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22-08-2007
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HI Absorption in 3C433

Submitter: George Privon
Description: Neutral hydrogen (HI) can absorb radio waves at a rest wavelength of 21cm. By exploiting this, observations of powerful radio galaxies can be used to locate HI clouds in those galaxies, by their absorbtion of the radiation emitted by powerful radio sources behind them. For my project as a summer student at ASTRON, I used VLA and WSRT data to look for HI absorption in radio galaxies with recent star formation. Often, the absorption is seen coincident with the (optical) host galaxy. However, in this case, no absorption is seen at the location of the host galaxy (red contours in the middle of the plot) - the core is too weak to be used for detecting absorption. In this overlay of VLA data, the HI absorption (blue contours) is actually seen against the southern radio hotspot (green contours are radio continuum emission)! This HI might be due to an extended gas disk associated with the galaxy. Or: 3C433 is located in a cluster, and the HI might be gas associated with the cluster (possibly stripped from another galaxy in the cluster?), instead of the radio source.
Copyright: George Privon
 
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