PROBING THE EXCITATION OF EXTREME STARBURSTS: HIGH-RESOLUTION MID-INFRARED SPECTROSCOPY OF BLUE COMPACT DWARFS

Journal Article · Tue Oct 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/704/2/1159· OSTI ID:21367369

Lei, Hao ^[1]; Yanling, Wu ^[2]; Charmandaris, V ^[3]; Spoon, H W. W.; Bernard-Salas, J; Lebouteiller, V; Houck, J R ^[4]; Devost, D ^[5]

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1. University of Texas at Austin, McDonald Observatory, 1 University Station, C1402, Austin, TX 78712-0259 (United States)
2. Caltech, Infrared Processing and Analysis Center, MC 314-6, Pasadena, CA 91125 (United States)
3. University of Crete, Department of Physics, P.O. Box 2208, GR-71003, Heraklion (Greece)
4. Cornell University, Astronomy Department, Ithaca, NY 14853-6801 (United States)
5. CFHT: Canada France Hawaii Telescope, Kamuela, HI, 96743 (United States)

We present an analysis of the mid-infrared emission lines for a sample of 12 low-metallicity blue compact dwarf (BCD) galaxies based on high-resolution observations obtained with Infrared Spectrograph on board the Spitzer Space Telescope. We compare our sample with a local sample of typical starburst galaxies and active galactic nuclei (AGNs) to study the ionization field of starbursts over a broad range of physical parameters and examine its difference from the one produced by the AGN. The high-ionization line [O IV]25.89 mum is detected in most of the BCDs, starbursts, and AGNs in our sample. We propose a diagnostic diagram of the line ratios [O IV]25.89 mum/[S III]33.48 mum as a function of [Ne III]15.56 mum/[Ne II]12.81 mum which can be useful in identifying the principal excitation mechanism in a galaxy. Galaxies in this diagram split naturally into two branches. Classic AGNs as well as starburst galaxies with an AGN component populate the upper branch, with stronger AGNs displaying higher [Ne III]/[Ne II] ratios. BCDs and pure starbursts are located in the lower branch. We find that overall the placement of galaxies on this diagram correlates well with their corresponding locations in the log([N II]/Halpha) versus log([O III]/Hbeta) diagnostic diagram, which has been widely used in the optical. The two diagrams provide consistent classifications of the excitation mechanism in a galaxy. On the other hand, the diagram of [Ne III]15.56 mum/[Ne II]12.81 mum versus [S IV]10.51 mum/[S III]18.71 mum is not as efficient in separating AGNs from BCDs and pure starbursts. Our analysis demonstrates that BCDs in general do display higher [Ne III]/[Ne II] and [S IV]/[S III] line ratios than starbursts, with some reaching values even higher than those found at the centers of AGNs. Despite their hard radiation field though, no [Ne V]14.32 mum emission has been detected in the BCDs of our sample.

• OSTI ID: 21367369
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 704; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTROSCOPY
ABUNDANCE
CLASSIFICATION
DUSTS
ENERGY-LEVEL TRANSITIONS
EXCITATION
GALAXIES
GALAXY NUCLEI
INFRARED SPECTRA
IONIZATION
SPECTRA
SPECTROSCOPY
TELESCOPES