arXiv subjects

Tae-Sun Kim

Publications and source records attributed to Tae-Sun Kim.

39 records · Page 3Linked to original sources

arXiv2000

The detection of oxygen in the low-density intergalactic medium

The abundances of metals in the intergalactic medium (IGM) can be used to constrain the amount of star formation at high redshift and the spectral shape of the ionizing background radiation. For both purposes it is essential to measure the abundances in regions of low density, away from local sources of metals and ionizing photons. Here we report the first detection of OVI in the low-density IGM at high redshift. We perform a pixel-by-pixel search for OVI absorption in eight high quality quasar spectra spanning the redshift range z = 2.0-4.5. At 2 ~< z ~< 3, we clearly detect OVI in the form of a positive correlation between the HI Ly-alpha optical depth and the optical depth in the corresponding OVI pixel, down to an HI optical depth of 0.1. This is an order of magnitude lower in HI optical depth than the best CIV measurements can probe and constitutes the first clear detection of metals in underdense gas. The non-detection of OVI at z > 3 is consistent with the enhanced photoionization from a hardening of the UV background below z ~ 3 but could also be caused by the high level of contamination from Ly series lines.

astro-ph↗

arXiv1997

The Redshift Evolution of the Lyman Alpha Forest

We have analyzed the properties of low column density Lyman alpha forest clouds (12.8 < log N_HI < 16.0) toward 5 QSOs at different redshifts, using high signal-to-noise data from the HIRES spectrograph on the Keck I 10-m telescope. The results are used to study the evolution of these clouds in the interval 2.1 < z < 3.5. We find: 1) The differential density distribution of forest clouds, f(N_HI), fits an empirical power law with a typical slope of -1.35 to -1.55 for clouds with N_HI < 10^14.3 cm^{-2} and changes extremely slowly with redshift over this N_HI range. 2) The deviation of f(N_HI) from this power-law distribution at higher column densities depends on redshift: for higher redshifts, the departure from a power-law distribution occurs at higher N_HI, which means that higher column density clouds rapidly disappear with decreasing redshift. This may be consistent with an invariant shape for the different column density distributions, but with a shift to a lower column density normalization for systems at different redshifts driven by the overall expansion of the universe. 3) The line widths of the forest clouds increase as redshift decreases. 4) The correlation strength of the forest clouds seems to increase as redshift decreases. We discuss these results in terms of the evolution of the IGM comparing the results to models and analytic descriptions of the evolution of structure in the gas.

astro-ph↗

arXiv1995

The Distribution of Column Densities and b Values in the Lyman-Alpha Forest

We describe the properties of the Ly$α$ forest in the column density range $\nhi \geq 2\times10^{12}$ cm$^{-2}$ based on 1056 lines in the wavelength range 4300--5100Åmeasured in extremely high S/N, $R=36,000$ spectra of four quasars. The column density distribution is well described by a -1.5 power law to $2\times10^{12}$ cm$^{-2}$, below which limit confusion becomes too severe to measure a spectrum of individual clouds. The distribution of $b$ values shows a well-defined lower envelope with a cutoff at $b=20\kms$ corresponding to a cloud temperature of 24,000 K. There is only a very small fraction (less than 1%) of narrow line clouds which cannot be identified with metal-lines. From modeling the Ly$α$ absorption lines as complexes of clouds each with thermal broadening corresponding to $b_c$ we find the $b$ distribution can be understood if there is a mean of 3.25 clouds per absorption line with a spread in velocity centroids characterized by a dispersion of $10.75\kms$.

astro-ph↗