Context : We present new ^ { 12 } CO ( 1-0 ) observations of 59 late-type galaxies belonging to the Herschel Reference Survey ( HRS ) , a complete K-band-selected , volume-limited ( 15 \lesssim D \lesssim 25 Mpc ) sample of nearby galaxies spanning a wide range in morphological type and luminosity .
We studied different recipes to correct single-beam observations of nearby galaxies of different sizes and inclinations for aperture effects .
This was done by comparing single-beam and multiple-beam observations along the major axis , which were corrected for aperture effects using different empirical or analytical prescriptions , to integrated maps of several nearby galaxies , including edge-on systems observed by different surveys .
The resulting recipe is an analytical function determined by assuming that late-type galaxies are 3D exponentially declining discs with a characteristic scale length r _ { CO } = 0.2 r _ { 24.5 } , where r _ { 24.5 } is the optical , g - ( or B- ) band isophotal radius at the 24.5 mag arcsec ^ { -2 } ( 25 mag arcsec ^ { -2 } ) , as well as a scale height z _ { CO } = 1/100 r _ { 24.5 } .
Our new CO data are then combined with those available in the literature to produce the most updated catalogue of CO observations for the HRS , now including 225 out of the 322 galaxies of the complete sample .
The 3D exponential disc integration is applied to all the galaxies of the sample to measure their total CO fluxes , which are later transformed into molecular gas masses using a constant and a luminosity-dependent X _ { CO } conversion factor .
We also collect H i data for 315 HRS galaxies from the literature and present it in a homogenised form .

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