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Probing the Excitation of Extreme Starbursts: High-Resolution Mid-Infrared Spectroscopy of Blue Compact Dwarfs

Hao, Lei and Wu, Yanling and Charmandaris, V. and Spoon, H. W. W. and Bernard-Salas, J. and Devost, D. and Lebouteiller, V. and Houck, J. R. (2009) Probing the Excitation of Extreme Starbursts: High-Resolution Mid-Infrared Spectroscopy of Blue Compact Dwarfs. Astrophysical Journal, 704 (2). pp. 1159-1173. ISSN 0004-637X.

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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 μm 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 μm/[S III]33.48 μm as a function of [Ne III]15.56 μm/[Ne II]12.81 μm 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]/Hα) versus log([O III]/Hβ) 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 μm/[Ne II]12.81 μm versus [S IV]10.51 μm/[S III]18.71 μm 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 μm emission has been detected in the BCDs of our sample.

Item Type:Article
Related URLs:
URLURL TypeDescription
Charmandaris, V.0000-0002-2688-1956
Spoon, H. W. W.0000-0002-8712-369X
Bernard-Salas, J.0000-0002-8452-8675
Additional Information:© 2009 American Astronomical Society. Received 2009 March 26; accepted 2009 August 31; published 2009 September 30. The authors thank the anonymous referee for useful comments which greatly improved the manuscript. We also thank John Moustakas for kindly providing us the optical data of the SINGS sample. Support for this work was provided by NASA through contract number 1257184 issued by the Jet Propulsion Laboratory, California Institute of Technology underNASA contract 1407. V.C. acknowledges partial support from the EU ToK grant 39965 and FP7-REGPOT 206469.
Funding AgencyGrant Number
European Research Council (ERC)39965
European Research Council (ERC)FP7-REGPOT 206469
Subject Keywords:dust, extinction; galaxies: abundances; galaxies: dwarf; galaxies: starburst; infrared: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20091026-113043058
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Official Citation:Probing the Excitation of Extreme Starbursts: High-Resolution Mid-Infrared Spectroscopy of Blue Compact Dwarfs Lei Hao, Yanling Wu, V. Charmandaris, H. W. W. Spoon, J. Bernard-Salas, D. Devost, V. Lebouteiller, and J. R. Houck 2009 ApJ 704 1159-1173 doi: 10.1088/0004-637X/704/2/1159
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16475
Deposited By: Jason Perez
Deposited On:26 Oct 2009 21:35
Last Modified:04 Nov 2019 22:06

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