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Spectral shapes of the Lyman-alpha emission from galaxies: I. blueshifted emission and intrinsic invariance with redshift | | Matthew J. Hayes
; Axel Runnholm
; Max Gronke
; Claudia Scarlata
; | | Date: |
5 Jun 2020 | | Abstract: | We demonstrate the redshift-evolution of the spectral profile of HI
Lyman-alpha (Ly{alpha}) emission from star-forming galaxies. In this first
study we pay special attention to the contribution of blueshifted emission. At
redshift z=2.9-6.6, we compile spectra of a sample of 229 Ly{alpha}-selected
galaxies identified with the Multi-Unit Spectroscopic Explorer at the Very
Large Telescope, while at low-z (< 0.44) we use a sample of 74
ultraviolet-selected galaxies observed with the Cosmic Origin Spectrograph
onboard the Hubble Space Telescope. At low-z, where absorption from the
intergalactic medium (IGM) is negligible, we show that the relative
contribution of blueshifted emission (blue/red) increases rapidly with
increasing equivalent width ($W_{Ly{alpha}}$). This result does not, however,
emerge at z=3-4, and we use bootstrap simulations to demonstrate the blue
emission to be suppressed by stochastic IGM absorption. Our main result is that
the blue-peak contribution evolves rapidly downwards with increasing redshift:
the blue/red flux ratio is $approx 30$% at $zapprox 0$, but drops to 15% at
$zapprox 3$, and to below 3% by $zapprox 6$. Applying further simulations of
the IGM absorption to the unabsorbed COS spectrum, we demonstrate that this
decrease in the blue-wing contribution can be entirely attributed to the
thickening of intervening Ly{alpha} absorbing systems, with no need for
additional HI opacity from local structure, companion galaxies, or cosmic
infall. We discuss our results in light of the numerical radiative transfer
simulations, the evolving total Ly{alpha} output of galaxies, and the utility
of resolved Ly{alpha} spectra in the reionization epoch. | | Source: | arXiv, 2006.3232 | | Services: | Forum | Review | PDF | Favorites | |
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