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$\begin{figure} \par\includegraphics[width=16.1cm]{aah4375_fig1a.ps} \end{figure}$ Figure 1: Calibrated $\rm ^{12}CO(1{-}0)$ (black) and $\rm ^{12}CO(2{-}1)$ (grey) spectra for all 47 galaxies. The spectra have been smoothed to a velocity resolution of $10\>{\rm km}~{\rm s}^{-1}$ . For those galaxies which are detected in at least one CO line, the solid horizontal line indicates the spectral window over which the CO line fluxes have been integrated. For comparison, the dashed line in each panel denotes the width of the $21\>{\rm cm}$ line, measured at the 20% level (Col. 7 of Table 1) and centered on the observed galaxy recession velocity. Both central velocity and width of the $21\>{\rm cm}$ line are taken from the LEDA database.
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In the text

$\begin{figure}\par\includegraphics[width=16.9cm]{aah4375_fig1b.ps}\end{figure}$ Figure 1: continued.
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In the text

$\begin{figure}\par\includegraphics[width=17.6cm]{aah4375_fig1c.ps}\end{figure}$ Figure 1: continued.
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In the text

$\begin{figure}\par\includegraphics[width=17cm]{aah4375_fig1d.ps}\end{figure}$ Figure 1: continued.
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In the text

$\begin{figure}\par\includegraphics[width=17cm]{aah4375_fig1e.ps}\end{figure}$ Figure 1: continued.
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In the text

$\begin{figure} \par\resizebox{7cm}{!}{\rotatebox{0}{\includegraphics[clip]{fig2a... ...sizebox{7.5cm}{!}{\rotatebox{0}{\includegraphics[clip]{fig2b.eps}}} \end{figure}$ Figure 2: a) Comparison of observed line intensities for the $\rm ^{12}CO(1{-}0)$ and $\rm ^{12}CO(2{-}1)$ transitions. The good agreement of both line intensities suggests that the CO gas extends over the area covered by the $3\>{\rm mm}$ IRAM beam ( $21^{\prime \prime }$ ). b) FWHM of a Gaussian fit to the (1-0) line (Col. 4 of Table 2), compared to the HI $21\>{\rm cm}$ line width, measured at 50% of the peak intensity (from the LEDA database).
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{fig3a.eps}\par\vspace*{2mm} \includegraphics[width=7.5cm,angle=-90,clip]{fig3b.eps} \end{figure}$ Figure 3: a) Normalized histogram of galaxy distances for the Braine et al. (1993) (dashed line) and our sample (solid line). The distance distributions are very similar. b) Intensity of the $\rm ^{12}CO(1{-}0)$ line as a function of angular diameter for our sample (filled squares) and that of Braine et al. (1993) (open squares). See text for discussion.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{fig4a.eps}\par\vspace*{0.4cm} \includegraphics[width=7.5cm,angle=-90,clip]{fig4b.eps} \end{figure}$ Figure 4: a) $\rm H_2$ mass as a function of far-infrared luminosity (taken from LEDA) for our galaxy sample (filled squares), compared to that of Braine et al. (1993) (open squares). The latest-type spirals follow the same relation established for intermediate- and early-type spirals, and extend it to lower luminosities. For galaxies in our sample without IRAS measurements in LEDA, we have used the SCANPI tool provided by the NASA/IPAC Infrared Science Archive (IRSA) to derive an upper limit to the FIR luminosity. b) Same as a), but $\rm H_2$ mass and far-infrared luminosity normalized to the galaxy surface area.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{fig5.eps} \end{figure}$ Figure 5: $\rm H_2$ mass (top) and $M_{\rm H_2}$ / $M_{\rm HI}$ ratio (bottom) as a function of M_B for our galaxy sample (filled squares), compared to that of Braine et al. (1993) (open squares). Here, the $\rm H_2$ mass has been calculated using both the generic Galactic conversion factor (Eq. (3), left) as well as the luminosity-dependent X of Boselli et al. (2002) (Eq. (4), right).
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{fig6.eps} \end{figure}$ Figure 6: $\rm H_2$ mass (top) and $M_{\rm H_2}$ / $M_{\rm HI}$ ratio (bottom) as a function of Hubble-type (as listed in LEDA) for our galaxy sample (filled squares), compared to that of Braine et al. (1993) (open squares). As in Fig. 5, we calculate the $\rm H_2$ mass using the Galactic value for X (left) as well as the luminosity-dependent X of Boselli et al. (2002) (right).
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In the text

