HI Galactic Halo Cloud G19.4+6.3 (collage)



Since 2002 hundreds of HI (neutral hydrogen) clouds have been discovered with the help of the new unique NRAO instrument -- 100 m Green Bank Telescope (GBT). These clouds are a completely new class of objects presenting a previously unknown phenomenon of the interstellar matter physics. Several brightest of them have been observed with another NRAO instrument, Very Large Array (VLA) which provides better angular resolution. This collage shows one of such clouds (G19.4+6.3) as seen at its peak by the GBT in the larger Galactic halo context and its VLA HI column density map with two VLA sample spectra taken at the cloud's cores. The GBT image shows that the cloud is a part of a larger cloud-filament structure, while the VLA image reveals that the cloud has a "dense core - diffuse envelope" structure. The assymetry of the envelope might also suggest a sideway motion. It can be estimated that this cloud is about 8 kpc away from us and 900 pc above the Galactic plane. Its size is approximately 30 pc with core size of about 10 pc. This cloud contains 800 solar masses of hydrogen and the desity of its cores exceeds 20 atoms per cubic cm. The images are false-color with blue corresponding to the least and red -- to the most hydrogen density.
The resolutions: GBT image -- 9 arcmin, VLA (taken in D-array) -- 1 arcmin. GBT exposure 5 sec per 3 by 3 arcmin pixel, VLA -- a few hours. Cloud's peak column density is 4x10^+20 cm^-2 and the line's FWHM is 4.4 km/s, as measured from the VLA data.


Legacy Astronomical Images


NRAO/AUI/NSF does not hold full copyright for this image. Contact the archivist for details.


Legacy Astronomical Image

Object Name

HI cloud G19.4+6.3

Photo Credit

Yurii Pidopryhora, NRAO & Ohio University


H. Liszt, J. Lockman, M. Rupen, Y. Pidopryhora


Very Large Array (VLA)
Green Bank Telescope (GBT)

Observation Date


Type of Observation

spectral line

Center of Image

RA 18:4:0.000, Dec: -8:58:0.000 (J2000)

Field of View

2.000000 x 6.000000 degrees


Contact the archivist for a high resolution tif of this image.


Galactic Sources Series


Galactic Halo Unit


Legacy Astronomical Images, “HI Galactic Halo Cloud G19.4+6.3 (collage),” NRAO Archives, accessed December 3, 2021, https://www.nrao.edu/archives/items/show/33448.