A definitive history of Peas should start at the beginning. Almost inevitably, Hanny concocted the Peas thread,
little knowing that one day her humourous point-of-departure would lead to a paper on a group of galaxies
that became identified because they appeared green. But really, Galaxy Zoo and its forum is the parent of
this study; only through so many people looking at so many galaxies and then being able to communicate
their findings has this exciting set of discoveries been produced. Having intelligent and communicative young
astronomers on hand to grasp what opportunities have arisen was always going to produce new science,
which is presumably what this is all about...
Indeed, one of the first peas, a QSO, became noticeable because of its very large redshift z=4.2. But, distance
was not to become what was interesting about Peas. Doubly-ionised oxygen or OIII is the substance that has
set these objects apart, and its proliferation in some of these compact galaxies.
For my own part, I remember this thread being the start of the journey for me.
Posted by Nightwatch, Dec. 10. What Is This Green Colored Thingy?
http://www.galaxyzooforum.org/index.php?topic=8926In this, the OIII part of the spectrum is identified and Zookeeper Kevin gets involved. Fluffy Porcupine correctly
identified what 'OIII' is and where it should be. I had googled 'green star' and come up with a ref that suggests
ionised oxyen is green. For what ever reason, I decided to list as many of these green OIII objects as I could
find, and so built a list of what was initially around 50 objects. Most seemed to be around redshift 0.2 or 3,
and the fact that they were heavy in the r-band (as in RGB) accounted for their greeness. From there, others
started building lists, most notably Starry Night, who became interested in any objects that had this vast OIII
spike- whatever colour. Indeed, he found some very odd-coloured objects including 'grapes'- purple in hue,
through data-mining the entire forum! This was still all 'by hand' though...
It was Starry who initially suggested using coding to get suitable OIII objects. Using SQL to search the SDSS
database is not something that would have occured to me and no-one else seems to have latched on to
that as a method of finding Peas- perhaps then it was still not been taken seriously. By mid-February, lots
of different coloured Peas had been found. Lists were abundant, including many examples from Galaxy
Hunters Inc. Fermat's Brother then became involved and introduced a more rigorous scientific examination
of the spectra and its meanings. Reply #817 seems to encapsulate this more detailed spectral analysis.
By March, 92 greens had been found, but no-one had yet automated the search. Elisabeth from Belgium
was beginning her handiwork and then, FB came up with a SQL program! Amazing! (Reply #885). Then came
along laihro and his positive emitters list of 7000-odd objects. The process was no longer so open-ended;
there seemed to be a reasonably distinct number of these things and by the right programming and knowing
which parametres to use we could isolate them.
Laihro's lists have proved invaluable in sorting the current number of 200+ green ones. Together with
Waveney's merger program, people were able to classify this big list of thousands and condense it into this
grouping Carrie is now writing a paper about. Awesome really; the power of citizen science.
