Arp Peculiar Galaxies - Indexed 4 entries

 
 
Peculiar galaxies are those that do not fit a conventional galaxy classification scheme, such as the Hubble tuning fork. Peculiar galaxies represent the “outer limits” of what is known about the processes and dynamics that shape galaxies. What makes them so challenging to interpret also makes them compelling to behold.
Since Hubble’s day, astronomers have classified galaxies according to their appearance at visual wavelengths. However, the advent of radio, ultraviolet, and near-infrared observations have shown that a galaxy’s appearance can substantially morph with wavelength. A normal spiral can appear distinctly abnormal depending on whether it is seen in ultraviolet or near-infrared light. Dust as well as its core energy output can also affect a galaxy’s appearance at wavelengths other than in the visual band.
A further development occurred around 1995 and 1996 when the Hubble Deep Fields North and South brought to light thousands of previously unknown fragmented and distorted galaxies extending out to the edge of the visible Universe, each within a parcel of sky no larger than a pin point.
Halton Arp catalogued an Atlas of Peculiar Galaxies through a photographic investigation of these curiosities in 1962 at time when galactic morphologists were attempting to describe evolutionary trends by systematically sorting galaxies by shape. This was first represented by the classic “tuning fork” diagram devised by Edwin Hubble thirty years earlier. Knut Lundmark also introduced an index to indicate how concentrated the light was at the centre of anagalactic nebulae. However, the kind of galaxies that Arp turned up could not simply be pronged onto a tine of the Hubble tuning fork or dropped into one of Lundmark’s bins.
One of the first serious attempts at including peculiar type galaxies in a classification system came in 1958 when the French-American astronomer Gerard de Vancouleurs and Allan Sandage developed an ambitious three-dimensional classification scheme to accommodate as many galaxy shapes as possible. Notwithstanding all the attempts at galaxy classification, the problem remained that nobody knew what forces shaped normal galaxies, much less peculiar ones.
The overall aim of this project is to present a number of examples of various kinds of peculiar galaxies visible in the Southern sky. It will form part of a larger project to photograph 100 of these galaxies as part of an Astronomical League challenge over the course of many months, if not years.
I am fortunate in that many peculiar galaxies are visible in my skies at the present time. The majority of the 338 fall in the 12th to 18th magnitude range; however, there are over 100 Arp objects below magnitude 13.5.

IC342

[1] Arp 82, NGC 2535/6
2009, Mar 15

NGC891


[2] Arp 85, M51
2009, Mar 14

M83

[3] Arp 153, Centaurus A
2009, May 1

M101

[4] Arp 244, NGC 4038/4039
2009, Mar 15


 

 
 
 
 
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