# The Atacama Cosmology Telescope: likelihood for small-scale CMB data

**Authors:** J. Dunkley, E. Calabrese, J. Sievers, G. E. Addison, N. Battaglia, E. S. Battistelli, J. R. Bond, S. Das, M. J. Devlin, R. Dunner, J. W. Fowler, M. Gralla, A. Hajian, M. Halpern, M. Hasselfield, A. D. Hincks, R. Hlozek, J. P. Hughes, K. D. Irwin, A. Kosowsky  
**arXiv:** [1301.0776](https://arxiv.org/abs/1301.0776)  
**Date:** 2013-01-04  
**Summary page:** https://www.summarizepaper.com/en/paper/1301.0776v2/

## Key points

- The Atacama Cosmology Telescope (ACT) conducted extensive measurements of microwave fluctuations at 148 and 218 GHz frequencies over three seasons.
- Data from ACT reveals angular power spectra to arcminute scales, providing insights into the primordial Cosmic Microwave Background (CMB).
- A nine-parameter model was developed to address secondary effects such as thermal and kinematic Sunyaev-Zel'dovich (tSZ and kSZ) power, Cosmic Infrared Background (CIB) sources, tSZ-CIB correlation coefficient, extragalactic radio source power, and thermal dust emission from Galactic cirrus.
- A likelihood function was formulated to extract cosmological parameters from ACT data within the multipole range of 500<ell<10000, extended to include South Pole Telescope data at 95, 150, and 220 GHz.
- Adjusting for radio sources and Galactic cirrus emission allowed the model to fit both datasets simultaneously.
- Utilizing a multi-frequency likelihood approach enabled estimation of the CMB power spectrum in bandpowers while marginalizing over secondary parameters.
- The 'CMB-only' likelihood focused on the range 500<ell<3500 for precise cosmological parameter estimation.
- The collaborative effort led by J. Dunkley provides valuable insights into small-scale CMB data and its implications for cosmology research.

## Summary

The Atacama Cosmology Telescope has conducted extensive measurements of microwave fluctuations at frequencies of 148 and 218 GHz, capturing data from three seasons. This data reveals angular power spectra to arcminute scales, shedding light on the primordial Cosmic Microwave Background (CMB). A comprehensive nine-parameter model has been developed to account for various secondary effects in order to address the challenge of obscured fluctuations at smaller scales. This includes the thermal and kinematic Sunyaev-Zel'dovich (tSZ and kSZ) power, clustered and Poisson-like power from Cosmic Infrared Background (CIB) sources with frequency scaling, tSZ-CIB correlation coefficient, extragalactic radio source power, and thermal dust emission from Galactic cirrus in different sky regions. To extract cosmological parameters from the ACT data, a likelihood function has been formulated and fitted to multi-frequency spectra within the multipole range of 500<ell<10000. The likelihood has also been extended to incorporate spectra from the South Pole Telescope at frequencies of 95, 150, and 220 GHz. By adjusting for varying levels of radio sources and Galactic cirrus emission, this same model demonstrates an excellent fit to both datasets simultaneously. Utilizing a multi-frequency likelihood approach enables estimation of the CMB power spectrum from ACT in bandpowers while marginalizing over secondary parameters. This streamlined 'CMB-only' likelihood focuses on the range 500<ell<3500 for precise cosmological parameter estimation. The collaborative effort involving a team of researchers led by J. Dunkley provides valuable insights into understanding small-scale CMB data and its implications for cosmology research.