HI Galactic Halo Cloud G27.0+6.3 (collage)

Minimum credit line: Image courtesy of NRAO/AUI and Yurii Pidopryhora, NRAO & Ohio University(for details, see Image Use Policy).

About this Image

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 (G27.0+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 core and envelope. 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 downward motion. It can be estimated that this cloud is about 7.5 kpc away from us and 850 pc above the Galactic plane. Its size is approximately 20 pc with core size of about 7 pc. This cloud contains 500 solar masses of hydrogen and the density of its core exceeds 20 atoms per cubic cm. The images are false-color with blue corresponding to the least and red -- to the most hydrogen density.

Investigator(s):  Liszt, H., Lockman, J., Rupen, M. (NRAO), Pidopryhora Y. (NRAO & Ohio U)

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Technical Data

    Telescope VLA 
    Date of Observation 2004-07-10 
    Type of Observation Spectral Line Observations 
    Center of Image RA: 18:18:0.00, Dec: -2:15:0.00 (J2000)  
    Field of View 3.0000 x 4.0000 degrees  
    Technical Caption 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. The GBT image is taken from a single channel while the VLA's is imtegrated over all the cloud's linewidth. Cloud's peak column density is 3.5x10^+20 cm^-2 and the line's FWHM is 4.8 km/s, as measured from the VLA data. Distance estimated assuming the cloud resides at the tangent point.  

  • Astronomical database entries for HI cloud G27.0 6.3
    • Query SIMBAD for more HI cloud G27.0 6.3 data


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