Spatially-resolved Spectroscopic Analysis of Ly$\alpha$ Haloes: Radial Evolution of the Ly$\alpha$ Line Profile out to 60 kpc

TL;DR

This study uses spatially resolved spectroscopy of Ly$ ext{alpha}$ haloes around high-redshift galaxies to analyze how the Ly$ ext{alpha}$ line profile evolves with radius, revealing a systematic blueshift at large distances up to 60 kpc.

Contribution

It presents the first detailed spatially resolved analysis of Ly$ ext{alpha}$ line profiles out to 60 kpc, showing a consistent blueshift trend and providing insights into the kinematics of circumgalactic gas.

Findings

Ly$ ext{alpha}$ line peak becomes increasingly blueshifted with radius.

Blueshift reaches approximately 250 km/s at 60 kpc.

Trend observed in both mean and median stacked spectra.

Abstract

The extended Ly$\alpha$ haloes (LAHs) have been found to be prevalent around high-redshift star-forming galaxies. However, the origin of the LAHs is still a subject of debate. Spatially resolved analysis of Ly$\alpha$ profiles provides an important diagnostic. We analyse the average spatial extent and spectral variation of the circumgalactic LAHs by stacking a sample of 155 Ly$\alpha$ emitters (LAEs) at redshift $3<z<4$ in the MUSE Extremely Deep Field. Our analysis reveals that, with respect to the Ly$\alpha$ line of the target LAE, the peak of the Ly$\alpha$ line at large distances becomes increasingly more blueshifted up to a projected distance of 60 kpc ($\approx 3 \times$ virial radius), with a velocity offset of $\approx$ 250 km/s. This trend is evident in both the mean and median stacks, suggesting that it is a general property of our LAE sample, which typically has a Ly$\alpha$ luminosity $\mathrm{\approx 10^{41.1} erg\,s^{-1}}$. However, due to the absence of systemic redshift data, it remains unclear whether the Ly$\alpha$ line peak at large projected distances is less redshifted compared to the inner regions or truly blueshifted with respect to the systemic velocity. We explore various scenarios to explain the large-scale kinematics of the Ly$\alpha$ line.