Searching for helical magnetic fields in the Milky Way Galaxy

Jennifer West (UofT)

The origin and 3D structure of magnetic fields on galactic scales remains a mystery. We use solutions to the dynamo equation as a model for a galaxy’s magnetic field and simulate observations of these models as viewed from within, as is the case of the Milky Way Galaxy. These dynamo models include features such a reversals and a vertical, X-shaped component, which are motivated by previous models and observations of the Milky Way and other external galaxies. The models also include a large scale helicity that extends into the halo. We search for possible observational signatures in these models and compare to data from large scale surveys.

A next-generation Very Large Array

Eric Murphy (NRAO)

Inspired by dramatic discoveries from the Jansky VLA, VLBA, and ALMA, a plan to pursue a large collecting area radio interferometer that will open new discovery space from proto-planetary disks to distant galaxies is being developed by NRAO and the science community. Building on the superb cm observing conditions and existing infrastructure of the VLA site in the U.S. Southwest, the current vision of the ngVLA will be an interferometric array with more than 10 times the sensitivity and spatial resolution of the current VLA and ALMA, operating at frequencies spanning ~1.2. – 116 GHz with extended baselines reaching across North America. The ngVLA will be optimized for observations at wavelengths between the exquisite performance of ALMA at submm wavelengths, and the future SKA-1 at decimeter to meter wavelengths, thus lending itself to be highly complementary with these facilities. As such, the ngVLA will open a new window on the universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as deliver unprecedented broad band continuum polarimetric imaging of non-thermal processes. The ngVLA will be the only facility in the world that can tackle a broad range of outstanding scientific questions in modern astronomy by simultaneously delivering the capability to: unveil the formation of Solar System analogues; probe the initial conditions for planetary systems and life with astrochemistry; characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; use pulsars in the Galactic center as fundamental tests of gravity; and understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy.

The Dominion Astrophysical Observatory (DAO) Celebrates 100 Years of Successes

Dennis Crabtree (DAO)

The DAO was the world’s largest operating telescope when it began operation in May 1918. The 1.8-m telescope was the vision of John Stanley Plaskett who was also the first Director of the observatory. This talk will explore the 100-year history of the DAO and include many historical images and movies. It will also briefly cover the connection of the Okanagan Valley to the Plaskett family.

Zooming into the structures of planet-forming disks with ALMA

Nienke van der Marel (DAO)

In the last two decades, thousands of exoplanets, planets around other stars than our Sun, have been discovered, showing that planets are ubiquitous. However, the formation of planets itself remains a mystery. Protoplanetary disks of gas and dust around young stars are the birth cradles of planets, and analyzing their properties and structures give further insight in the planet formation process. In the year 2011, the construction of the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama desert in North Chile was completed. ALMA allows us to take very detailed observations of the cold material in protoplanetary disks through submillimeter observations of the thermal dust continuum and rotational molecular lines. Using interferometry, it is now possible to zoom in into these disks down to the scales of distances in our Solar System, while these disks are hundreds of light years away. ALMA has revolutionized our view of protoplanetary disks: rather than smooth profiles, it has turned out that disks contain gaps, rings, asymmetries and spiral arms, all indicators of active disk dynamics and recently formed planets. The observations are of such exquisite detail that they can be compared directly with predictions of hydrodynamical models of disk evolution and planet-disk interaction. Due to its high sensitivity, ALMA also allows us to do large surveys of hundreds of disks, and statistical studies can now be compared with exoplanet studies. I will show an overview of ALMA discoveries in the last few years and discuss the implications for our understanding of planet formation.

