COMAP and ACT are both currently mapping the 30 GHz sky at similar resolution - 4.5 arcmin FWHM for COMAP and 7.0 arcmin FWHM for ACT. COMAP's primary focus is to study the highly redshifted CO sky at high spectral resolution, but it has also been conducting a 26-34 GHz continuum survey of the Milky Way since June 2019. Early results of this were published in COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey (2021-11-10), which included a preliminary map of the galaxy for -2°<lat<2° and 20°<lon<40°.
ACT installed a new low-frequency array including detectors sensitive to a broad band centered on 27 GHz in 2020, and has been collecting usable data at these frequencies since August 2020. Like COMAP, ACT does not focus on the Milky Way, but the area with -10°<lon<56° and 189°<lon<252° is still hit at varying levels.
Since the two survey's areas overlap, it's interesting to compare what they see. To do this I projected the ACT map onto the COMAP patch at 1 arcmin CAR pixelization, and scaled the COMAP image from the paper to the same pixel size. I also recolored the COMAP image to match the Planck colormap we use in ACT to make the comparison easier. The result is shown below (or click here for an animated gif that flips between them):
| COMAP | |
|---|---|
| ACT | |
Like the COMAP map, the ACT map is preliminary, but overall the agreement is good. Both ACT and COMAP have some large-scale noise and/or bias, but the smaller details agree nicely. The COMAP map is noticably sharper, as expected from its 36% smaller beam, but ACT has lower noise. The ACT small-scale noise level varies from around 0.3 mK arcmin to 1 mK arcmin over this area, with the center being deepest. For comparison, COMAP has a noise level of 5 mK arcmin to 15 mK arcmin.
Once the COMAP galactic survey finishes in 2023/2024 it will be useful to do a systematic comparison of the two, since their different scanning patterns and detector technologies mean they should have different systematic errors.