A first look at the CGM properties of typical high-z galaxies with Lya polarization
Andrea Bolamperti (MPIA, Heidelberg)
Tuesday 10/06/2025 @ 14:00, Sala Antonio Sollima (IV piano Battiferro)
Lya resonant nature makes it a challenging line to interpret: the origin of the emission and the geometry of the scattering circumgalactic medium (CGM) are still unclear. Thus far, observational efforts focused on the Lya surface brightness and spectral profile. To reproduce and interpret observations several models have been created, but widely different models provide similar spectra. The most promising frontier to disentangle them is to observe the direction and degree of polarization of the Lya emission, which significantly varies between different models. In this talk, I will focus on Abell2895a, a strongly lensed galaxy at z=3.4 composed of three star-forming clumps. I will show the rich set of ancillary data and present the results obtained from new spectropolarimetric VLT/FORS2 observations of the Lya line. I will also compare them, for the first time, with state-of-the-art polarization models. Finally, I will discuss how these results allow us to constrain the Lya photon production mechanism and the geometry of the CGM and outflows in a typical galaxy at cosmic noon and put this in the broader context of the evolution of the first galaxies.