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The Statistical and Physical Properties of the Low Redshift Lyman Alpha Forest Observed with HST/STIS | | Romeel Davé
; Todd M. Tripp
; | | Date: |
23 Dec 2000 | | Journal: | 2001ApJ...553..528D | | Subject: | astro-ph | | Affiliation: | Arizona) and Todd M. Tripp (Princeton | | Abstract: | We examine the Ly-alpha absorber population at z<0.3 detected in spectra of the QSOs PG0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We compare their statistical properties to those in carefully-constructed mock quasar spectra drawn from a cosmological hydrodynamic simulation of a Lambda-CDM universe. We find very good agreement in the column density and b-parameter distributions, down to the smallest observable absorbers with N_HIapprox 10^{12.3} cm^-2. The observed absorber population is complete for N_HIga 10^{13} cm^-2, with a column density distribution slope of eta=2.04pm 0.23 and a median b-parameter of 21 km/s above this limit. The intergalactic gas giving rise to these weak absorbers is analogous to that at high redshift, located in diffuse large-scale structures that are highly photoionized by the metagalactic UV flux, though a greater number arise within shock-heated warm gas. The density, temperature, and column density of these absorbers follow similar relationships to those at high redshift, though with substantially larger scatter due to the shock-heated gas. The b-parameters typically have a significant contribution from thermal broadening, which facilitates a measurement of the low-z IGM temperature as traced by Ly-alpha absorbers. From our simulation we estimate T_IGMsim 5000 K, with an upper limit of 10^4 K, at the mean density. The agreement in predicted and observed amplitude of the column density distributions allows us to measure the HI photoionization rate at z=0.17 to be 10^{-13.3pm 0.7} s^{-1} (estimated modeling uncertainty), close to predictions based on quasar properties. | | Source: | arXiv, astro-ph/0101419 | | Services: | Forum | Review | PDF | Favorites | |
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