2009 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/332

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Author: search.filters.author.Samui, SaumyadipHas files: Yes

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    Understanding the redshift evolution of the luminosity functions of Lyman-alpha emitters
    (2009-06-01) Samui, Saumyadip; Srianand, R.; Subramanian, Kandaswamy
    We present a semi-analytical model of star formation which explains simultaneously the observed UV luminosity function of high redshift Lyman break galaxies (LBGs) and luminosity functions 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 halos. The Lyman-α luminosity functions at z . 4 are well reproduced with only . 10% 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 luminosity function 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 inter stellar 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 luminosity function 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, upto z = 6.5, we do not see the effect of evolving inter galactic medium (IGM) opacity on the Lyman-α escape from these galaxies
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    Models of high redshift luminosity functions and galactic outflows: The dependence on halo mass function
    (2009-02-01) Samui, Saumyadip; Subramanian, Kandaswamy; Srianand, R.
    The form of the halo mass function is a basic ingredient in any semi-analytical galaxy formation model. We study the existing forms of the mass functions in the literature and compare their predictions for semi-analytical galaxy formation models. Two methods are used in the literature to compute the net formation rate of halos, one by simply taking the derivative of the halo mass function and the other using the prescription due to Sasaki (1994). For the historically used Press-Schechter (PS) mass function, we compare various model predictions, using these two methods. However, as the Sasaki formalism cannot be easily generalized for other mass functions, we use the derivative while comparing model predictions of di erent mass functions. We show that the reionization history and UV luminosity function of Lyman break galaxies (LBGs) predicted by the PS mass function di ers from those using any other existing mass function, like Sheth-Tormen (ST) mass func- tion. In particular the reionization e ciency of molecular cooled halos has to be substantially reduced when one uses the ST and other mass functions obtained from the simulation instead of the PS mass function. Using 2 - minimization, we nd that the observed UV luminosity functions of LBGs at 3:0 z 7:4 are better reproduced by models using the ST mass function compared to models that use the PS mass function. On the other hand, the volume lling factor of the metals expelled from the galaxies through super- novae driven out ows di ers very little between models with di erent mass functions. It depends on the way we treat merging out ows. We also show that the porosity weighted average quantities related to the out ow are not very sensitive to the di erences in the halo mass function