2024/09/26 by Ryan Cooke, Cooke, Ryan J., Louise Welsh +1
Physics and Astronomy · #Superconducting and THz Device Technology #Cosmology and Gravitation Theories #Radio Astronomy Observations and Technology
paper · pdf · doi:10.48550/arxiv.2409.18270
We report a new, reliable determination of the CN excitation temperature of diffuse molecular clouds in the Milky Way, based on ultra high spectral resolution observations. Our determination is based on CN B2Σ+-X2Σ+ (0,0) vibronic absorption spectra seen along the lines of sight to eight bright Galactic stars. Our analysis is conducted blind, and we account for multiple sources of systematic uncertainty. Like previous studies, our excitation temperature measures exhibit an intrinsic scatter that exceeds the quoted uncertainties. Accounting for this scatter, we derive a 3% determination of the typical CN excitation temperature, T01=2.769+0.084-0.072~\rm K, which is consistent with the direct determination of the cosmic microwave background temperature. We also perform a single joint fit to all sightlines, and find that our data can be simultaneously fit with an excitation temperature T01=2.725±0.015~\rm K -- a 0.55% measure that is consistent with the CMB temperature. We propose a future observational strategy to reduce systematic uncertainties and firmly test the limitations of using CN as a cosmic microwave background thermometer.