HI spectra and column densities toward HVC and IVC probes

被引:55
作者
Wakker, BP
Kalberla, PMW
van Woerden, H
de Boer, KS
Putman, ME
机构
[1] Univ Wisconsin, Dept Astron, Madison, WI 53706 USA
[2] Univ Bonn, Inst Radioastron, D-53121 Bonn, Germany
[3] Rijks Univ Groningen, NL-9700 AV Groningen, Netherlands
[4] Sternwarte Univ Bonn, D-53121 Bonn, Germany
[5] Australian Natl Univ, Res Sch Astron & Astrophys, Canberra, ACT, Australia
关键词
Galaxy : halo; ISM : clouds; radio lines : ISM;
D O I
10.1086/321784
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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 of). 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-Ly alpha)/N(H I -9') ranges from 0.74 to 0.98.
引用
收藏
页码:537 / 578
页数:42
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