Séminaires LLR

Microwave Background Temperature at a Redshift of 6.34 from Water Absorption

par M. Pierre Cox (IAP)

Europe/Paris
salle de conférence (LLR)

salle de conférence

LLR

Description
Distortions of the observed cosmic microwave background (CMB) through the SZ effect provide direct measurements of its temperature at redshifts from 0 to 1. Additional background temperature estimates exist at higher redshifts, from 1.8 to 3.3, based on molecular and atomic line-excitation temperatures in quasar absorption-line systems. No deviations from the expected (1+z) scaling behaviour of the CMB temperature have been seen to date, but the measurements have not extended deeply into the matter-dominated area of the Universe at z>3.3. 
We will describe recent observations, obtained with NOEMA, of sub-millimetre line absorption from the water molecule against the cosmic microwave background in a massive starburst galaxy at z=6.34 (Riechers et al. 2022). These new measurements, providing the most direct constraint on Tcmb currently available at z>1, yield a temperature for the cosmic background of 16.4-30.2 K (1 sigma range) at z=6.34 that is consistent with the standard Lambda-CDM cosmology prediction. Future observations and ways to improve on this result will be briefly mentioned.