Abstract Details
| Name: Prakash Gaikwad Affiliation: NCRA-TIFR, Pune Conference ID: ASI2019_104 Title : Efficient simulations of the intergalactic medium and parameter estimation Authors and Co-Authors : Prakash Gaikwad (NCRA-TIFR Pune, KICC-IoA Cambridge UK), Tirthankar Roy Choudhury (NCRA-TIFR Pune), Raghunathan Srianand (IUCAA Pune), Vikram Khaire (UCSB, USA) Abstract Type : Oral Abstract Category : Thesis Abstract : The IGM at $z\leq2.5$ is highly ionized due to uniform ultra-violet background (UVB) contributed by quasars and galaxies. An accurate characterization of the UVB is necessary for modeling the physical conditions of IGM, ionization corrections to derive metallicities and census of baryons. In this work we constraints the HI photoionization rate ($\Gamma_{\text{HI}}$) at $z<0.5$ using unprecedented quality HST-COS Ly-$\alpha$ forest spectra towards 82 QSOs. Simulations of high-$z$ Ly-$\alpha$ forest show a tight correlation between temperature and density. At low-$z$ it is shown that due to different physical processes such as shock heating, various feedback processes, turbulence and radiative cooling the effective equation of state can get modified appreciably. We present a new semi-numerical method (using Gadget-2) for evolution of IGM temperature from high-$z$ to low-$z$. The resultant thermal history is consistent with other low-$z$ simulations in the past. Our method is computationally less expensive and it allows us to explore a large parameter space. The Ly-$\alpha$ forest spectra generated from this simulation is remarkably similar to the observed spectra. We compare simulated Ly-$\alpha$ forest with observations using flux probability distribution function, flux power spectrum and column density distribution function. We obtained the best fit $\Gamma_{\text{HI}}$ and associated error using proper statistical analysis taking into account the appropriate co-variance matrix. Our result shows that the thermal history parameters, metallicity and turbulence do not have strong influence on the derived photoionization rate. Using the cosmological radiative transfer code we find that our new constraints on $\Gamma_{\text{HI}}$ are consistent with very low escape fraction found in low-$z$ galaxies and contrary to the recent claims of photon underproduction crisis. |