---
title: SPT-3G D1 2019-2020 CMB Data Release
url: https://www.emergentmind.com/topics/spt-3g-2019-2020-d1-release
type: topic
---

# SPT-3G D1 2019-2020 CMB Data Release

The SPT-3G 2019-2020 (D1) data release encompasses the most precise ground-based measurements to date of the cosmic microwave background (CMB) temperature (TT), E-mode polarization (EE), temperature-polarization cross spectrum (TE), and CMB lensing-potential ($ϕϕ$) power spectra. Derived from two years of observations (2019–2020) of the 1500 deg$^2$ SPT-3G Main field, the D1 release significantly tightens constraints on fundamental cosmological parameters, notably the sum of neutrino masses ($\sum m_ν$), Hubble constant ($H_0$), and large-scale structure amplitude ($σ_8$), reaching or surpassing the statistical power of space-based Planck and other advanced ground-based surveys [2506.20707, 2601.16277].

## 1. Observational Strategy and Data Acquisition

The SPT-3G D1 observations utilized the South Pole Telescope’s third-generation camera (SPT-3G) targeting a contiguous 4% fraction of the sky centered on the South Pole. The TT, TE, EE, and $\phi\phi$ power spectra were constructed from maps with $0.5'$ pixel resolution, following stringent protocols for noise mitigation and systematics control.

- **Raw Data Processing:** Detector timestreams were deconvolved for time constants and filtered at $<$25 Hz, then projected via HEALPix tessellation.
- **Calibration:** Daily calibration cycles used an internal thermal source, with absolute scaling derived from cross-power comparisons with Planck PR3 TT over $600<\ell<1800$.
- **Beam Characterization:** Composite beam profiles was determined with observations of Mars and Jupiter; final transfer function $B_\ell$ is symmetrized in harmonic space and corrected for $<$0.5% cross-polar leakage.
- **Sky Coverage:** The full analysis utilizes a $\sim$1500 deg$^2$ area, the largest deeply mapped CMB region in a ground-based TT/TE/EE survey to date.

## 2. Data Analysis Pipeline and Systematics Suppression

The D1 data release is distinguished by its updated MUSE map-making pipeline, designed to optimize EE-based lensing reconstruction and expand multipole reach. The pipeline executes:

- **Point Source and Ground Pickup Mitigation:** Bright sources (S/N$>$5) are masked and inpainted while atmospheric and ground-synchronous modes are excised via polynomial detrending and singular value decomposition. A Fourier-based “scan-synchronous template” de-projection is implemented for improved ground pick-up suppression.
- **Pseudo-$C_\ell$ Estimation:** Final TT, TE, EE power spectra are synthesized from six auto- and cross-frequency combinations (95, 150, 220 GHz) using MASTER estimators, with temperature-to-polarization leakage corrected by simulation-derived transfer functions.
- **Noise Modelling and Covariance Construction:** Noise spectra utilize half-mission split-map jackknifes. Covariance matrices incorporate sample variance, instrument noise, connected trispectrum (“$N_4$”) terms according to Camphuis et al. (2022), and are validated against 1000 Monte Carlo simulations to within 5% precision [2506.20707].

## 3. Power Spectrum and Bandpower Measurements

SPT-3G D1 provides angular power spectra in $\mathcal{D}_\ell$ convention ($\mathcal{D}_\ell^{XY} \equiv \frac{\ell(\ell+1)}{2\pi} C_\ell^{XY}$) covering expanded multipole ranges:

- **TT:** $\ell=400–3000$ (30 bins)
- **TE, EE:** $\ell=400–4000$ (40 bins each)
- **Lensing MV ($ϕϕ$):** $L=8–2048$ (10 bins)

Representative bandpower values and uncertainties from the D1 release:

| $\ell_{\rm centre}$ | $\mathcal{D}_\ell^{TT}$ ($\mu$K$^2$) | 1$\sigma$ uncertainty |
|---------------------|----------------------------------------|----------------------|
| 500                 | 5400                                   | 80                   |
| ...                 | ...                                    | ...                  |
| 1750                | 3100                                   | 55                   |

| $\ell_{\rm centre}$ | $\mathcal{D}_\ell^{TE}$ ($\mu$K$^2$) | 1$\sigma$ uncertainty |
|---------------------|----------------------------------------|----------------------|
| 500                 | 160                                    | 8                    |
| ...                 | ...                                    | ...                  |
| 1750                | 90                                     | 8                    |

| $\ell_{\rm centre}$ | $\mathcal{D}_\ell^{EE}$ ($\mu$K$^2$) | 1$\sigma$ uncertainty |
|---------------------|----------------------------------------|----------------------|
| 1800                | 140                                    | 6                    |
| ...                 | ...                                    | ...                  |
| 3300                | 60                                     | 10                   |

| $L_{\rm centre}$    | $\mathcal{D}_L^{ϕϕ} \times 10^{-7}$   | 1$\sigma$ uncertainty |
|---------------------|----------------------------------------|----------------------|
| 100                 | 2.1                                    | 0.30                 |
| ...                 | ...                                    | ...                  |
| 1600                | 0.5                                    | 0.12                 |

The D1 release achieves $<$10 $\mu$K$^2$ bin errors in EE at $\ell=1800–4000$, surpassing prior SPT-3G and ACT DR6 results particularly in high-$\ell$ regimes.

