Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies

Author Info

Carolin Cardamone, Yale University
Kevin Schawinski, Yale University
Marc Sarzi, University of Hertfordshire
Steven P. Bamford, University of Nottingham
Vardha N. Bennert, University of California - Santa BarbaraFollow
C. M. Urry, Yale University
Chris Lintott, University of Oxford
William C. Keel, University of Alabama - Tuscaloosa
John Parejko, Drexel University
Robert C. Nichol, University of Portsmouth
Daniel Thomas, University of Portsmouth
Dan Andreescu, LinkLab
Phil Murray, Fingerprint Digital Media
M. Jordan Raddick, The John Hopkins University
Anže Slosar, Lawrence Berkeley National Lab
Alex Szalay, The John Hopkins University
Jan VandenBerg, The Johns Hopkins University

Recommended Citation

Published in Monthly Notices of the Royal Astronomical Society, Volume 399, Issue 3, November 1, 2009, pages 1191-1205.

NOTE: At the time of publication, the author Vardha Bennert was not yet affiliated with Cal Poly.

The definitive version is available at https://doi.org/10.1111/j.1365-2966.2009.15383.x.

Abstract

We investigate a class of rapidly growing emission line galaxies, known as ‘Green Peas’, first noted by volunteers in the Galaxy Zoo project because of their peculiar bright green colour and small size, unresolved in Sloan Digital Sky Survey imaging. Their appearance is due to very strong optical emission lines, namely [O iii]λ5007 Å, with an unusually large equivalent width of up to ∼1000 Å. We discuss a well-defined sample of 251 colour-selected objects, most of which are strongly star forming, although there are some active galactic nuclei interlopers including eight newly discovered narrow-line Seyfert 1 galaxies. The star-forming Peas are low-mass galaxies (M∼ 10^8.5–10¹⁰ M_⊙) with high star formation rates (∼10 M_⊙ yr⁻¹), low metallicities (log[O/H]+ 12 ∼ 8.7) and low reddening [E(B−V) ≤ 0.25] and they reside in low-density environments. They have some of the highest specific star formation rates (up to ∼10⁻⁸ yr⁻¹) seen in the local Universe, yielding doubling times for their stellar mass of hundreds of Myr. The few star-forming Peas with Hubble Space Telescope imaging appear to have several clumps of bright star-forming regions and low surface density features that may indicate recent or ongoing mergers. The Peas are similar in size, mass, luminosity and metallicity to luminous blue compact galaxies. They are also similar to high-redshift ultraviolet-luminous galaxies, e.g. Lyman-break galaxies and Lyα emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies. Studying starbursting galaxies as a function of redshift is essential to understanding the build up of stellar mass in the Universe.

Disciplines

Physics

Copyright

2009 The Authors.

Publisher statement

Published by the Royal Astronomical Society.