Bayesian evidence for flux scale errors in Galactic synchrotron maps

Abstract

The 408 MHz Haslam map is widely used as a low-frequency anchor for the intensity and morphology of Galactic synchrotron emission. Multi-frequency, multi-experiment fits show evidence of spatial variation and curvature in the synchrotron frequency spectrum, but there are also poorly-understood multiplicative flux scale disagreements between experiments. We perform a Bayesian model comparison across a range of scenarios, using fits that include recent spectroscopic observations at $\sim 1$ GHz by MeerKAT as well as a reference map from the OVRO-LWA at 73 MHz. In the few square degrees that we analyzed, a large uncorrected flux scale factor potentially as large as 1.6 in the Haslam data is preferred, indicating a 60\% overestimation of the brightness. This partly undermines its use as a reference map. We also find that models with nonzero spectral curvature are statistically disfavored. Given the limited sky coverage here, we suggest a similar analysis across many more regions of the sky to determine the extent and variation of flux scale errors, and whether they should be treated as random or systematic errors in analyses that use the Haslam map as a template.

Significant changes during review -- please reread if you read the original version

References in corpus (36)

• PolyChord: nested sampling for cosmology
• PolyChord: next-generation nested sampling
• A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
• Planck 2018 results. IV. Diffuse component separation
• Planck 2015 results. IX. Diffuse component separation: CMB maps
• The Python Sky Model: software for simulating the Galactic microwave sky
• The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths
• Data Analysis for Precision 21 cm Cosmology
• An Improved Model of Diffuse Galactic Radio Emission from 10 MHz to 5 THz
• The interstellar cosmic-ray electron spectrum from synchrotron radiation and direct measurements
• All-Sky Interferometry with Spherical Harmonic Transit Telescopes
• Galactic synchrotron emission with cosmic ray propagation models
• Statistical 21-cm Signal Separation via Gaussian Process Regression Analysis
• The 21 cm Power Spectrum from the Cosmic Dawn: First Results from the OVRO-LWA
• The effect of foreground subtraction on cosmological measurements from Intensity Mapping
• The LWA1 Low Frequency Sky Survey
• The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array
• HI intensity mapping with MeerKAT: Calibration pipeline for multi-dish autocorrelation observations
• A General Bayesian Framework for Foreground Modelling and Chromaticity Correction for Global 21cm Experiments
• Simulations for single-dish intensity mapping experiments
• Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
• 21cm foregrounds and polarization leakage: a user's guide on cleaning and mitigation strategies
• Extracting HI cosmological signal with Generalized Needlet Internal Linear Combination
• Synchrotron Spectral Curvature from 22 MHz to 23 GHz
• Spectral Index of the Diffuse Radio Background Between 50 and 100 MHz
• Impact of Foregrounds on HI Intensity Mapping Cross-Correlations with Optical Surveys
• Gaussian Process Foreground Subtraction and Power Spectrum Estimation for 21 cm Cosmology
• The Second Radio Synchrotron Background Workshop: Conference Summary and Report
• Joint estimation of the Epoch of Reionization power spectrum and foregrounds
• BeyondPlanck I. Global Bayesian analysis of the Planck Low Frequency Instrument data
• Absolute Calibration of Diffuse Radio Surveys at 45 and 150 MHz
• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• The C-Band All-Sky Survey (C-BASS): Constraining diffuse Galactic radio emission in the North Celestial Pole region
• A General Bayesian Framework to Account for Foreground Map Errors in Global 21-cm Experiments
• Gain and Polarization Properties of a Large Radio Telescope from Calculation and Measurement: The John A. Galt Telescope
• Bayesian jackknife tests with a small number of subsets: Application to HERA 21cm power spectrum upper limits

Cited by in corpus (2)

• Emission-line Stacking of 21cm Intensity Maps with MeerKLASS: Inference Pipeline and Application to the L-band Deep-field Data
• Bayesian recalibration of flux scale factors in diffuse radio maps using low-resolution absolute radiometers