DRAO Seminar Series 2022


Time & Date Speaker Title
14:00 Wed Jan 12 Natasha Maddox
Ludwig Maximilian University of Munich
Remote Talk: New results from the MIGHTEE survey: Neutral hydrogen over the past 1 billion years
14:00 Wed Feb 9 Samantha Lawler
University of Regina (Campion College)
Remote Talk: Megaconstellations of satellites are about to ruin the night sky for everyone
14:00 Wed Feb 23 Aris Tritsis
University of Western Ontario / CITA
Remote Talk: Halo’s Magnetic field as Evident from stRiated Interstellar Clouds (HOMERIC)
14:00 Wed Mar 9 Daniel Rybarczyk
University of Wisconsin-Madison
Remote Talk: Constraining the atomic conditions suitable for the formation of diffuse molecular gas
14:00 Wed Mar 23 Simon Foreman
Perimeter Institute, CHIME
Remote Talk: Detection of Cosmological 21cm Emission with CHIME
11:00 Wed Apr 6 Sareh Ataiee
Ferdowsi University of Mashhad
Remote Talk: Do discs allow the planets get close to their host stars?
14:00 Wed Apr 20 James Stone
Institute for Advanced Study
Remote Talk: Magnetohydrodynamic Turbulence in the ISM
14:00 Wed May 4 Deborah Good
University of Connecticut, CHIME
Remote Talk: Pulsar Timing Arrays CHIME in on Gravitational Waves
May 16-20 CASCA https://uwaterloo.ca/canadian-astronomical-society/
11:00 Wed Jun 15 Raphael Skalidis
University of Crete, Greece & Institute of Astrophysics
Remote Talk: Precision Galactic magnetometry through dust polarization

Remote Talk: New results from the MIGHTEE survey: Neutral hydrogen over the past 1 billion years

Natasha Maddox (Ludwig Maximilian University of Munich)

We present the newest results from the HI branch of the MeerKAT large survey project MIGHTEE. With only a fraction of the full survey area, the data are already revealing structures traced in HI that have gone undiscovered at other wavelengths, including galaxy groups with exceptionally high HI fractions, challenging models of group assembly. The sensitivity of the telescope enables scaling relations defined with targetted observations at z=0 to be extended over the previous billion years, including the Tully Fisher relation. The new parameter space probed by MIGHTEE is providing a view of galaxy evolution missing from observations with previous telescopes.

Remote Talk: Megaconstellations of satellites are about to ruin the night sky for everyone

Samantha Lawler (University of Regina / Campion College)

Several companies are starting to launch megaconstellations of thousands of communication satellites (satcons), which would increase the number of active satellites in Low Earth Orbit at least twenty-fold in the next few years. SpaceX’s Starlink satcon is currently largest (almost 2,000 satellites) and is adding 60 new satellites every couple of weeks. While these satcons do allow internet access in many underserved rural and remote locations, the costs are prohibitively high for all but the most well-off customers. These thousands of satellites each reflect sunlight, causing serious problems for research astronomy, and making anthropogenic light pollution a fully global phenomenon that cannot be escaped anywhere on Earth. Our recent simulations show that because of geometry and the chosen satellite orbits, latitudes near 50 degrees N and S will see the worst light pollution from these satcons, with hundreds of naked-eye visible satellites all night long in the summer. These satellites also contribute to significant atmospheric pollution, both on launch and re-entry, contribute to diffuse sky emission, and drastically increase the very real threat of Kessler Syndrome. I will talk about how these satellites will affect stargazers and astronomers worldwide, and what you can do to help mitigation efforts.

Remote Talk: Halo’s Magnetic field as Evident from stRiated Interstellar Clouds (HOMERIC)

Aris Tritsis (University of Western Ontario / CITA)

From the propagation of cosmic rays and the removal of CMB foregrounds to the formation of molecular clouds and star formation, the Galactic magnetic field (GMF) plays a paramount role. Despite the importance of the GMF, unveiling its properties has proven to be, like the journey of Ulysses to Ithaca in Homer’s epic poem, a real Odyssey. This is not because of lack of effort but rather because the magnetic field is hard to observe. The majority of the diagnostics we have been using to probe the GMF cannot provide 3-dimensional information about its strength or structure. In this talk, I will present HOMERIC (HalO’s Magnetic field as Evident from stRiated Interstellar Clouds), an ambitious project that aims to perform a bona-fide tomographic measurement of the strength and orientation of the plane-of-sky component of the GMF. To this end, HOMERIC makes use of a novel method that utilises the imprint of hydromagnetic waves on interstellar clouds to trace back the strength of the magnetic field. The importance of the magnetic field and non-ideal magnetohydrodynamic (MHD) effects in the context of star formation will also be discussed.

