Lyman-alpha absorption spectrum of the primordial intergalactic medium

view Abstract Citations (99) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lyman-Alpha Absorption Spectrum of the Primordial Intergalactic Medium Bi, Hongguang Abstract We investigate and simulate Lyα absorption by the primordial hydrogen (the IGM) in the cold dark matter cosmology taking into account the Doppler effect of peculiar velocity. The IGM density is found to follow, n (x₁_) is proportional to exp (1/4πx²ᵇ_ integral e^- xb/x₁2_^ (1/x₁2_) δDM_ (x₂_) dx₂_ with δDM_ being the CDM density contrast and xb_ being the Jeans length of the IGM. Four IGM models are simulated according to their mean density OMEGAH_, temperature T, and clumping factor ξIGM (0) at the redshift range 2. 5- 3. 0. For the first model (the reference model), we take OMEGAH_ = 0. 015 h^-2^, T = 2 x 10⁴^ K, and δIGM_ = 1. 72. Random fluctuation clumps in the medium produce a forest-like Lyα absorption spectrum compatible to those observed by fitting the probability distribution function of line equivalent widths that have a mean slightly larger than 22 km s^-1^, and the two-point correlation function of the lines. Models 2 and 3 have either an increased clumping factor δIGM_ = 8102 or a decreased density OMEGAH_ = 0. 0015 h^- 2^ both of which might resemble the IGM at lower redshifts. Forest-like absorptions appear in these models too, but the total number of W >= 0. 16 A lines is decreased to 30% or 21% of model 1. Model 4 uses T = 8000 K and then produces a very noisy spectrum like those observed at higher redshifts. In order to get a reasonable Gunn-Peterson effect, we have assumed that an external UV radiation of Jc_ (13. 6 eV) = 3. 2 X 10^-21^ h^-1^ ergs^-1^ cm^-2^ Hz^-1^ (or 3. 2 X 10^-22^ h^-1^ ergs^-1^ cm^-2^ Hz^-1^ for model 3) is responsible for the ionization. Parallel nearby Lyα absorption spectra, like those of two images of a gravitationally lensed quasar, is then simulated under model 1. If the separation of the spectra is less than 20 h^-1^ kpc, they will look very similar to each other. Spectra having separations >= 200 h^-1^ kpc do not show apparent similarity, but there are still some dependences left between the forests. A time series technique (the auto- and cross- correlation coefficients) is then suggested to discriminate different IGM or Lyα cloud models and to measure the cross-dependence quantitatively. Finally, we discuss that some fundamental physical processes of the IGM neglected in the present study should follow the same dynamical behavior as in traditional cloud models; also, random clumps in the diffuse IGM can be progenitors of bound Lyα clouds formed later. The present models improve the cloud models in the sense that the linear evolved primordial IGM can also produce a forest-like Lyα absorption at high redshift, so it avoids making another assumption about the origin of clouds and thus is a simple but natural interpretation of Lyα forests at z >= 3 when structures were not yet formed in general. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10. 1086/172380 Bibcode: 1993ApJ. . . 405. . 479B Keywords: Absorption Spectra; Dark Matter; Density (Mass/Volume) ; Hydrogen; Intergalactic Media; Lyman Alpha Radiation; Astronomical Models; Clumps; Doppler Effect; Simulation; Statistical Correlation; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: DARK MATTER; GALAXIES: QUASARS: ABSORPTION LINES; GALAXIES: INTERGALACTIC MEDIUM full text sources ADS | data products SIMBAD (6)