The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

TL;DR

ACTPol's two-season, night-time CMB observations at 149 GHz over 548 deg^2 yield TT, TE, and EE spectra that are consistent with $ abla$LCDM when combined with Planck/WMAP. The analysis employs flat-sky pseudo-$C__$ methods, cross-spectra, and a foreground-marginalized likelihood, plus aberration corrections and extensive null tests. The TE spectrum emerges as a powerful internal constraint on $\Omega_b h^2$, the acoustic peak angle $\theta_A$, and $H_0$, while polarization data improve damping-tail constraints when linked to Planck. These results validate LCDM predictions at small scales and demonstrate the value of ACTPol polarization in precision cosmology, with substantial gains expected from the full three-season dataset.

Abstract

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the LCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. Adding the new data to planck temperature data tightens the limits on damping tail parameters, for example reducing the joint uncertainty on the number of neutrino species and the primordial helium fraction by 20%.

Figures (25)

• Figure 1: Top (H): Exposure map in equatorial coordinates (the horizontal and vertical axes are RA and Dec respectively), including both the three-season MBAC data and the ACTPol data used in this analysis. The D5 and D6 regions are the deep fields on the right and left sides of the map, and D56 is the wider rectangle which overlaps both deep fields. The contour labels indicate the T noise level in $\mu\textrm{K}\cdot\textrm{arcmin}$, starting from $8\mu\textrm{K}\cdot\textrm{arcmin}$ in the deepest region. The Q and U noise levels are each $\sqrt{2}$ higher. Lower panels: Filtered maps in T and in Q, U, E and B-polarization. All maps are filtered with a highpass-filter at $\ell=200$ and a horizontal highpass-filter at $\ell=40$. The polarization maps are additionally lowpass-filtered at $\ell=1900$. The color scale is $\pm250\mu$K in T and $\pm25\mu$K in P.
• Figure 2: The temperature white noise levels (right axis), and inverse variance (left axis), in the ACTPol maps as a function of cumulative area. Levels are shown for the larger D56 region, the smaller D5 and D6 sub-regions, and the combined map.
• Figure 3: The beam window functions (top) and uncertainties (bottom) measured by ACTPol during the first (S1, 2013) and second (S2, 2014) observing seasons for the arrays PA1 and PA2. Both the instantaneous beams (dashed lines) and the pointing variance corrected beams (solid lines) for the three different regions included in the analysis are shown. The total solid angle and its uncertainty are given for each beam in units of nanosteradians (nsr).
• Figure 4: Polarized sidelobes in PA1 (top row) and PA2 (bottom row). Left panels show maps of the beam sidelobes, from 20 observations of Saturn. Spatial coordinates are relative the main beam, which is masked here. Grayscale provides the sidelobe amplitude in the range -0.002 (black) to +0.001 (white) relative to the main beam peak, with negative signal indicating polarization perpendicular to the ray from the origin. The complementary polarization component (corresponding to TB leakage) is smaller and not shown in the maps but is included in the evaluation of the transfer functions. Right panels show the TE and TB transfer functions, normalized in units of the main beam, as in Figure \ref{['fig:beam']}, before and after the sidelobe deprojection procedure.
• Figure 5: A 45 deg$^2$ subset of the map in full resolution in T showing ACTPol 149 GHz (top) and Planck 143 GHz (bottom), in equatorial coordinates, both filtered as in Figure 1. The color scale is $\pm250\mu$K. This region covers the transition from deep (top left, sensitivity $10\mu\textrm{K}\cdot\textrm{arcmin}$) to shallow (right, $16\mu\textrm{K}\cdot\textrm{arcmin}$) exposure, and represents about 8% of the usable area in D56. The two maps are in good agreement. Several point sources (red dots) and SZ clusters (circled) are visible in the ACTPol map. The identified clusters are ACT-CL J0137.4-0827, ACT-CL J0140.0-0554, ACT-CL J0159.8-0849 (all previously found in other cluster surveys), and ACT-CL J0205.3-0439 (reported in naess/etal:2014). Their details will be given in a forthcoming paper.