Debris disks and what they reveal about planet formation

Brenda Matthews (DAO)

The debris disk is a distinct class of object from a protoplanetary disk. While distinguishing between them is non-trivial, especially around young stars, it is clear that the dominant physical processes through which these disks evolve are very different. Debris disks represent the longest lived phase of circumstellar disks. While debris disk enthusiasts have varying definitions for the disks, broadly they can be described as collisionally-generated disks of dust (and scant amounts of gas) around main sequence and evolved stars; these disk components must be continuously replenished through collisions of larger (usually unseen) planetesimals in the system that represent the largest components of the size distribution of objects in the disk. The presence of a debris disk is a therefore a signpost that a system underwent planet formation processes and was successful at forming planetesimal scale objects. The fact that so many observed debris disks are seen to have multiple, apparently spatially distinct, components is tantalizingly suggestive that planets are also present in many of these systems.

Debris disks have been known since the era of IRAS, but they are now on a sound statistically footing, following a decade of extensive, sensitive surveys with Spitzer, Herschel and JCMT, as well as wider field surveys, such as WISE. I will broadly review the demographics of the debris disk population before discussing the current areas of most active research: high resolution imaging and modeling of substructures imaged in gas and dust with ALMA, the Gemini Planet Imager and SPHERE, and what these studies reveal about unseen planets. I will discuss the insights into the exozodiacal disk components that have been made in recent years, as well as the growing field of extreme debris disks, likely related to giant impacts in young systems. To close the loop on planet formation, I will explain why debris disks should not generally be regarded as the sites of planet formation, and I will discuss what debris disks can, and cannot tell us, about planet formation in a given system.

Exploiting Multipath Propagation

Ue-Li Pen (UToronto/CITA)

VLBI enables direct measurement of multi path propagation of Pulsars and FRBs through interstellar plasmas. These are the primary sources compact enough to emit coherent radiation which scintillates through multi-path propagation. I show initial results to probe the nature of plasma lenses, and inferred measurements of pulsar magnetospheres and FRB environments. I end with a forward look to probe space time with unprecedented precision.

CASTOR: A Flagship Canadian Space Telescope, eh?

Pat Côté (DAO)

The 2010 Long Range Plan for Canadian Astronomy noted that “Canadian space technology has reached the point that we could led a large space astronomy mission: a Canadian Space Telescope”. Since 2012, the Canadian Space Agency (CSA) has been developing a mission concept for a wide-field, nearly diffraction-limited UV/optical space telescope: the Cosmological Advanced Survey Telescope for Optical and uv Research (CASTOR). CASTOR is a 1m telescope that uses a three mirror anastigmat design to provide deep, panoramic imaging in three filters covering the 150-550nm wavelength range. In this talk, I describe the current design of the facility and highlight its extraordinary scientific potential by focusing on specific programs in cosmology and dark energy, galaxy evolution and star formation, AGNs and QSOs, near-field cosmology, Galactic structure, stellar astrophysics, exoplanets and the outer solar system.

Illuminating the Dark Universe with Radio Observations

Cynthia Chiang (McGill)

Observations of redshifted 21-cm emission of neutral hydrogen are a rapidly growing area of cosmology research. Measurements across a wide range of radio frequencies allow us to access redshifts that encompass a vast comoving volume, spanning both cosmic dawn and the formation of large-scale structure. I will describe two new experiments, HIRAX and PRIZM, that aim to shed new light on the universe’s evolution via redshifted 21-cm measurements. HIRAX is an experiment that will measure baryon acoustic oscillations (BAOs) through 21-cm intensity mapping over a frequency range of 400-800 MHz. By using the characteristic 150-Mpc BAO scale as a “ruler,” HIRAX will chart the expansion history of the universe during the period when dark energy began to dominate. The HIRAX radio telescope array will be sited in South Africa and will ultimately comprise 1024 dishes, each six meters in diameter, placed in a compact configuration. An eight-element HIRAX prototype has been constructed and is currently being commissioned. PRIZM is an experiment that is designed to study cosmic dawn by observing globally averaged 21-cm emission in a frequency range of 50-150 MHz. The instrument consists of two modified four-square antennas and a dual-polarization spectrometer back end. PRIZM deployed in April 2017 to Marion Island, an exceptionally isolated and radio-quiet location in the sub-Antarctic, and the science observations are ongoing. I will discuss the design and project status of HIRAX and PRIZM, as well as science prospects for both experiments.

