Polycyclic Aromatic Hydrocarbons in Galaxies at z ~ 0.1: The Effect of Star Formation and Active Galactic Nuclei

Creators: O'Dowd, Matthew J.; Schiminovich, David; Johnson, Benjamin D.; Treyer, Marie A.; Martin, Christopher D.; Wyder, Ted K.; Charlot, S.; Heckman, Timothy M.; Martins, Lucimara P.; Seibert, Mark; van der Hulst, J. M.

Abstract

We present the analysis of the polycyclic aromatic hydrocarbon (PAH) spectra of a sample of 92 typical starforming galaxies at 0.03 < z < 0.2 observed with the Spitzer intensified Reticon spectrograph (IRS). We compare the relative strengths of PAH emission features with Sloan Digital Sky Survey optical diagnostics to probe the relationship between PAH grain properties and star formation and active galactic nuclei (AGNs) activity. Short-to-long wavelength PAH ratios, and in particular the 7.7 μm-to-11.3 μm feature ratio, are strongly correlated with the star formation diagnostics D_n(4000) and Hα equivalent width, increasing with younger stellar populations. This ratio also shows a significant difference between active and non-active galaxies, with the active galaxies exhibiting weaker 7.7 μm emission. A hard radiation field as measured by [O III]/Hβ and [Ne III]_(15.6μm)/[Ne II]_(12.8μm) effects PAH ratios differently depending on whether this field results from starburst activity or an AGN. Our results are consistent with a picture in which larger PAH molecules grow more efficiently in richer media and in which smaller PAH molecules are preferentially destroyed by the AGN.

Additional Information

© 2009 The American Astronomical Society. Received 2009 March 7; accepted 2009 August 24; published 2009 October 16. We thank the anonymous referee for valuable comments that improved the quality of this work. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. The GALEX is NASA's small explorer. We gratefully acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiale of France and the Korean Ministry of Science and Technology. We thank the MPA/JHU collaboration for SDSS studies for making their catalogs publicly available. This work utilized the PAHFIT IDL tool for decomposing IRS spectra, which J. D. Smith has generously made publicly available (Smith et al. 2007). Funding for the SDSS has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, NASA, NSF, the U.S. Department of Energy, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck- Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. Facilities: Spitzer (IRS), GALEX, SDSS.

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