Enhancing Cosmological Constraints from Foreground-Cleaned CMB Maps Using Large-Scale Structure Surveys
Abstract
Extragalactic foregrounds contaminate cosmic microwave background (CMB) temperature maps at small angular scales and limit their utility for precision cosmology. The internal linear combination (ILC) is a well-known technique for suppressing these contaminants, but residual foreground power remains a limiting factor. Kusiak et al. (2023) proposed adding galaxy number-density maps as additional ILC channels, exploiting their correlation with the large-scale structure sourcing these foregrounds to suppress contamination. Here we apply this framework to forecast the gains in CMB-based cosmological parameter constraints from near- and next-generation experiments. Using a halo-model foreground pipeline and a Fisher forecast from joint TT+TE+EE power spectra, we quantify the improvement from galaxy-tracer-assisted ILC cleaning across three configurations: enhanced Simons Observatory (SO) with unWISE or Rubin-like galaxy catalogs, and a futuristic CMB-HD configuration with a hypothetical deep galaxy survey. We find that adding galaxy tracers reduces the residual foreground power in the cleaned temperature map by ∼4%, ∼22%, and ∼32% at ℓ∼10,000 for the unWISE, Rubin-like, and futuristic samples, respectively. For the overall variance of the cleaned map at ℓ∼10,000, it provides 8%, 24%, and 17% improvements for each combination. The resulting reduction in marginalized parameter error bars is modest for the base six-parameter ΛCDM model: sub-percent for SO+unWISE, rising to ∼2% for SO+Rubin-like tracer. Including the effective number of relativistic species Neff, we find at most 2.2% improvements for both SO+Rubin-like and CMB-HD+Futuristic tracer. These results establish the expected gains from combining near-term CMB experiments with current and forthcoming large-scale-structure surveys.
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BibTeX
@misc{chen2026enhancing,
title = {{Enhancing Cosmological Constraints from Foreground-Cleaned CMB Maps Using Large-Scale Structure Surveys}},
author = {Shu-Fan Chen and J. Colin Hill},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.28487},
eprint = {2608.28487},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28487},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Enhancing Cosmological Constraints from Foreground-Cleaned CMB Maps Using Large-Scale Structure Surveys
AU - Shu-Fan Chen
AU - J. Colin Hill
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2608.28487
UR - https://arxiv.org/abs/2608.28487
AB - Extragalactic foregrounds contaminate cosmic microwave background (CMB) temperature maps at small angular scales and limit their utility for precision cosmology. The internal linear combination (ILC) is a well-known technique for suppressing these contaminants, but residual foreground power remains a limiting factor. Kusiak et al. (2023) proposed adding galaxy number-density maps as additional ILC channels, exploiting their correlation with the large-scale structure sourcing these foregrounds to suppress contamination. Here we apply this framework to forecast the gains in CMB-based cosmological parameter constraints from near- and next-generation experiments. Using a halo-model foreground pipeline and a Fisher forecast from joint TT+TE+EE power spectra, we quantify the improvement from galaxy-tracer-assisted ILC cleaning across three configurations: enhanced Simons Observatory (SO) with unWISE or Rubin-like galaxy catalogs, and a futuristic CMB-HD configuration with a hypothetical deep galaxy survey. We find that adding galaxy tracers reduces the residual foreground power in the cleaned temperature map by ∼4%, ∼22%, and ∼32% at ℓ∼10,000 for the unWISE, Rubin-like, and futuristic samples, respectively. For the overall variance of the cleaned map at ℓ∼10,000, it provides 8%, 24%, and 17% improvements for each combination. The resulting reduction in marginalized parameter error bars is modest for the base six-parameter ΛCDM model: sub-percent for SO+unWISE, rising to ∼2% for SO+Rubin-like tracer. Including the effective number of relativistic species N_eff, we find at most 2.2% improvements for both SO+Rubin-like and CMB-HD+Futuristic tracer. These results establish the expected gains from combining near-term CMB experiments with current and forthcoming large-scale-structure surveys.
ER -