THE GREEN BANK TELESCOPE H II REGION DISCOVERY SURVEY. III. KINEMATIC DISTANCES

被引:69
作者
Anderson, L. D. [1 ]
Bania, T. M. [2 ]
Balser, Dana S. [3 ]
Rood, Robert T. [4 ]
机构
[1] W Virginia Univ, Dept Phys, Morgantown, WV 26506 USA
[2] Boston Univ, Dept Astron, Inst Astrophys Res, Boston, MA 02215 USA
[3] Natl Radio Astron Observ, Charlottesville, VA 22903 USA
[4] Univ Virginia, Dept Astron, Charlottesville, VA 22903 USA
基金
加拿大自然科学与工程研究理事会; 美国国家科学基金会;
关键词
H II regions; ISM: molecules; radio lines: ISM; stars: formation; GALACTIC PLANE SURVEY; RADIO RECOMBINATION LINES; MILKY-WAY; HII-REGIONS; MOLECULAR CLOUDS; ROTATION CURVE; RING SURVEY; TRIGONOMETRIC PARALLAXES; SOUTHERN-HEMISPHERE; SELF-ABSORPTION;
D O I
10.1088/0004-637X/754/1/62
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Using the H I emission/absorption method, we resolve the kinematic distance ambiguity and derive distances for 149 of 182 (82%) H II regions discovered by the Green Bank Telescope H II Region Discovery Survey (GBT HRDS). The HRDS is an X-band (9 GHz, 3 cm) GBT survey of 448 previously unknown H II regions in radio recombination line and radio continuum emission. Here, we focus on HRDS sources from 67 degrees >= l >= 18 degrees, where kinematic distances are more reliable. The 25 HRDS sources in this zone that have negative recombination line velocities are unambiguously beyond the orbit of the Sun, up to 20 kpc distant. They are the most distant H II regions yet discovered. We find that 61% of HRDS sources are located at the far distance, 31% at the tangent-point distance, and only 7% at the near distance. "Bubble" H II regions are not preferentially located at the near distance (as was assumed previously) but average 10 kpc from the Sun. The HRDS nebulae, when combined with a large sample of H II regions with previously known distances, show evidence of spiral structure in two circular arc segments of mean Galactocentric radii of 4.25 and 6.0 kpc. We perform a thorough uncertainty analysis to analyze the effect of using different rotation curves, streaming motions, and a change to the solar circular rotation speed. The median distance uncertainty for our sample of H II regions is only 0.5 kpc, or 5%. This is significantly less than the median difference between the near and far kinematic distances, 6 kpc. The basic Galactic structure results are unchanged after considering these sources of uncertainty.
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页数:15
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