Red Peas
What are Pea galaxies? Pea galaxies are luminous compact galaxies. Red Peas are found between a redshift of .38 and .642 and have an absolute i filter magnitude between -21.23 and -25.39 (the sun has an absolute magnitude of 4.77). The spectra are dominated by a narrow line OIII emission with a narrow Hβ emission and a minimal MgII emission.
Pea galaxies are most likely a type of starburst galaxy – galaxies experiencing a high level of star formation. A starburst can last for tens of millions of years and during that time the galaxy can experience star formation rates tens or hundreds of times greater than in a normal galaxy.
How and when were Peas discovered?
Green Peas were first found and named by amateur astronomers on Galaxy Zoo, a website run by a both professional and amateur astronomers that classifies and sorts SDSS data (see below). They were identified around the summer of 2007 and named peas because they look like peas.
What is the difference between Red and Green Peas?
The obvious difference between the two types of galaxies is the color. The color of the galaxy is determined by the location of the OIII emission. Due to a difference in redshift, the OIII emission line appears in different filters on the telescope, which are assigned different colors.green_pea.jpggreen_pea_spectra.gif


How was data gathered about Pea galaxies?
The data on Pea galaxies was retrieved from the Sloan Digital Sky Survey (SDSS), which releases all of its data in an online database. SDSS began in 2000 as an astronomy survey. It has observed over a quarter of the sky and has catalogued 357 million unique objects with spectroscopic data for more than 1.6 million of those objects. SDSS uses a 2.5 meter telescope located at the Apache Point Observatory in New Mexico. The telescope is equipped with 30 CCDs arranged into six columns with five rows. SDSS uses five filters (one per row) on their CCDs: u, g, r, i, and z. SDSS uses two spectrographs to collect spectroscopic data.telescope_diagram.giftelescope_actual.giffilter_curve.JPG

How do Peas help us understand the universe?
There is still a lot we do not know about starburst galaxies. According to the most popular theory, a starburst is triggered when galaxies interact. Interaction, like a collision, can send shock waves through a galaxy causing gas and dust to collapse and form new stars. The new stars are very massive, use up their fuel quickly, and then die in a supernova which creates more shockwaves. A starburst is the result of this chain reaction sweeping through the galaxy.
Starburst galaxies can help us learn more about how galaxies interactions and galaxy evolution. Since we cannot observe a collision from beginning to end, we must find examples of collisions at every stage in order to study them.

What’s special about it?Red Peas are special because they have not been studied very much. There is one published paper on Green Peas (Cardamone et al., 2009), but no published papers on Red Peas.
Current EventsThis year my science fair project examined Red Peas and compared them to Green Peas. In order to compare them, I calculated the absolute magnitude in different filters for both the Red and Green Peas. The most interesting thing I found was an absence of brighter magnitude Green Peas. This could possibly be explained by the evolution of the rate of star formation in Peas over time.


Personal Views and Questions
I think Red Peas are fascinating because I had never heard of starburst galaxies before. I think they are exciting galaxies to study because there is so much going on in them. This topic doesn’t raise any questions about faith and it didn't change any of my previous views or beliefs. My questions stem from wanting to know more about these galaxies and how they formed. I would like to have more HST images of Pea galaxies because I think they could tell us a lot. I also would like to know more about what the galaxies looked like before the starburst: Were they already compact? Did they have other structure? What other galaxies are nearby?
Cardamone et al., 2009


All images from SDSS unless otherwise noted