Optical Emission from High Velocity Clouds and the Nature of HVCs

Details Optical Emission from High Velocity Clouds and the Nature of HVCs Optical Emission from High Velocity Clouds and the Nature of HVCs

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.9703w&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #97.03; Bulletin of the American Astronomical Society, Vol. 31, p.1516

Other

2

Scientific paper

The nature and origin of the high-velocity clouds of neutral hydrogen remain controversial, and the distances of most HVCs are poorly constrained. Only the large northern HVC complexes M and A have upper distance limits, of <5 and 4--10 kpc, from absorption against halo stars (Danly et al 1993, van Woerden et al 1999). These HVCs have diffuse H-alpha emission of 80--200 milli-Rayleighs (mR) (Tufte, Reynolds & Haffner 1998). We report results from a search of 20 high velocity clouds for faint diffuse optical emission lines in H-alpha and [N II], using a Fabry-Perot at the Las Campanas 2.5-m telescope. A few small complexes are ``bright,'' with H-alpha emission from 100--400 mR and high [N II]/H-alpha. Many HVCs are very faint in H-alpha: HVCs from the Anticenter, Galactic Center Negative, and Extreme Positive complexes have H-alpha from <15 to 30 mR. We construct a simple model for the ionizing flux emergent from the galaxy, normalized by the northern ``bright'' HVCs with known distances and H-alpha fluxes. If the H-alpha from HVCs is produced by ionizing flux escaping from the Galaxy, the H-alpha flux can be used to infer distances for HVCs. The model places the very faint HVCs at distances of 20--60 kpc, in the outer Galactic halo. If H-alpha can be produced by other mechanisms, than these distances could be lower limits. Independent of the model or mechanism, the HVCs that are very faint in H-alpha should be much farther away than the nearby ``bright'' HVCs. The faint HVCs are too far away to be produced by a Galactic fountain, and represent a significant amount of gas accreting onto the Galaxy. This work has been supported by a Carnegie Barbara McClintock Fellowship.

Affiliated with

Also associated with

No associations

Rating

Optical Emission from High Velocity Clouds and the Nature of HVCs does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Optical Emission from High Velocity Clouds and the Nature of HVCs, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical Emission from High Velocity Clouds and the Nature of HVCs will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1746379