Centaurus A - New Clouds on the Horizon

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Centaurus A is a lenticular (intermediate between spiral and elliptical) galaxy, which exhibits a complex variety of dust, gas and stellar regions. The Herschel image reveals thermal emissions emanating from the dusty central band, which was first seen visibly from the Paramatta observatory in Australia in 1826 by James Dunlop, and then famously by Sir John Herschel in 1847 during his work surveying the southern hemisphere skies for the seminal “Outlines of Astronomy”.

Ignored largely for the next century, due in part to a lack of a large observatory in the Southern hemisphere, it was 1954 when astronomers at Mt Palomar first proposed the theory that its unusual appearance was the result of a collision between two galaxies. The unusually large amounts of dust for a galaxy of this type are indicative of a merger between a large elliptical galaxy with a late type spiral galaxy, rich in both dust and gas

As one of the nearest strong radio galaxies to our own, at a distance of around 12 million light years, it is visible in even modest amateur optical equipment, with the dark band of dust clearly bisecting the main elliptical glow.

Herschel’s Spectral and Photometric Imaging Receiver (SPIRE) instrument imaged around 1 degree square of sky over a period of 65 minutes, with Centaurus A occupying the central 15 arcminutes (about the same as the radius of our Moon). This image shows not only Centaurus A with its jets and lobes, but also numerous background galaxies, which appear as point like sources around a slightly “burnt out” core region in Centaurus A.

Both of the jets, the upper left of which in the image measures approximately 15,000 light years, are clearly seen in the Herschel image. Thought to be powered by a supermassive black hole, these jets vanish in visible wavelengths and are most likely mainly due to synchrotron emission from relativistic electrons spiralling around magnetic field lines in the jets.

The observations also reveal for the first time two new clouds at the SPIRE wavelengths which are co-aligned with the jets, at distances of around 50,000 light years from the centre of the galaxy, and are visible only due to Herschel’s extreme sensitivity to emissions from the cold dust at temperatures not far above absolute zero.

This far infrared image, taken as part of the Herschel VNGS (Very Nearby Galaxies Survey) shows the galaxy with unprecedented spatial resolution at these wavelengths, and is key to understanding the physical processes and properties of gas and dust in galaxies.

Credit: ESA/Herschel /SPIRE/C.D Wilson, MacMaster University, Hamilton, Ontario, Canada

Information

  • Observation object: Centaurus A and numerous background galaxies in this wide field image
  • Type: Galaxies
  • Instrument: Spectral and Photometric Imaging Receiver (SPIRE)
  • Observation date: 2012/02/01
  • Right ascension: 13h 25m 28s
  • Declination: -43° 1′ 9″
  • Wavelength: 250-500 um
  • Width: 654 px
  • Height: 692 px
  • Upload date: 2012/02/01 – 11:18

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