The Canadian Galactic Emission Mapper: A New 8-10 GHz Telescope to Map the Polarization of the Northern Sky

@misc{maceachern2026canadian,
  title = {{The Canadian Galactic Emission Mapper: A New 8-10 GHz Telescope to Map the Polarization of the Northern Sky}},
  author = {Joshua MacEachern and Mandana Amiri and Charles L. Bennett and Guinevere Berg and Mark Halpern and Gary Hinshaw and Gordon Lacy and Thomas J. Rennie and Shuyu van Kerkwijk and Bruce Veidt and Pedro Villalba-González and Janet Weiland and Don Wiebe and Edward J. Wollack and Parham Zarei},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2608.28159},
  eprint = {2608.28159},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.28159},
}

TY  - UNPB
TI  - The Canadian Galactic Emission Mapper: A New 8-10 GHz Telescope to Map the Polarization of the Northern Sky
AU  - Joshua MacEachern
AU  - Mandana Amiri
AU  - Charles L. Bennett
AU  - Guinevere Berg
AU  - Mark Halpern
AU  - Gary Hinshaw
AU  - Gordon Lacy
AU  - Thomas J. Rennie
AU  - Shuyu van Kerkwijk
AU  - Bruce Veidt
AU  - Pedro Villalba-González
AU  - Janet Weiland
AU  - Don Wiebe
AU  - Edward J. Wollack
AU  - Parham Zarei
PY  - 2026
DA  - 2026/08/28
PB  - arXiv
DO  - 10.48550/arxiv.2608.28159
UR  - https://arxiv.org/abs/2608.28159
AB  - The Canadian Galactic Emission Mapper (CGEM) radio telescope is mapping polarized Galactic foregrounds from 8-10 GHz to aid in the search for B-modes in the Cosmic Microwave Background (CMB). Here we describe the design and early on-sky characterization of the CGEM optics. CGEM employs an on-axis, hat feed optical design that is a body of revolution (BOR) and exhibits excellent intrinsic polarization purity. We describe how we have optimized the optics with a novel framework that can directly minimize simulated intensity to polarized intensity (T→ P) leakage in angular power spectrum space. The optimized optics exhibit simulated T→ P leakage that is orders of magnitude below anticipated C_ℓ^BB for r = 10^−3 when scaled from 8-10 GHz to the CMB observing window near 95 GHz. We go on to describe the mechanical design of the optics, including a novel secondary mirror support made from Astroquartz composite that has low loss, low dielectric constant, and preserves the BOR symmetry of the optics. We then showcase the early on-sky performance of the optics with observations of the Sun and satellites, which probe the beam to 40 dB down from the peak. A beam model for the deployed CGEM optics based on electromagnetic simulations is in excellent agreement with the on-sky data.
ER  -