CFIS-u: a blue sky for the stellar halo

Guillaume Thomas (DAO)

The stellar halo of the Milky Way is an incredible source of information, whether about the formation and the evolution of our Galaxy or to trace the Galactic potential in three dimensions. Indeed, the stellar halo is largely populated by the old metal-poor stars originally lying in satellites galaxies or globular clusters that have been disrupted by tidal effects. The spatial distribution of the different populations of the stellar halo us to reconstruct the formation history of the Milky Way, and with the advent of the Gaia DR 2, we can also use the kinematics of these stars to trace the Galactic potential at large radius.
I will present the recent result obtained with the Canada France Imaging Survey (CFIS), an ongoing CFHT Large Program that will map 10,000 deg² of the northern sky in the u-band to a depth 2.7 mag greater than SDSS and why the information added by the u-band is extremely valuable in the study of the stellar halo. With this survey, it has already been possible to trace the profile of the halo up to 220 kpc with the Blue Horizontal Branch (BHB) stars or to trace the stellar disk at a high elevation (z ~8 kpc), a possible consequence of the last passage of the Sgr dSph through the Galactic disk.

Full Mueller AW-Projection

Preshanth Jagannathan (NRAO)

Next generation radio telescope arrays are being designed and commissioned to accurately measure the polarized intensity and the rotation measures (RMs) across the entire sky through deep, wide-field radio interferometric surveys. Radio interferometric antennas are affected by direction-dependent (DD) gains due to both instrumental (antenna primary beam) and atmospheric effects (ionosphere). In my talk I will explore the consequences of these time and frequency dependent instrumental DD gains on polarimetric imaging and present the Full Mueller AW-Projection algorithm that corrects for the DD gains during interferometric imaging.

In the initial portion of my talk I will explore the effects of the DD gains of a parabolic dish antenna array on the measured polarized intensities of radio sources in interferometric images. In the latter portion of my talk I will introduce the A-Solver methodology that combines physical modeling with optimization to holographic measurements, to build an accurate model for the aperture illumination pattern. Using a parametrized ray-tracing code as the predictor, I solve for the frequency dependence of the antenna optics and show that the resulting low-order model for the VLA antenna captures the dominant frequency-dependent terms.

Steps to the Polarization Horizon

John Dickey (University of Tasmania)

At meter- and centimeter-wavelengths, the sky is dominated by Galactic synchrotron emission of cosmic rays in the Milky Way’s magnetic field. This emission is linearly polarized, but the polarization that we see is heavily influenced by Faraday rotation and depolarization by the intervening ionized medium and the line of sight magnetic field. We can study the distribution of this magneto-ionic medium by Fourier transforming the polarized brightness vs. wavelength-squared to the conjugate variable, rotation measure. This gives us the Faraday spectrum of the polarized brightness. The Faraday spectrum is in many ways analogous to the velocity spectrum of a spectral line; and it can be analyzed with the same tools, in particular the spectral moments.

The Galactic Magneto-Ionic Medium Survey (GMIMS) is the first all sky survey designed to study the Faraday spectrum of the Galactic diffuse synchrotron emission. Various telescopes are being used with broad-band cm-wave and m-wave receivers to generate the data that is needed. Curiously, although the diffuse polarization has been mapped since the 1950s, it was not until GMIMS that it was possible to compute the Faraday spectrum. This revolutionizes our study of the propagation of polarized radiation in the Milky Way, and it may make it possible to better remove the Galactic foreground from future CMB studies. The ultimate goal is to do Faraday tomography, three-dimensional mapping of the magnetic field, cosmic rays, and ionized gas in the Galaxy. But first we must understand where the polarization horizon is.