« Analyzing the millimeter to centimeter emission of nearby galaxies«
Compared to the well-studied infrared and radio domains, galaxy emission in the millimeter–centimeter range (300–30 GHz) has been far less explored. This domain is challenging to study due to faint signals, overlapping emission mechanisms, and limited instrumental coverage. My thesis addressed these challenges to provide new constraints and insights into the mm-to-cm emission of galaxies.
In this thesis, I investigated galaxy emission in this wavelength range, arising from thermal dust, free-free, and synchrotron processes, with a possible additional contribution from anomalous microwave emission (AME) peaking near 1 cm.
I characterized the integrated spectral energy distributions (SEDs) of six bright nearby galaxies (SMC, LMC, M31, M33, NGC 253, and NGC 4945) using COBE-DIRBE, IRAS, Planck, and WMAP all-sky surveys at 1° resolution, covering 97 μm to 1.3 cm, while accounting for foreground and background emissions. Modeling the mm–cm emission revealed strong degeneracies between components, which complicated the separation of their contributions. In addition, positive CMB fluctuations were inferred in the background of five of the six galaxies, likely linked to degeneracies with the dust emissivity index or to the spatial distribution of CMB fluctuations coupled with the 1° resolution and limited sample size, highlighting the need for a bigger sample of galaxies observed at better resolution. I therefore started to extend the study of mm emission to a larger sample of 22 more distant galaxies, at a higher (16′) resolution, at the cost of a decreased wavelength range.
Overall, this thesis underscored the complexity of disentangling emission mechanisms in the mm–cm range and going further will require either higher-resolution data, larger galaxy samples or redshifted galaxy studies in the radio wavelength range.