Remote Talk: Constraining the atomic conditions suitable for the formation of diffuse molecular gas

Daniel Rybarczyk (University of Wisconsin-Madison)

Neutral hydrogen (HI) is the main ingredient for molecule formation and survival in the diffuse ISM. Yet, the role and importance of multiphase HI structure in the transition from atomic to molecular gas is still not understood. We have used observations of HI emission and absorption (Arecibo, VLA) and observations of HCO+, CCH, HCN, and HNC absorption (ALMA, NOEMA) to connect the early stages of molecule formation in the diffuse ISM with the underlying atomic gas properties. We find that these molecular species form along sightlines where AV > 0.25, similar to the HI-to-H2 transition at solar metallicity, and where the cold neutral medium column density is >1020 cm-2. The sightlines with the highest molecular column densities also have the most thermally unstable HI, suggesting that the unstable HI plays an important role in molecule formation and survival. We also detect a broad, faint component to the HCO+ absorption that spans most velocities where HI absorption is observed. This faint component is coincident in velocity with HI that has a low cold neutral medium fraction. We also find thresholds for the optical depth, temperature, and turbulent Mach number of HI gas structures with a molecular component. By comparing to PDR chemical model predictions, we find that the kinetic temperature and the thermally unstable HI fraction separate our sample into two distinct categories. A lower HCO+ column density sample can be explained with modest density, FUV radiation field, and cosmic ray ionization rate (CRIR) models, while a higher HCO+ column density sample requires models with high density, FUV radiation field, and CRIR. The structures in the higher HCO+ column density sample have higher temperatures and are found in directions with more thermally unstable HI than the structures in the lower HCO+ column density sample. We have recently observed SiO in the direction of several of these structures to investigate the role of shocks in enhancing molecule formation and test the validity of the PDR models in these environments.

Remote Talk: Detection of Cosmological 21cm Emission with CHIME

Simon Foreman (Perimeter Institute, CHIME)

Intensity mapping of redshifted 21cm emission from neutral hydrogen holds great promise for learning about cosmology, as it provides an efficient way to map large volumes of the universe without the need to characterize individual luminous sources. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) was custom-built for this purpose, with additional science targets including fast radio bursts, pulsars, and Galactic radio emission. In this talk, I will place the telescope’s design in the context of its cosmology science case, and then present its first 21cm science results: detection of a cross-correlation between CHIME sky maps and galaxy/quasar catalogs from the extended Baryon Oscillation Spectroscopic Survey (eBOSS). In particular, I will discuss key aspects of our data processing pipeline and how we model the measured signal, as well as the physical implications and prospects for more precise future measurements.

Remote Talk: Do discs allow the planets get close to their host stars?

Sareh Ataiee (Ferdowsi University of Mashhad)

Orbital distribution of over 4000 confirmed exoplanets indicates a population of super-Earth planets close to their host stars. If an inward disc-driven migration scenario is assumed for their formation, these planets could have been stopped and parked at an inner edge of the disc, or be pushed through the inner disc cavity by a resonant chain. I will briefly explain how we investigate this topic using hydrodynamical simulations, under what condition the planets can get close to their parent stars, and one missing piece in the theory of planetary migration.

Remote Talk: Magnetohydrodynamic Turbulence in the ISM

James Stone (Institute for Advanced Study)

The structure and dynamics of dense, cold molecular gas in the ISM from which star form is strongly affected by supersonic magnetohydrodynamic (MHD) turbulence. Numerical methods have allowed exploration of the full nonlinear regime of such turbulence and have provided many important insights. I will review recent results from numerical MHD studies of supersonic MHD turbulence on both small (parsec) scales that investigate the statistics and decay rate of turbulence, as well as global (kiloparsec) scales that investigate mechanisms that drive turbulence (such as e.g., supernovae, galactic shear, and outflows) as well as how molecular clouds form. I will highlight a few key results from such studies, and discuss future directions.

Remote Talk: Pulsar Timing Arrays CHIME in on Gravitational Waves

Deborah Good (University of Connecticut, CHIME)

In the 55 years since their discovery, pulsars (rapidly rotating and highly magnetized neutron stars) have been exciting physics laboratories. In particular, the impressive stability of millisecond pulsar rotations has made them powerful probes of gravity and now allows us to use pulsar timing datasets as Galactic-scale gravitational wave detectors. In this talk, I’ll provide a broad overview of the state of pulsar timing array science, including our current progress towards detecting the stochastic gravitational wave background from supermassive black hole mergers, the contributions of CHIME/Pulsar to PTA science, and ongoing work towards a third International Pulsar Timing Array dataset.

Remote Talk: Precision Galactic magnetometry through dust polarization

Raphael Skalidis (University of Crete, Greece & Institute of Astrophysics)

Dust polarization is used to probe the magnetic field properties in the interstellar medium (ISM), but it does not provide a direct measurement of its strength. The method developed by Davis 1951, Chandrasekhar and Fermi 1953 (DCF) employs dust polarization and spectroscopic data in order to infer the magnetic field strength. This method relies on the assumption that the observed linewidths of the emission spectra and the spread in the distribution of the polarization angle is due to the propagation of incompressible waves. Observations, however, indicate that compressible waves may be important in the ISM kinematics. We have developed a new method which employs the same set of observables and takes into account the compressible waves fluctuations. We tested the two methods over a large set of magnetohydrodynamic (MHD) simulations exploring the full parameter space of the magnetized and compressible turbulence. In this presentation, I will show a comparison of the performance of the two methods, and discuss their major theoretical differences based on state-of-the-art MHD numerical simulations.