Green Peas: A Class of Compact Extremely Star-Forming Galaxies

[EigenState]

Galaxy Zoo Green Peas: Discovery of A Class of Compact Extremely Star-Forming Galaxies


Carolin Cardamone^1,2, Kevin Schawinski^2,3, Marc Sarzi⁴, Steven P. Bamford⁵, Nicola Bennert⁶, C.M. Urry^2,3, Chris Lintott⁷, William C. Keel ⁸, John Parejko⁹, Robert C. Nichol¹⁰, Daniel Thomas¹⁰, Dan Andreescu¹¹, Phil Murray¹², M. Jordan Raddick¹³, Anže Slosar¹⁴, Alex Szalay¹³, Jan VandenBerg¹³


Monthly Notices of the Royal Astronomical Society (Mon. Not. R. Astron. Soc.), in press^§


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 SDSS 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 AGN interlopers including 8 newly discovered Narrow Line Seyfert 1 galaxies. The star-forming Peas are low mass galaxies (M~ 10^8.5 - 10¹⁰ M_סּ) with high star formation rates (~ 10 M_סּyr^-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 Myrs. The few star-forming Peas with HST 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 UV-luminous galaxies, e.g., Lyman-break galaxies and Lyman-a emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies. Studying star-
bursting galaxies as a function of redshift is essential to understanding the build up of stellar mass in the Universe.


1.  Astronomy Department, Yale University 208121, New Haven, CT 06520, U.S.A.
2.  Yale Center for Astronomy and Astrophysics, Departments of Physics and Astronomy, Yale University, New Haven, CT 06520, USA
3.  Department of Physics, Yale University, P.O. Box 208121, New Haven, CT 06520, USA.
4.  Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hat?eld, Herts AL10 9AB, UK.
5.  Centre for Astronomy and Particle Theory, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
6.  Department of Physics, University of California, Santa Barbara, CA 93106, USA.
7.  Department of Physics, University of Oxford, Oxford OX1 3RH, UK.
8.  Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL, 35487, USA.
9.  Department of Physics, Drexel University, Philadelphia, PA 19104, USA.
10.  Institute of Cosmology & Gravitation, University of Portsmouth, Portsmouth, PO1 2EG, UK.
11.  LinkLab, 4506 Graystone Ave., Bronx, NY 10471, USA.
12.  Fingerprint Digital Media, 9 Victoria Close, Newtownards, Co. Down, Northern Ireland, BT23 7GY, UK.
13.  Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA.
14.  Berkeley Center for Cosmological Physics, Lawrence Berkeley National Lab, 1 Cyclotron Road, MS 50-5005, Berkeley, CA 94720, USA

§  "In press" signifies that the manuscript has been formally accepted for publication but has yet to appear in print.


Cross-references:

comments, questions and open discussion