2006.03232
Spectral shapes of the Lyman-alpha emission from galaxies: I. blueshifted emission and intrinsic invariance with redshift
Hayes, et al
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 $z\approx 0$, but drops to 15% at $z\approx 3$, and to below 3% by $z\approx 6$. 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.
Spectral shapes of the Lyman-alpha emission from galaxies: I. blueshifted emission and intrinsic invariance with redshift
Hayes, et al
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 $z\approx 0$, but drops to 15% at $z\approx 3$, and to below 3% by $z\approx 6$. 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.
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