ESO’s Very Large Telescope (VLT) has made the first detailed observations of a rare dwarf galaxy recently formed within the giant collisional ring surrounding the elliptical galaxy NGC 5291.
This image from ESO’s Very Large Telescope shows the dwarf galaxy NGC 5291N (center). Image credit: ESO.
The large elliptical galaxy NGC 5291 lies in the constellation Centaurus, roughly 195 million light-years away.
Over 360 million years ago, this galaxy was involved in a violent collision as another galaxy traveling at immense speeds barreled into its core. The crash ejected massive streams of gas into intergalactic space, which later coalesced into a ring formation around the galaxy.
Over time, material in the collisional ring gathered and collapsed into several starburst regions and dwarf galaxies.
One of these dwarf galaxies is NGC 5291N, also known as GALEX J134720.86-302055.70.
Massive galaxies are believed to have formed through the build-up of smaller galaxies in the early years of the Universe. These dwarf galaxies, if they have survived on their own up to the present day, now normally contain many extremely old stars.
Yet NGC 5291N appears to contain no old stars, according to a team of astronomers led by Dr Jeremy Fensch of the Paris Diderot University, France.
Among the debris surrounding NGC 5291 (center) is a rare dwarf galaxy, NGC 5291N (appears as a bright clump towards the right of the image). NGC 5291 is currently interacting with MCG-05-33-005 – or the Seashell Galaxy – the unusual comma-shaped galaxy appearing to leech off NGC 5291’s luminous core. Image credit: ESO.
Detailed observations with VLT’s MUSE spectrograph found that the outer parts of this dwarf galaxy had properties typically associated with the formation of new stars, but what was observed is not predicted by current theoretical models.
Dr Fensch and co-authors suspect that these unusual aspects may be the result of massive collisions of gas in the region.
NGC 5291N doesn’t look like a typical dwarf galaxy, but instead it shares a striking number of similarities with the clumpy structures present within starburst galaxies in the early Universe.
This makes it an important cosmic laboratory for the study of early gas-rich galaxies, which are normally much too distant to be observed in detail.
The results were published online September 30 in the journal Astronomy & Astrophysics (arXiv.org preprint).
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J. Fensch et al. Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N. A&A, published online September 30, 2015; doi: 10.1051/0004-6361/201527141
