Understanding the redshift evolution of the luminosity functions of Lyman α emitters |
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Authors: | Saumyadip Samui Raghunathan Srianand Kandaswamy Subramanian |
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Affiliation: | IUCAA, Post Bag 4, Ganeshkhind, Pune 411 007, India |
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Abstract: | We present a semi-analytical model of star formation which explains simultaneously the observed ultraviolet (UV) luminosity function (LF) of high-redshift Lyman break galaxies (LBGs) and LFs of Lyman α emitters. We consider both models that use the Press–Schechter (PS) and Sheth–Tormen (ST) halo mass functions to calculate the abundances of dark matter haloes. The Lyman α LFs at z ≲ 4 are well reproduced with only ≲10 per cent of the LBGs emitting Lyman α lines with rest equivalent width greater than the limiting equivalent width of the narrow band surveys. However, the observed LF at z > 5 can be reproduced only when we assume that nearly all LBGs are Lyman α emitters. Thus, it appears that 4 < z < 5 marks the epoch when a clear change occurs in the physical properties of the high-redshift galaxies. As Lyman α escape depends on dust and gas kinematics of the interstellar medium (ISM), this could mean that on an average the ISM at z > 5 could be less dusty, more clumpy and having more complex velocity field. All of these will enable easier escape of the Lyman α photons. At z > 5 , the observed Lyman α LF are well reproduced with the evolution in the halo mass function along with very minor evolution in the physical properties of high-redshift galaxies. In particular, up to z = 6.5 , we do not see the effect of evolving intergalactic medium opacity on the Lyman α escape from these galaxies. |
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Keywords: | galaxies: formation galaxies: high-redshift galaxies: luminosity function, mass function cosmology: theory early Universe |
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