No abstract

We report an accurate distance of d = 10 ± 2.5 kpc to the high-velocity cloud Complex C. Using high signal-to-noise Keck/HIRES spectra of two horizontal-branch stars, we have detected Ca II K absorption lines from the cloud. Significant non-detections toward a further 3 stars yield robust lower distance limits. The resulting H I mass of Complex C is M H I = 4.9 +2.8 −2.2 × 10 6 M ⊙ ; a total mass of M tot = 8.2 +4.6 −2.6 × 10 6 M ⊙ is implied, after corrections for helium and ionization. At 10 kpc, Complex C has physical dimensions 3 × 15 kpc, and if it is as thick as it is wide, then the average density is log n ≃ −2.5. We estimate the contribution of Complex C to the mass influx may be as high as ∼ 0.14 M ⊙ yr −1 .

We show 21-cm line profiles in the direction of stars and extragalactic objects, lying projected on highand 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. Wakker (2001) (Paper I) 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 fit by one component the distribution of ratios has a larger dispersion. Comparison with higher angular resolution data is possible for sixteen sightlines. Eight sightlines 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 sightlines N(H I-Lyα)/N(H I-9 ′ ) ranges from 0.74 to 0.98.