The Simons Observatory: Assessing the Impact of Dust Complexity on the Recovery of Primordial $B$-modes
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| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Liu, Yiqi Azzoni, Susanna Clark, Susan E. Hensley, Brandon S. Vacher, Léo Alonso, David Baccigalupi, Carlo Brown, Michael L. Carones, Alessandro Chluba, Jens Dunkley, Jo Hervías-Caimapo, Carlos Johnson, Bradley R. Krachmalnicoff, Nicoletta Puglisi, Giuseppe Remazeilles, Mathieu Wolz, Kevin |
| author_facet | Liu, Yiqi Azzoni, Susanna Clark, Susan E. Hensley, Brandon S. Vacher, Léo Alonso, David Baccigalupi, Carlo Brown, Michael L. Carones, Alessandro Chluba, Jens Dunkley, Jo Hervías-Caimapo, Carlos Johnson, Bradley R. Krachmalnicoff, Nicoletta Puglisi, Giuseppe Remazeilles, Mathieu Wolz, Kevin |
| contents | We investigate how dust foreground complexity can affect measurements of the tensor-to-scalar ratio, $r$, in the context of the Simons Observatory, using a cross-spectrum component separation analysis. Employing a suite of simulations with realistic Galactic dust emission, we find that spatial variation in the dust frequency spectrum, parametrized by $β_d$, can bias the estimate for $r$ when modeled using a low-order moment expansion to capture this spatial variation. While this approach performs well across a broad range of dust complexity, the bias increases with more extreme spatial variation in dust frequency spectrum, reaching as high as $r\sim0.03$ for simulations with no primordial tensors and a spatial dispersion of $σ(β_d)\simeq0.3$ -- the most extreme case considered, yet still consistent with current observational constraints. This bias is driven by changes in the $\ell$-dependence of the dust power spectrum as a function of frequency that can mimic a primordial $B$-mode tensor signal. Although low-order moment expansions fail to capture the full effect when the spatial variations of $β_d$ become large and highly non-Gaussian, our results show that extended parametric methods can still recover unbiased estimates of $r$ under a wide range of dust complexities. We further find that the bias in $r$, at the highest degrees of dust complexity, is largely insensitive to the spatial structure of the dust amplitude and is instead dominated by spatial correlations between $β_d$ and dust amplitude, particularly at higher orders. If $β_d$ does spatially vary at the highest levels investigated here, we would expect to use more flexible foreground models to achieve an unbiased constraint on $r$ for the noise levels anticipated from the Simons Observatory. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2508_00073 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Simons Observatory: Assessing the Impact of Dust Complexity on the Recovery of Primordial $B$-modes Liu, Yiqi Azzoni, Susanna Clark, Susan E. Hensley, Brandon S. Vacher, Léo Alonso, David Baccigalupi, Carlo Brown, Michael L. Carones, Alessandro Chluba, Jens Dunkley, Jo Hervías-Caimapo, Carlos Johnson, Bradley R. Krachmalnicoff, Nicoletta Puglisi, Giuseppe Remazeilles, Mathieu Wolz, Kevin Cosmology and Nongalactic Astrophysics We investigate how dust foreground complexity can affect measurements of the tensor-to-scalar ratio, $r$, in the context of the Simons Observatory, using a cross-spectrum component separation analysis. Employing a suite of simulations with realistic Galactic dust emission, we find that spatial variation in the dust frequency spectrum, parametrized by $β_d$, can bias the estimate for $r$ when modeled using a low-order moment expansion to capture this spatial variation. While this approach performs well across a broad range of dust complexity, the bias increases with more extreme spatial variation in dust frequency spectrum, reaching as high as $r\sim0.03$ for simulations with no primordial tensors and a spatial dispersion of $σ(β_d)\simeq0.3$ -- the most extreme case considered, yet still consistent with current observational constraints. This bias is driven by changes in the $\ell$-dependence of the dust power spectrum as a function of frequency that can mimic a primordial $B$-mode tensor signal. Although low-order moment expansions fail to capture the full effect when the spatial variations of $β_d$ become large and highly non-Gaussian, our results show that extended parametric methods can still recover unbiased estimates of $r$ under a wide range of dust complexities. We further find that the bias in $r$, at the highest degrees of dust complexity, is largely insensitive to the spatial structure of the dust amplitude and is instead dominated by spatial correlations between $β_d$ and dust amplitude, particularly at higher orders. If $β_d$ does spatially vary at the highest levels investigated here, we would expect to use more flexible foreground models to achieve an unbiased constraint on $r$ for the noise levels anticipated from the Simons Observatory. |
| title | The Simons Observatory: Assessing the Impact of Dust Complexity on the Recovery of Primordial $B$-modes |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2508.00073 |