All Figures

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f1.eps}\par\vspace*{3mm} \includegraphics[width=8.8cm,clip]{H4512f2.eps}\end{figure}$ Figure 1: SDSS spectrum ( $R \simeq 2000$ ) of SDSS J0011+0055. Top: the full spectrum. $F_{\lambda }$ is in units of 10^-17 ergs cm^-2 s^-1 Å^-1. Bottom: a portion of the spectrum illustrating the Si IV $\lambda \lambda$ 1393.75, 1402.77 and C IV $\lambda \lambda$ 1548.20, 1550.78 doublets. Absorption lines at z = 2.29071 (part of system A) and at z = 2.05844 (part of system B) are indicated.
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In the text

$\begin{figure} \par\includegraphics[width=17.55cm,clip]{H4512f3.eps}\par\vspace*{3mm} \includegraphics[width=17.55cm,clip]{H4512f4.eps}\end{figure}$ Figure 2: Portions of the UVES spectrum of SDSS J0011+0055 illustrating the absorption line systems A and B defined in Table 1. System B is best seen in C IV and system A in Si IV (C IV at $z \simeq$ 2.29 is outside the observed UVES spectral range). The following transitions are indicated: N V $\lambda \lambda$ 1238.82, 1242.80, C IV $\lambda \lambda$ 1548.20, 1550.78, Si IV $\lambda \lambda$ 1393.75, 1402.77, Mg II $\lambda \lambda$ 2796.35, 2803.53, Si II $\lambda \lambda$ 1260.42, 1264.74, 1265.00, C II $\lambda \lambda$ 1334.53, 1335.66, 1335.71, and Ly $\alpha$ $\lambda$ 1215.67. For clarity, the two reddest and very close transitions of Si II and C II are represented by single marks at the mean wavelengths; all four of those transitions are excited-state transitions. Absorption from the high-velocity system B is not detected in Si II or C II, and therefore is not plotted although it lies well within the observed UVES spectral range (Si II $\lambda$ 1260.42 could be present in system B1 but the detection is not convincing). Narrow intervening Mg II $\lambda \lambda$ 2796.35, 2803.53 absorption contaminates the Si II absorption of system A2. Narrow intervening C IV $\lambda$ 1548.20 lines are seen slightly longward of the Si IV absorption from system B, along with a broader instrumental artifact. All spectra are plotted on a velocity scale of v/c = (R²-1)/(R²+1) where $R = (1+z_{\rm sys})\: \lambda_{0} / \lambda_{\rm obs}$ , $\lambda _{\rm obs}$ being the observed wavelength, $\lambda _{0}$ the laboratory vacuum rest wavelength of the red transition of the multiplets, and $z_{\rm sys}$ the systemic redshift of the quasar.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{H4512f5.eps}\par\vspace*{1... ...}\par\vspace*{1.5mm} \includegraphics[width=8.6cm,clip]{H4512f7.eps}\end{figure}$ Figure 3: The covering factor and opacity of resonance doublets seen in the low-velocity absorption system A and computed from Eq. (2). From top to bottom: the normalized residual intensities $I_{\rm b}$ (blue) and $I_{\rm r}$ (red); the normalized residual intensity $I_{\rm b}$ (blue) and the square of the normalized residual intensity $I_{\rm r}^{2}$ (black); the covering factor $C_{\rm v}$ ; the opacity expressed as e $^{-\tau _{\rm v}}$ . Horizontal dashed lines indicates the range [0, 1] over which these quantities have a physical meaning. Unphysical values of $C_{\rm v}$ and e $^{-\tau _{\rm v}}$ have been cut to a maximum of 1.1 and a minimum of -0.1.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f8.eps}\par\vspace*{1.5mm} \includegraphics[width=8.8cm,clip]{H4512f9.eps}\end{figure}$ Figure 4: Same as Fig. 3 but for the high-velocity absorption system B.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f10.eps}\end{figure}$ Figure 5: Part of the spectrum illustrating the C II $\lambda$ 1334.53, C II $^{\star }$ $\lambda$ 1335.70, Si II $\lambda$ 1260.42, and Si II $^{\star }$ $\lambda$ 1264.76 transitions in system A1 (cf. Fig. 2). In order to emphasize these features, the spectra are divided by a local continuum, and smoothed using median filtering on 20 km s^-1 boxes. The vertical marks indicate the velocities predicted for these absorption lines at z = 2.29071 (A1).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f11.eps}\end{figure}$ Figure 6: C II and Si II column density ratios $N(X^{\star }) / N(X)$ as a function of the electron density $n_{\rm e}$ in cm^-3. The Si II curves are labeled with the electron temperature; the C II curves follow the same trend.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f8.eps}\par\vspace*{1.5mm} \includegraphics[width=8.8cm,clip]{H4512f9.eps}\end{figure}$	Figure 4: Same as Fig. 3 but for the high-velocity absorption system B.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{H4512f11.eps}\end{figure}$	Figure 6: C II and Si II column density ratios $N(X^{\star }) / N(X)$ as a function of the electron density $n_{\rm e}$ in cm^-3. The Si II curves are labeled with the electron temperature; the C II curves follow the same trend.
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