Research

At far-infrared wavelengths the angular resolution of a single telescope is limited by diffraction. The 3.5 m primary mirror of Herschel resolved only about 7″ at 100 µm, and deep far-infrared surveys are limited by source confusion. Interferometry overcomes this limit by combining light collected by separated apertures.

Double-Fourier interferometry combines spatial interferometry with Fourier transform spectroscopy, so that a single scanning instrument records a spectrum at every point of a high-resolution image (Figure 1). The group has built a far-infrared double-Fourier laboratory testbed to develop and verify the measurement and data-processing techniques that a space interferometer will require, including phase calibration, complex visibility measurement and image reconstruction.

Far-infrared detectors must be cooled to a fraction of a kelvin to reach the sensitivity required for astronomy. The testbed uses an array of transition-edge sensor (TES) bolometers, for which the group has developed proportional–integral–derivative (PID) feedback control to stabilize the array temperature. Related work addresses the optimization of TES arrays for far-infrared astrophysics and the characterization of detector performance within the testbed.

The group contributes to studies of future far-infrared space interferometers, including the Space Interferometer for Cosmic Evolution (SPICE) concept and the SPace-based InterFerometer Feasibility (SPIFF) project. This work spans the science case, design considerations for a Great Observatory–class interferometer and publicly available end-to-end simulation tools. Group members have also contributed to the study of the Large Interferometer For Exoplanets (LIFE), a mid-infrared nulling interferometer.

A Fourier transform spectrometer (FTS) measures a spectrum by recording an interferogram as one arm of an interferometer is scanned (Figure 2). Dr. Spencer’s graduate and postdoctoral research centred on the imaging FTS of SPIRE, one of the three science instruments on the ESA Herschel Space Observatory (2009–2013). He contributed to the ground testing and calibration of the spectrometer, the assessment of its in-flight performance, and the data processing used for the mission archive.

Since 2013 the group has continued this work with the SPIRE Spectral Feature Finder, an automated tool that identifies spectral lines in the full archive of SPIRE FTS observations.

Group members have contributed to the optical and cryogenic design of the 850 GHz module for Prime-Cam on the Fred Young Submillimeter Telescope (CCAT), to a vacuum waveguide filter-bank spectrometer for far-infrared astrophysics, and to the evaluation of composite materials at cryogenic temperatures for space-based instruments.

Group members are co-authors on astrophysical studies that use far-infrared and submillimetre data. Recent examples include a measurement of the temperature of shock-heated gas in the merging cluster MACS J0717.5+3745 using relativistic corrections to the Sunyaev–Zel’dovich effect, an assessment of how accurately the luminosities of dust-obscured galaxies can be recovered from spectral energy distribution fitting, and the design of a high-resolution far-infrared survey to study the co-evolution of galaxies and supermassive black holes.

The laboratory, in the Science Commons at the University of Lethbridge, houses the far-infrared double-Fourier interferometry testbed together with its cryogenic detector system and data-acquisition electronics. The group works closely with the Astronomical Instrumentation Group, led by Dr. David A. Naylor.

Past and current collaborations