MULTIPLE ABSORPTION-LINE SPECTROSCOPY OF THE INTERGALACTIC MEDIUM. I. MODEL

作者：Yao Yangsen^*; Shull J Michael; Danforth Charles W; Keeney Brian A; Stocke John T

来源：Astrophysical Journal, 2011, 730(2): 143.

DOI：10.1088/0004-637X/730/2/143

• cosmology: observations
• intergalactic medium
• quasars: absorption lines
• ultraviolet: general

We present a physically based absorption-line model for the spectroscopic study of the intergalactic medium (IGM). This model adopts results from Cloudy simulations and theoretical calculations by Gnat & Sternberg to examine the resulting observational signatures of the absorbing gas with the following ionization scenarios: collisional ionization equilibrium (CIE), photoionization equilibrium, hybrid (photo-plus collisional ionization), and non-equilibrium cooling. As a demonstration, we apply this model to new observations made with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope of the IGM absorbers at z similar to 0.1877 along the 1ES 1553+113 sight line. We identify Ly alpha, C III, O VI, and N V absorption lines with two distinct velocity components (blue at z(b) = 0.18757; red at z(r) = 0.18772) separated by Delta(cz)/(1 + z) approximate to 38 km s(-1). Joint analyses of these lines indicate that none of the examined ionization scenarios can be applied with confidence to the blue velocity component, although photoionization seems to play a dominant role. For the red component, CIE can be ruled out, but pure photoionization and hybrid scenarios (with T < 1.3 x 10(5) K) are more acceptable. The constrained ranges of hydrogen density and metallicity of the absorbing gas are n(H) = (1.9-2.3) x 10(-5) cm(-3) and Z = (0.43-0.67) Z(circle dot). These constraints indicate O VI and H I ionization fractions, f(OVI) = 0.10-0.15 and f(HI) = (3.2-5.1) x 10(-5), with total hydrogen column density N-H = (0.7-1.2) x 10(18) cm(-2). This demonstration shows that the joint analysis of multiple absorption lines can constrain the ionization state of an absorber, and results used to estimate the baryonic matter contained in the absorber.

• 出版日期2011-4-1