H I spectra and column densities toward HVC and IVC probes

We show 21 cm line profiles in the direction of stars and extragalactic objects, lying projected on high-and intermediate-velocity clouds (HVCs and IVCs). About half of these are from new data obtained with the Effelsberg 100 m telescope, about a quarter are extracted from the Leiden-Dwingeloo Survey (LDS), and the remaining quarter were observed with other single-dish telescopes. H I column densities were determined for each HVC/IVC. Paper I of this series uses these in combination with optical and ultraviolet high-resolution measurements to derive abundances. Here an analysis is given of the difference and ratio of N(H I) as observed with a 9′ versus a 35′ beam. For HVCs and IVCs the ratio N(H I-9′)/ N(H I-35′) lies in the range 0.2-2.5. For low-velocity gas this ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85-1.4, but it appears that the correction for stray radiation is slightly off). The smaller range for the low-velocity gas may be caused by confusion in the line of sight, so that a low ratio in one component can be compensated by a high ratio in another-for 11 low-velocity clouds fitted by one component the distribution of ratios has a larger dispersion. Comparison with higher angular resolution data is possible for 16 sight lines. Eight sight lines with H i data at 1′-2′ resolution show a range of 0.75-1.25 for N(H I-2′)/N(H I-9′), while in eight other sight lines N(H I-Lyα)/N(H I-9′) ranges from 0.74 to 0.98.