Faint, Large-Scale H alpha Filaments in the Milky Way
L. M. Haffner, R. J. Reynolds, S. L. Tufte;
ApJ, 1998, 501, L83
ABSTRACT:During the initial data reduction of the Wisconsin H alpha Mapper (WHAM) H alpha Sky Survey, we have discovered several very long (~30 deg-80
deg) filaments superposed on the diffuse H alpha background.
These
features have no clear correspondence to the other phases of the interstellar
medium revealed by 21 cm, X-ray, IR, or radio continuum surveys, and they have
no readily identifiable origin or source of ionization.
In this Letter,
the data for two of these faint ( I_{{H} alpha }~0 .5-1.5 R) structures are
presented.
The first is an 80 deg long, 2 deg wide arch that extends nearly
perpendicular to the Galactic plane at l=225^{ deg } and attains a maximum latitude of
+51 deg near l=240^{ deg } before reaching the southern boundary of our
survey map at l=270^{ deg } , b=+42^{ deg } .
The vertical portion of this
feature between b= +10 deg and +25 deg is associated with a single radial
velocity component centered at v_{{LSR}}= +16 km s-1 with a FWHM of 27 km s-1.
A
decrease in the velocity is observed from b= +33 deg through +48 deg as the feature
arches toward higher Galactic longitudes.
At this end, the emission
component is centered near v_{{LSR}}= -20 km s-1.
Where this feature appears to
meet the Galactic plane near l=225^{ deg } , it is directly above the H II
region surrounding CMa R1/OB1.
A second filament consists of a ~25 deg-30 deg
long arc spanning l=210^{ deg } -240 deg at b= +30 deg to +40 deg.
The radial
velocity of this feature increases systematically from 0 km s-1 at l=215^{ deg } ,
b= +38 deg to +18 km s-1 at l=236^{ deg } , b= +28 deg.
Both features have
rather constant intensities along their entire lengths, ranging from 0.5 to
1.5 R (EM = 1-3 cm-6 pc) with no obvious trends.
KEYWORDS: ism: structure, galaxy: structure, galaxy: halo
PERSOKEY:halpha, h+, milky way, optical, ,
CODE: haffner98