Affiliation: University of Geneva / ESO

Contribution: Oral

Title: Characterising the spectral shapes of high-redshift MUSE Lyman-α emitters

Abstract: The Hydrogen Lyman-alpha (Lyα) line, the brightest rest-frame UV-line of high-redshift galaxies, shows a large variety of shapes which is caused by factors at different scales, from the interstellar medium to the intergalactic medium (IGM). I will present the first systematic inventory and characterisation of the spectral shapes of Lyα emission lines from a sample of 468 Lyα emitting galaxies (LAEs) between redshift 2.8–6.6. Using the unprecedented deep data from the MUSE eXtremely Deep Field (MXDF, up to 140-hour exposure time), I developed a method to classify Lyα emission lines in four spectral and three spatial categories, by combining a pure spectral analysis with a narrow-band (NB) image analysis. The method measures crucial spectral properties, such as the peak separation and the blue-to-total flux ratio (B/T) for the double-peaked galaxies, key parameters for determining gas exchanges between galaxies and their circumgalactic medium (CGM), Lya escape fraction or IGM attenuation. Among the LAE sample cleaned from observational limitations, 51% of the galaxies have a double-peak Lyα line profile. This fraction seems to be independent of luminosity and redshift. The B/T flux ratio distribution shows a majority of these double-peaks being blue-dominated (i.e., B/T>0.5), suggesting gas inflows between the CGM and their host galaxies. The high fraction of blue-dominated spectra needs to be confirmed by obtaining new systemic redshift measurements.
Looking at the Lyα NB images, around 20% of the sample lies in a complex environment, meaning there are other clumps or galaxies at the same redshift within a distance of 30 kpc. Those configurations of interacting galaxies are known to enhance star formation. My results highlight the importance of considering both the spectral and spatial information of a galaxy to state the nature of the observed Lyα lines and thus use them to give physical interpretations. Statistical samples of double-peaks are a promising probe of the evolution of the physical properties of galaxies across cosmic time.

This contribution can be found here (pdf).