of HI properties via 21cm absorption at the Karl G. Jansky Very Large Array, 21-SPONGE. We detect an unexpectedly ``warm" neutral medium and a significant fraction of thermally unstable gas, emphasizing the importance of dynamical processes for regulating the ISM and the need for new 21cm excitation models. Furthermore, although cold HI is ubiquitously detected in absorption, its optical depth is not sufficient to entirely account for ``dark gas". I will finally discuss applications of machine vision for characterizing 21cm spectra and making objective comparisons with numerical simulations, as well as future Galactic surveys with SKA pathfinder telescopes.