Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/~astro/highlights/GALFA/galfa_fvw.pdf Дата изменения: Wed Dec 21 01:58:42 2005 Дата индексирования: Sat Dec 22 13:41:25 2007 Кодировка: Поисковые слова: sun halo

Recent results of Forbidden-Velo city Wings with GALFA
Ji-hyun Kang and Bon-Chul Koo (Seoul National University) Large-scale (,v ) diagrams of Hi 21-cm line emission in the Galactic plane usually show small highveloctiy bumps protruding from their surroundings. Since those wing-like features are at forbidden velocities, i.e., at velocities beyond the maximum or minimum values permitted by the Galactic rotation, we call them as "Forbidden-velocity wings (FVWs)". Fig. 1 (a) is a (,v ) diagram at b = 4 . The wing-like feature at 39 and 80 km s-1 vLSR 130 km s-1 and the one at 83 and 30 km s-1 vLSR 70 km s-1 in Fig. 1 (a) are the examples of FVWs. We suspect that they are the sites where Galactic dynamical events, for example, supernova explosions, stellar winds, or collisions of high-velocity clouds, which could accelerate their surrounding gas, have happended. We have searched for the FVWs using the Leiden-Dwingeloo Hi survey and the Southern Galactic Plane Survey data, and identified about 90 FVWs in the Galactic plane (| b | 13 ) (Kang 2004; Kang et al. 2004). We compared this catalog of FVWs with those of supernova remnants, high-velocity coulds, and nearby galaxies, and found that about 85 % are not coincident with those known ob jects. The natures of most FVWs are not known yet. During last January and Febuarary, for 15 days, we have carried out commensal observations using the ALFA receiver covering areas including 3 FVWs in the inner Galaxy. Two of them showed shell-like features. FVW39.0+4.0 (Fig. 1, b) is an 1 -sized shell of vexp 55 km s-1 . As it goes to higher velocities, it becomes fainter and finally disappears, so that its endcap is not seen. Its systematic velocity seems to be less than 73 km s-1 . Its distance from the Sun would be less than 5.0 kpc or greater than 8.3 kpc. If it is located in the Sagittarius-Carina arm, the kinetic energy of Hi shell would be 1.2 в 1050 erg or 1.0 в 1051 erg, depending on whether it is at close ( 3.3 kpc) or distant ( 9.8 kpc) part of the arm. It doesn't have any known OB type stars inside and could be an old supernova remnant. FVW40.0+0.5 (Fig. 1, c) shows center-filled complex of filamentary structures. Since it shows roughly circular shape, it could possibly be part of an endcap of a larger shell. FVW44.5-2.0 (Fig. 1, d) shows a single clump-like structure from 110 km s-1 to 90 km s-1 , and then connects to a complicated filamentary structure at lower velocities. It seems to be similar to the halo cloud of Lockman (2002) in the sense that it exists near tangent velocity and shows a clump-like structure. These are only three of 26 FVWs observable at Arecibo. Future ALFA survey of the Galactic plane will reveal the nature of FVWs.

REFERENCES Kang, J.-h. 2004, M.Sc. Thesis, Seoul National Univ. Kang, J.-h., Koo, B.-Ch., & Heiles, C. 2004, ASP conference Series, 317, 38 Lockman, F., J. 2002, ApJ, 580, L47 Taylor, J. H., & Cordes, J. M. 1993, ApJ, 411, 674

A This preprint was prepared with the AAS L TEX macros v5.2.


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Fig. 1.-- extended vLSR =73 -114 km

(a) Large-scale (, b) diagram at b = +4 using LD data. Arrow near the center indicates faint bump of FVW39.0+4.0. (b) Arecibo image of FVW39.0+4.0 integrated over velocities between km s-1 and 130 km s-1 . (c) Image of FVW40.0+0.5 integrated from vLSR =-79 km s-1 to s-1 . (c) Image of FVW44.5-2.0 integrated from vLSR =+90 km s-1 to +110 km s-1 .