The Atacama Cosmology Telescope: DR6 Maps

TL;DR

This paper presents the ACT DR6 multifrequency CMB maps (98, 150, 220 GHz) with arcminute resolution over ~19,000 deg^2, derived from 2017–2022 observations with the AdvancedACT camera. It details the end-to-end data handling, including data selection, gain and polarization calibration, pointing corrections, beam characterization, and a robust mapmaking pipeline that uses a multi-pass, noise-aware maximum-likelihood framework with bilinear P, cut-sample modeling, and model-error mitigation. The work introduces depth-1 maps for time-domain studies, NILC-based ILC maps for component separation, and a comprehensive suite of DR6 products (night-time maps, depth-1 maps, Planck coadds, and null tests), along with thorough discussions of correlated noise, transfer function biases, and pickup contamination. The DR6 dataset significantly improves depth and coverage relative to prior releases, enabling cross-correlation studies with major surveys and setting the stage for future DR7 expansions including new low-frequency bands. Data are publicly available via LAMBDA and an interactive atlas, supporting wide use in cosmology and multi-wavelength analyses.

Abstract

We present Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) maps of the Cosmic Microwave Background temperature and polarization anisotropy at arcminute resolution over three frequency bands centered on 98, 150 and 220 GHz. The maps are based on data collected with the AdvancedACT camera over the period 2017--2022 and cover 19,000 square degrees with a median combined depth of 10 uK arcmin. We describe the instrument, mapmaking and map properties and illustrate them with a number of figures and tables. The ACT DR6 maps and derived products are available on LAMBDA at https://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html. We also provide an interactive web atlas at https://phy-act1.princeton.edu/public/snaess/actpol/dr6/atlas and HiPS data sets in Aladin (e.g. https://alasky.cds.unistra.fr/ACT/DR4DR6/color_CMB).

Figures (36)

• Figure 1: ACT DR6's 19 000 square degree sky coverage and its overlap with Euclid, HSC, DESI, DES and KiDS. The map is in equatorial coordinates, centered on RA=0°, dec=0°. The background map shows galactic dust intensity from Planck. See table \ref{['tab:overlaps']} for DR6' overlap with other surveys.
• Figure 2: The state of the art for EE power spectrum measurements, illustrated using the signal-to-uncertainty ratio per $\Delta \ell=1$ bin on the right axis (non-equispaced) and its square, the constraining power, on the left axis (equispaced). When plotted this way, the areas under the curves are proportional to each survey's inverse variance for the overall EE spectrum amplitude. Where not cosmic variance limited, the curves grow proportionally with integration time, so for example Planck would need to integrate for 3x as long to match ACT DR6 at $\ell=1000$. The curves show Planck planck_2018_overview, the SPT-3G 2018 data release spt-spectrum-2018 and ACT DR4 act-dr4-spectrum, as well as our new result (violet) and an estimate for the potential of a future analysis that adds the DR6 day-time data (dotted violet).
• Figure 3: AdvancedACT's five bandpasses normalized to a peak of 1. DR6 is based on f090, f150 and f220. We postpone the lowest two bands, which were installed in 2020, for future work.
• Figure 4: PA6 f090 maps without (left) and with (middle) model error mitigation in high-contrast areas, along with their difference (right). The view is centered on bright quasar 3C 273, which has an f090 flux of 12 Jy and a peak amplitude of 110 mK with the PA6 beam. The maps are plotted with a $\pm500$ µK color range (dark blue to dark red), with RA and dec on the horizontal and vertical axes. Without model error mitigation an X-shaped pattern with a typical amplitude of 100 µK (0.1% of the peak) appears around the quasar, extending out around $3\degree$ in each direction.
• Figure 5: The ACT DR6 survey area in equatorial coordinates, with RA on the horizontal axis and dec on the vertical. The colored contours show the total day+night (top) and night-only (bottom) pan-frequency depth in steps of 1 $\micro$K arcmin, going from 4 $\micro$K arcmin (dark red) to 17 $\micro$K arcmin (dark blue). Some contour lines are labeled for convenience. About half the day-time data are concentrated in the regions labeled "Day-N" and "Day-S". The rest are spread out over the whole area like the night-time data are. See figure \ref{['fig:cumrms-T-perfreq']} for how the individual frequencies compare, but typically f090/f150/f220 values are 1.41/1.45/6.6 times higher. The outermost dark red line shows the edge of the exposed area. The dust-dominated Planck 353 GHz map is shown in grayscale in the background.