Milky Way

Emission Line Maps of the Milky Way

On August 8, 1996, WHAM obtained its first test map from the Galaxy during final testing at Pine Bluff Observatory in Wisconsin. Shortly after, it was moved to Kitt Peak and began it's primary task: mapping the entire sky in Hα. Most of the data for the northern sky was obtained during 1997 and 1998 while the southern sky was observed in 2009 and 2010. After Hα was well in hand, we began mapping select portions of the sky in other emission lines, including [S II] 6717Å, [N II] 6583Å, and Hβ (see Emission Line Studies). Some multi-wavelength maps of interesting regions of the sky have been published (see our publications list for several selections). The Hα survey is available in the Survey section of this site.

WHAM's velocity-resolved maps nicely complement the narrow-band filter imaging projects such as the Virginia Tech Spectral Line Sky Survey and the Southern Hα Sky Survey Atlas (SHASSA).

Intermediate- and High-velocity Clouds

Emission-line studies of HVCs provide many new clues about the nature of these elusive objects. Until recently, HVCs and IVCs were studied almost exclusively through maps of the 21 cm line of neutral hydrogen and a handful of absorption line studies toward more distant objects. We can tune WHAM's velocity window to observe gas outside the ±100 km/s window about the local standard of rest covered by the sky survey. We have made many observations toward known neutral and highly-ionized HVCs, finding ionized gas in nearly all those observed to date. Hα and [S II] 6716Å from several of these regions have been published (see Papers for details). Hα emission from intermediate-velocity gas often appears in the primary survey, which is also highlighted in a few of our publications.

H II Regions

Aside from being interesting studies in their own right, H II regions can be used as probes for the ionizing radiation of their parent star(s). Since interstellar hydrogen is particularly efficient at attenuating radiation shortward of 912Å, direct observations of the far-ultraviolet radiation from hot stars is rare. WHAM fills an interesting niche here by detecting faint H II regions around isolated main sequence and evolved O and B stars (e.g., Reynolds et al. 2005). Since we can also map these regions in other emission lines, these new finds may be good constraints for those trying to model the spectrum of hot stars.


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