$\begin{figure} \par\resizebox{7.5cm}{!}{\rotatebox{270}{\includegraphics[clip]{fig7.eps}}} \end{figure}$ Figure 7: The $\rm ^{12}CO(1{-}0)$ line intensity as a function of $\mu _I^0$ , the central I-band surface brightness of the galaxy disk (i.e. underneath the nuclear star cluster). Nearly all galaxies detected in CO have $\mu_I^0 < 19\>{\rm mag}$ .
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In the text

$\begin{figure} \par\resizebox{7.5cm}{!}{\rotatebox{270}{\includegraphics[clip]{fig8.eps}}} \end{figure}$ Figure 8: $\rm H_2$ mass as a function of the absolute I-band magnitude of the nuclear star cluster. The CO detection rate appears higher for galaxies with more luminous nuclear clusters.
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In the text

$\begin{figure}\par\includegraphics[width=16.9cm]{aah4375_fig1b.ps}\end{figure}$	Figure 1: continued.
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$\begin{figure} \par\includegraphics[width=7.5cm,clip]{fig3a.eps}\par\vspace*{2mm} \includegraphics[width=7.5cm,angle=-90,clip]{fig3b.eps} \end{figure}$	Figure 3: a) Normalized histogram of galaxy distances for the Braine et al. (1993) (dashed line) and our sample (solid line). The distance distributions are very similar. b) Intensity of the $\rm ^{12}CO(1{-}0)$ line as a function of angular diameter for our sample (filled squares) and that of Braine et al. (1993) (open squares). See text for discussion.
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$\begin{figure} \par\includegraphics[width=15cm,clip]{fig5.eps} \end{figure}$	Figure 5: $\rm H_2$ mass (top) and $M_{\rm H_2}$ / $M_{\rm HI}$ ratio (bottom) as a function of M_B for our galaxy sample (filled squares), compared to that of Braine et al. (1993) (open squares). Here, the $\rm H_2$ mass has been calculated using both the generic Galactic conversion factor (Eq. (3), left) as well as the luminosity-dependent X of Boselli et al. (2002) (Eq. (4), right).
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$\begin{figure} \par\includegraphics[width=15cm,clip]{fig6.eps} \end{figure}$	Figure 6: $\rm H_2$ mass (top) and $M_{\rm H_2}$ / $M_{\rm HI}$ ratio (bottom) as a function of Hubble-type (as listed in LEDA) for our galaxy sample (filled squares), compared to that of Braine et al. (1993) (open squares). As in Fig. 5, we calculate the $\rm H_2$ mass using the Galactic value for X (left) as well as the luminosity-dependent X of Boselli et al. (2002) (right).
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$\begin{figure} \par\resizebox{7.5cm}{!}{\rotatebox{270}{\includegraphics[clip]{fig7.eps}}} \end{figure}$	Figure 7: The $\rm ^{12}CO(1{-}0)$ line intensity as a function of $\mu _I^0$ , the central I-band surface brightness of the galaxy disk (i.e. underneath the nuclear star cluster). Nearly all galaxies detected in CO have $\mu_I^0 < 19\>{\rm mag}$ .
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$\begin{figure} \par\resizebox{7.5cm}{!}{\rotatebox{270}{\includegraphics[clip]{fig8.eps}}} \end{figure}$	Figure 8: $\rm H_2$ mass as a function of the absolute I-band magnitude of the nuclear star cluster. The CO detection rate appears higher for galaxies with more luminous nuclear clusters.
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