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Mid-infrared Spectral Indicators of Star Formation and Active Galactic Nucleus Activity in Normal Galaxies

Treyer, Marie and Schiminovich, David and Johnson, Benjamin D. and O'Dowd, Matt and Martin, Christopher D. and Wyder, Ted and Charlot, Stéphane and Heckman, Timothy and Martins, Lucimara and Seibert, Mark and van der Hulst, J. M. (2010) Mid-infrared Spectral Indicators of Star Formation and Active Galactic Nucleus Activity in Normal Galaxies. Astrophysical Journal, 719 (2). pp. 1191-1211. ISSN 0004-637X.

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We investigate the use of mid-infrared (MIR) polycyclic aromatic hydrocarbon (PAH) bands, the continuum, and emission lines as probes of star formation (SF) and active galactic nucleus (AGN) activity in a sample of 100 "normal" and local (z ~ 0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer Space Telescope Infrared Spectrograph as part of the Spitzer-SDSS-GALEX Spectroscopic Survey, which includes multi-wavelength photometry from the ultraviolet to the far-infrared and optical spectroscopy. The continuum and features were extracted using PAHFIT, a decomposition code which we find to yield PAH equivalent widths (EWs) up to ~30 times larger than the commonly used spline methods. Despite the lack of extreme objects in our sample (such as strong AGNs, low-metallicity galaxies, or ULIRGs), we find significant variations in PAH, continuum, and emission-line properties, and systematic trends between these MIR properties and optically derived physical properties, such as age, metallicity, and radiation field hardness. We revisit the diagnostic diagram relating PAH EWs and [Ne II]12.8 μm/[O IV]25.9 μm line ratios and find it to be in much better agreement with the standard optical SF/AGN classification than when spline decompositions are used, while also potentially revealing obscured AGNs. The luminosity of individual PAH components, of the continuum, and, with poorer statistics, of the neon emission lines and molecular hydrogen lines are found to be tightly correlated to the total infrared (TIR) luminosity, making individual MIR components good gauges of the total dust emission in SF galaxies. Like the TIR luminosity, these individual components can be used to estimate dust attenuation in the UV and in Hα lines based on energy balance arguments. We also propose average scaling relations between these components and dust-corrected, Hα-derived SF rates.

Item Type:Article
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Martin, Christopher D.0000-0002-8650-1644
Seibert, Mark0000-0002-1143-5515
Additional Information:© 2010 American Astronomical Society. Received 2010 February 17; accepted 2010 June 17; published 2010 July 27.
Subject Keywords:galaxies: active; galaxies: ISM; galaxies: star formation; infrared: galaxies; surveys
Issue or Number:2
Classification Code:PACS: 98.54.Cm; 98.62.Qz; 95.30.Ky; 98.58.Bz; 98.62.Ai; 98.58.Ca
Record Number:CaltechAUTHORS:20100831-152142362
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Official Citation:Marie Treyer et al 2010 ApJ 719 1191 doi: 10.1088/0004-637X/719/2/1191
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19749
Deposited By: Jason Perez
Deposited On:03 Sep 2010 17:52
Last Modified:09 Mar 2020 23:27

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