2001/02/08 by B. P. Wakker, P. M. W. Kalberla, Hugo van Woerden +3 · 2 citations
Chemistry · Engineering · Physics and Astronomy · #Analytical Chemistry (journal) #Angular resolution (graph drawing) #Astronomical Observations and Instrumentation #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Chemistry #Dispersion (optics) #Galaxy #Geometry #Line (geometry) #Line-of-sight #Optics #Physics #Spectral line #Spectral resolution #Stars #Stellar, planetary, and galactic studies #Telescope #Velocity dispersion #astro-ph
paper · pdf · doi:10.1086/321784
published as Astrophys.J.Suppl. 136 (2001) 537-578 · To appear in the "Astrophysical Journal Supplement"; 45 pages; degraded figures (astro-ph restriction) - ask for good versions
arxiv created 2001/02/08 · openalex publication_date 2001/10/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.