Thursday, May 26, 2011

NGC 5364

The beautiful face on spiral galaxy NGC 5364 is shown above in a false-colour optical image. The extensive spiral arm structure is clearly visible, winding around the central galaxy bulge. The bright coloured spots within the spiral arms indicate the positions of HII regions which are areas of large (some can be several hundred light years across!) clouds of ionized gas associated with intense star formation. The galaxy is located in the Virgo cluster around 70 million light years from Earth (redshift of 0.004) from us.

NGC 5364 was observed using the RSS on SALT in Fabry-Perot mode on 11th May 2011. A succession of 60s images scanning across the H-alpha (6563A) emission line were taken and three of those images were combined to produce the colour picture above. The colours shown provide a sense of the rotation of the spiral arms. Blue colours show regions that are moving towards us (the peak of the line emission is blueshifted relative to its rest wavelength) and red colours show regions that are moving away from us (the emission is redshifted).

Foreground stars are visible in white in the image, and if you look carefully you can spot the Fabry-Perot ghost of the bright star on the bottom left of the image. The ghost is situated at the top right of the image. As a consequence of not auto-guiding during these observations, the position of the ghost is slightly different in each individual image frame used to produce the resultant colour image and therefore the three constituent colours are clearly separated in the final picture.

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