All Figures

Figure 1: The spectral energy distribution of various ionizing sources (see Sect. 3) as a function of photon energy. Panel  a): silver long-dashed line: spectral energy distribution corresponding to an AGN power-law; short dashed-line: diffuse MBR energy distribution from FGS at comprising only quasars (Q) as sources; continuous line: (original) MBR energy distribution from FGS at comprising both quasar and stellar sources (Q+); dotted line: same as solid line except that the flux beyond 54.4 eV has been reduced by a factor two. Panel  b): continuous line: SED of a zero-age metal-free star of effective temperature 80 000 K; dotted-line: SED of a zero-age metal-free star of effective temperature 88 000 K; long-dashed line: SED from an evolutionary model of CMK04 corresponding to an age of 3.4 Myr and metallicity of 20% solar. Values of are given between brackets for each SED (Sect. 3.1).

Open with DEXTER


In the text

Figure 2: The column ratio derived from photoionization by a power law of index -1.0, as a function of the ionization parameter U. Each model sequence (thin lines) along which U varies represents a slab of fixed column (shown between brackets). Thin black lines connect models of constant column , while thin gray lines connect models of constant column . The gas metallicity is shown using labels, in units of . The thick horizontal broken lines represent four measurements of : the extended absorbers in the high-zradio galaxies 0943-242 (in gray) and 0200+015 (in black) and the two absorbers found in the lensed Lynx arc nebula [ LAN] (in black) and labelled a1 and a2 by Fosbury et al. (2003). The ratios for 0200+015 and a1 are very similar and have been combined into a single entry. The object's name and the column appear to the left and right, respectively, of the corresponding horizontal broken line.

Open with DEXTER


In the text

Figure 3: The column ratio derived from photoionization by the diffuse MBR due to quasars alone, as a function of U. The continuous black line and the long-dashed black line correspond to the thin absorber case assuming metallicities of 0.1 solar and solar, respectively, while the dotted gray line corresponds to the thick absorber case assuming metallicities of 0.01 solar. The nomenclature and symbols have the same meaning as in Fig. 2. In all figures, black line models only apply to the thin absorber objects shown at the top, while gray-line models only apply to 0943-242 below.

Open with DEXTER


In the text

Figure 4: The column ratio derived from photoionization by the MBR due to stars and quasars, as a function of U. The black short-dashed line corresponds to photoionization by the original FGS SED in which the MBR flux is generated by quasars, as well as stars, assuming a gas metallicity of 0.10 . The black short-long dashed line has an SED similar to the previous one, but its flux beyond 54 eV has been halved (thedotted-line SED in Fig. 1a), owing to a larger contribution by stars. The gray dot-dashed line and gray dotted line assume this latter SED inthe thick slab case, but with metallicities of 0.1 and 0.01 , respectively. The nomenclature and symbols have the same meaning as in Fig. 2.

Open with DEXTER


In the text

	Figure 5: The column ratio derived from photoionization by a metal-free stellar atmosphere with  = 80 000 K as described in Sect. 3.4, as a function of U. The nomenclature and symbols have the same meaning as in Fig. 2.
Open with DEXTER


In the text

Figure 6: The column ratio derived from photoionization by stellar energy distributions of varying , as a function of U. In all models, the metallicity is 0.1  and the slab opacity 1014.8  . A label shows the under consideration. The dotted line labelled VM04 corresponds to photoionization by a stellar cluster of metallicity 20% solar and 3.4 Myr of age, as described in Sect. 3.4. The nomenclature and symbols have the same meaning as in Fig. 2.

Open with DEXTER


In the text

	Figure 7: The column ratio derived from photoionization by four different SED s discussed in Sect. 4, as a function of U. The nomenclature and symbols have the same meaning as in Fig. 2.
Open with DEXTER


In the text

	Figure 8: The column ratio derived from photoionization by four different SED s discussed in Sect. 4, as a function of U.
Open with DEXTER


In the text

	Figure 9: The column ratio derived from photoionization by four different SED s discussed in Sect. 4, as a function of U.
Open with DEXTER


In the text

	Figure 10: The column ratio derived from photoionization by four different SED s discussed in Sect. 4, as a function of U.
Open with DEXTER


In the text