Work

A determination of the cosmic microwave background temperature using Galactic molecules

Year: 2024

Type: article

Abstract: ABSTRACT We report a new, reliable determination of the cyano radical (CN) excitation temperature of diffuse molecular clouds in the Milky Way, based on ultrahigh spectral resolution observations. Our determination is based on CN $B^{2}\Sigma ^{+}-X^{2}\Sigma ^{+}$ (0, 0) vibronic band 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 per cent determination of the typical CN excitation temperature, $T_{01}=2.769^{+0.084}_{-0.072}~{\rm K}$, which is consistent with the direct determination of the cosmic microwave background (CMB) temperature. We also perform a single joint fit to all sightlines simultaneously, and find that our data can be fit with an excitation temperature $T_{01}=2.725\pm 0.015~{\rm K}$ – a 0.55 per cent 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 CMB thermometer.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stae2738

Authors: Ryan Cooke, Louise Welsh

Institutions: Durham University, Trieste Astronomical Observatory, Institute for Fundamental Physics of the Universe, University of Milano-Bicocca, National Institute for Astrophysics

Language: English

Topic: Astrophysics and Star Formation Studies

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,012

Funders: National Aeronautics and Space Administration, Durham University, Fondazione Cariplo, Science and Technology Facilities Council