The effects of the small-scale DM power on the cosmological neutral hydrogen (HI) distribution at high redshifts

Sarkar, Abir and Mondal, Rajesh and Das, Subinoy and Sethi, Shiv K and Bharadwaj, Somnath and Marsh, David J E (2016) The effects of the small-scale DM power on the cosmological neutral hydrogen (HI) distribution at high redshifts. In: JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (4).

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Abstract

The particle nature of dark matter remains a mystery. In this paper, we consider two dark matter models - Late Forming Dark Matter (LFDM) and Ultra-Light Axion (ULA) models - where the matter power spectra show novel effects on small scales. The high redshift universe offers a powerful probe of their parameters. In particular, we study two cosmological observables: the neutral hydrogen (HI) redshifted 21-cm signal from the epoch of reionization, and the evolution of the collapsed fraction of HI in the redshift range 2 < z < 5. We model the theoretical predictions of the models using CDM-like N-body simulations with modified initial conditions, and generate reionization fields using an excursion set model. The N-body approximation is valid on the length and halo mass scales studied. We show that LFDM and ULA models predict an increase in the HI power spectrum from the epoch of reionization by a factor between 2-10 for a range of scales 0.1 <k < 4 Mpc(-1). Assuming a fiducial model where a neutral hydrogen fraction (x) over bar (HI) = 0.5 must be achieved by z = 8, the reionization process allows us to put approximate bounds on the redshift of dark matter formation z(f) > 4 x 10(5) (for LFDM) and the axion mass m(a) > 2.6 x 10(-23) eV (for ULA). The comparison of the collapsed mass fraction inferred from damped Lyman-alpha observations to the theoretical predictions of our models lead to the weaker bounds: z(f) > 2 x 10(5) and m(a) > 10(-23) eV. These bounds are consistent with other constraints in the literature using different observables; we briefly discuss how these bounds compare with possible constraints from the observation of luminosity function of galaxies at high redshifts. In the case of ULAs, these constraints are also consistent with a solution to the cusp-core problem of CDM.

Item Type:	Journal Article
Publication:	JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Publisher:	IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
Additional Information:	Copy right for this article belongs to the IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	09 Mar 2017 06:40
Last Modified:	09 Mar 2017 06:40
URI:	http://eprints.iisc.ac.in/id/eprint/56370

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