arXiv subjects

T. R. Choudhury

Publications and source records attributed to T. R. Choudhury.

5 recordsLinked to original sources

arXiv2009

Constraining cosmic reionization with quasar, gamma ray burst, and Lya emitter observations

We investigate the cosmic reionization history by comparing semi-analytical models of the Lya forest with observations of high-z quasars and gamma ray bursts absorption spectra. In order to constrain the reionization epoch z_rei, we consider two physically motivated scenarios in which reionization ends either early (ERM, z_rei>= 7) or late (LRM, z_rei~6). We analyze the transmitted flux in a sample of 17 quasars spectra at 5.7 =11 and completes at z_rei>=7, in agreement with the recent WMAP5 data.

astro-ph.CO↗

arXiv2008

The Luminosity Function of Long Gamma-Ray Bursts and their rate at z>6

We compute the luminosity function (LF) and the formation rate of long gamma ray bursts (GRBs) in three different scenarios: i) GRBs follow the cosmic star formation and their LF is constant in time; ii) GRBs follow the cosmic star formation but the LF varies with redshift; iii) GRBs form preferentially in low-metallicity environments. We then test model predictions against the Swift 3-year data, showing that scenario i) is robustly ruled out. Moreover, we show that the number of bright GRBs detected by Swift suggests that GRBs should have experienced some sort of luminosity evolution with redshift, being more luminous in the past. Finally we propose to use the observations of the afterglow spectrum of GRBs at z>5.5 to constrain the reionization history and we applied our method to the case of GRB 050904.

astro-ph↗

arXiv2008

Cosmic Radiative Feedback from Reionization

We explore the effect of cosmic radiative feedback from the sources of reionization on the thermal evolution of the intergalactic medium. We find that different prescriptions for this feedback predict quite different thermal and reionization histories. In spite of this, current data can not discriminate among different reionization scenarios. We find that future observations both from 21-cm and CMB experiments can be used to break the degeneracy among model parameters provided that we will be able to remove the foreground signal at the percent (or better) level.

astro-ph↗

arXiv2008

Glimpsing through the high redshift neutral hydrogen fog

We analyze the transmitted flux in a sample of 17 QSOs spectra at 5.74 11 Myr. The observed widths of the peaks are found to be systematically larger than the simulated ones. Reasons for such discrepancy might reside either in the photoionization equilibrium assumption or in radiative transfer effects.

astro-ph↗

arXiv2007

On the Size of HII Regions around High Redshift Quasars

We investigate the possibility of constraining the ionization state of the intergalactic medium (IGM) close to the end of reionization (z ~ 6) by measuring the size of the HII regions in high-z quasars spectra. We perform a combination of multiphase smoothed particle hydrodynamics (SPH) and 3D radiative transfer (RT) simulations to reliably predict the properties of typical high-z quasar HII regions, embedded in a partly neutral IGM (x_HI=0.1). In this work we assume a fixed configuration for the quasar lifetime and luminosity, i.e. t_Q=10^7 yr and N_gamma=5.2 10^56 s-1. From the analysis of mock spectra along lines of sight through the simulated QSO environment, we find that the HII region size derived from quasar spectra is on average 30 per cent smaller than the physical one. Additional maximum likelihood analysis shows that this offset induces an overestimate of the neutral hydrogen fraction, x_HI, by a factor of 3. By applying the same statistical method to a sample of observed QSOs our study favors a mostly ionized (x_HI < 0.06) universe at z=6.1.

astro-ph↗