DRAO Seminar Series Spring 2017

Time & Date Speaker Title
14:00 Fri Feb 24 Lincoln Greenhill
Harvard CFA
Cosmic Dawn
14:00 Thurs Mar 2 Roland Kothes
Radio Emission from Pulsar Wind Nebulae
9:30 Wed May 24 Rob Selina
The Next Generation Very Large Array
14:00 Wed July 5 Alec Thomson
The Australian National University
Magnetic fields of a Galactic Supershell

Cosmic Dawn

Lincoln Greenhill (Harvard CFA)

Data-driven characterization of the pre-galactic medium during Cosmic Dawn (z~15-30) via observation of the 21cm transition of Hydrogen is a frontier in cosmology. The Large Aperture Experiment to Detect the Dark Age (LEDA) is working toward measurement of sky-averaged HI absorption of the CMB at z~20, to enable inferences about the formation of stars and black holes in dark matter haloes before Reionization. LEDA is a unique joint application of single-antenna radiometry and interferometric calibration. In general this type of system is also suited to measurement of spatial-fluctuation power spectra. After discussing LEDA, lessons learned, and recent results, I will introduce a proposed instrument intended for power spectrum measurement up to z~27 and the epoch of Lya-coupling, for which inferences drawn from 21cm signal will bear more on physical and less on astrophysical processes.

Radio Emission from Pulsar Wind Nebulae

Roland Kothes (DRAO)

Fast rotating neutron stars produce a steady energetic wind of relativistic particles and magnetic field that is released into the expanding ejecta of a supernova explosion. This pulsar wind creates a nebula, in which the relativistic particles travel through the magnetic field producing synchrotron emission observable from radio to the Gamma-ray band. In the radio band, smooth, highly linearly polarized emission arises from well ordered magnetic fields that can be characterized by a power-law distribution of flux. In this review I will summarize properties and evolution of pulsar wind nebulae and present the characteristics of the radio emission that we observe. I will derive magnetic field configurations and discuss their impact on overall PWN models.

The Next Generation Very Large Array

Rob Selina (NRAO)

An overview of the next generation Very Large Array (ngVLA) project, an interferometric array with 10 times greater effective collecting area and spatial resolution than the current VLA and ALMA, optimized for operation in the 0.3cm to 3cm range.

The Next Generation Very Large Array 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 unprecedented broad band continuum polarimetric imaging of non-thermal processes.

I will present preliminary performance specifications for the instrument, technical issues under study, recent activities, and upcoming milestones.

Magnetic fields of a Galactic Supershell

Alec Thomson (ANU)

Magnetic fields are known to play a crucial role in the interstellar medium (ISM) of the Galaxy. Radio polarimetry provides an excellent method of measuring magnetic fields in the ISM. Galactic supershells are some of the largest structures in the Galactic ISM, and should perturb the structure of Galactic magnetic fields. I will present my work determining the structure and strength of magnetic fields associated with a Galactic supershell. This was achieved by modelling the effect of the magnetic fields on polarised radio continuum emission, and fitted using maximum likelihood techniques.