Strangulation Of Spiral Galaxies: ‘Missing Link’ Discovered

These images of three galaxies from the Galaxy Zoo (top) and STAGES surveys (bottom) show examples of how the newly discovered population of red spiral galaxies on the outskirts of crowded regions in the Universe may be a missing link in our understanding of galaxy evolution. At left, both surveys find examples of normal spiral galaxies displaying all the hallmarks of youth: blue in colour, they are disk-like in structure. The obvious spiral arms host knotty structures where large numbers of hot young stars are being born. On the right are examples of typical rounded balls of stars known as elliptical galaxies. The reddish colour indicates that their stars are mostly old. With no gas left to use as fuel to form any more, they are old, dead and red In the centre are examples of the new "red spiral" galaxy found in large numbers by both the STAGES and Galaxy Zoo collaborations. While still disk-like and recognizably spiral in shape, their spiral arms are smoother. Furthermore, their colour is as red as the ellipticals. Astronomers from both teams believe these red spirals are objects in transition, where star formation has been shut off by interactions with the environment. (Credit: STAGES image credit: Marco Barden, Christian Wolf, Meghan Gray, the STAGES survey; STAGES image from Hubble Space Telescope, colour from COMBO-17 survey; Galaxy Zoo image credit: Sloan Digital Sky Survey)

From Science Daily:

ScienceDaily (Nov. 25, 2008) — Astronomers in two UK-led international collaborations have separately uncovered a type of galaxy that represents a missing link in our understanding of galaxy evolution.

Galaxy Zoo, which uses volunteers from the general public to classify galaxies, and the Space Telescope A901/902 Galaxy Evolution Survey (STAGES) projects have used their vast datasets to disentangle the roles of "nature" and "nurture" in changing galaxies from one variety to another.

Both studies have identified a population of unusual red spiral galaxies that are setting out on the road to retirement after a lifetime of forming stars. Crucially, nature and nurture appear to play a role in this transformation: both the mass of a galaxy as well as its local environment are important in determining when and how quickly its star formation is shut down. The scientists’ work appears together in a forthcoming edition of Monthly Notices of the Royal Astronomical Society.

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