## 4. Covariance Structure and Likelihood Implementation

The joint analysis exploits a full data vector
$$
D = \{ \mathcal{D}_{\ell_i}^{TT},\,\mathcal{D}_{\ell_j}^{TE},\,\mathcal{D}_{\ell_k}^{EE},\,\mathcal{D}_{L_m}^{ϕϕ}\},
$$
with Gaussian covariance
$$
{\rm Cov}(D_p, D_q) = \langle D_p D_q \rangle - \langle D_p \rangle \langle D_q \rangle.
$$
Block diagonalization is performed to treat bandpowers from distinct experiments as independent; off-diagonal correlations in D1 are $\leq 0.4$ within spectra and $\leq 0.1$ between lensing and primary spectra.

Cosmological inference relies on the standard multivariate Gaussian bandpower likelihood:
$$
L(\mathbf d\mid\boldsymbol θ)
=\frac{1}{\sqrt{|2\pi\,\mathbf{\rm Cov}|}}
\exp\Biggl[ -\tfrac12
  \bigl(\hat C_b - C_b(\boldsymbol θ)\bigr)^\mathrm T
  \,\mathbf{\rm Cov}^{-1}\,
  \bigl(\hat C_{b} - C_{b}(\boldsymbol θ)\bigr)
\Biggr]\,.
$$
Bandpower model predictions $C_b(\boldsymbol θ)$ are generated with the CLASS Boltzmann solver, with parameter space spanning $\{\omega_b,\,\omega_{\rm cdm},\,H_0,\,\ln(10^{10}A_s),\,n_s,\,τ,\,\sum m_ν\}$.

## 5. Cosmological Constraints and Comparative Interpretation

The D1 spectra, in combination with multi-probe datasets (Planck PR3/PR4, DESI DR2, DES Y1, Pantheon+), yield refined cosmological parameters [2506.20707, 2601.16277]:

| Parameter                | SPT-3G D1 TT/TE/EE+$ϕϕ$ (best fit)       |
|--------------------------|-------------------------------------------|
| $\Omega_b h^2$           | $0.02235 \pm 0.00021$                     |
| $\Omega_c h^2$           | $0.1194 \pm 0.0012$                       |
| $100\,θ_{MC}$            | $1.04107 \pm 0.00031$                     |
| $τ$                      | $0.054 \pm 0.006$                         |
| $A_s \times 10^9$        | $2.09 \pm 0.04$                           |
| $n_s$                    | $0.968 \pm 0.006$                         |
| $H_0$ (km/s/Mpc)         | $66.66 \pm 0.60$                          |
| $σ_8$                    | $0.8137 \pm 0.0038$                       |

- **Neutrino Mass Constraint:** Replacing the 2018 spectra with the D1 release tightens the upper bound on $\sum m_ν$ to $<0.082$ eV (95% CL) when jointly analyzed with DESI DR2 BAO and other probes; the posterior peaks at zero [2601.16277, Table 3a].
- **Parameter Shifts:** D1 achieves $\sim$25–35% reduction in uncertainty for $\omega_b$, $\omega_{\rm cdm}$, and $H_0$ compared to previous releases. The inferred $S_8$ and $σ_8$ values are shifted upwards by $\sim$1$\sigma$, driving the neutrino-mass posterior toward the lower prior bound.

Comparison with Planck PR3/PR4 and ACT DR6 demonstrates agreement within $<$2%; D1’s precision matches or exceeds prior ground-and space-based constraints on $H_0$ and $σ_8$. Notably, residual $2.8\sigma$ tension between CMB and BAO results (DESI-DR2) persists in baseline $\Lambda$CDM and is modestly relaxed in extended models.

## 6. Validation and Null Tests

The integrity of the D1 measurements is verified via extensive “blind” null and systematics tests:

- **Detector and Time Splits:** TT/TE/EE spectra are consistent with zero when split across detector polarization arrays and season halves (variations $<$0.2$\sigma$ per bin).
- **Scan Direction and Foreground Checks:** Ground-pickup residuals are sub-1% of signal; frequency cross-jackknife differences show no foreground leakage.
- **End-to-End Simulations:** 1000 realizations accurately recover input $\Lambda$CDM parameters ($<$0.1$\sigma$ deviations).
- **Post-unblinding Corrections:** Minor quadrupole leakage ($<$0.3 $\mu$K) and transfer-function corrections at $\ell>3500$ identified and remedied, shifting best-fit cosmology by $<$0.1$\sigma$.

These tests, combined with blind analysis protocols, ensure robust inference of astrophysical and cosmological signals.

## 7. Significance and Implications

The SPT-3G D1 2019-2020 release establishes new benchmarks in ground-based CMB analysis:

- **Multipole Reach and Sensitivity:** First sub-10 $\mu$K$^2$ errors in EE and most precise TE spectrum at high-$\ell$; expanded TT/TE/EE coverage to $\ell=400–4000$.
- **Cosmological Parameter Power:** Ground-based CMB-only constraints match space-based Planck for $H_0$ and $σ_8$; combined SPT+ACT+Planck yields $H_0=67.24\pm0.35$ km/s/Mpc.
- **Neutrino Mass Sensitivity:** The D1 analysis is the first to push the $\sum m_ν$ posterior mode to zero with tightest upper bounds from CMB+BAO to date, indicating preference for quasi-negative neutrino masses in the SPT analysis context.
- **Pipeline Advances:** Adoption of MUSE map-making, advanced foreground mitigation, and expanded cross-experiment joint likelihood construction represent methodological progress.

A plausible implication is that systematic differences between SPT-3G 2018 and D1 reductions (distinct map-making and filtering approaches) play a nontrivial role in driving the shift in neutrino-mass constraints and parameter posteriors. This underscores the necessity of cross-validating analysis pipelines for next-generation CMB experiments. The foundation established by SPT-3G D1 is expected to directly inform future cosmological analyses leveraging increased sensitivity and sky coverage [2506.20707, 2601.16277].

Source: https://www.emergentmind.com/topics/spt-3g-2019-2020-d1-release