MID-INFRARED SPECTRAL INDICATORS OF STAR FORMATION AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN NORMAL GALAXIES

Journal Article · Fri Aug 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/719/2/1191· OSTI ID:21457102

Treyer, Marie; Martin, Christopher D; Wyder, Ted ^[1]; Schiminovich, David; O'Dowd, Matt ^[2]; Johnson, Benjamin D ^[3]; Charlot, Stephane ^[4]; Heckman, Timothy ^[5]; Martins, Lucimara ^[6]; Seibert, Mark ^[7]

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1. California Institute of Technology, MC 278-17, 1200 E. California Boulevard, Pasadena, CA 91125 (United States)
2. Astronomy Department, Columbia University, 550 W. 120 St., New York, NY 10027 (United States)
3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
4. Institut d'Astrophysique de Paris, UMR 7095, 98bis Bvd Arago, 75014 Paris (France)
5. Department of Physics and Astronomy, Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)
6. NAT-Universidade Cruzeiro do Sul, Rua Galvao Bueno, 868, Sao Paulo, SP, 01506-000 (Brazil)
7. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

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 {approx} 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 {approx}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 {mu}m/[O IV]25.9 {mu}m 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 H{alpha} lines based on energy balance arguments. We also propose average scaling relations between these components and dust-corrected, H{alpha}-derived SF rates.

• OSTI ID: 21457102
• Journal Information: Astrophysical Journal, Vol. 719, Issue 2; Other Information: DOI: 10.1088/0004-637X/719/2/1191; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
DUSTS
EMISSION
ENERGY BALANCE
GALAXIES
LUMINOSITY
NEON
PHOTOMETRY
POLYCYCLIC AROMATIC HYDROCARBONS
SPECTROSCOPY
STARS
TELESCOPES
AROMATICS
ELEMENTS
FLUIDS
GASES
HYDROCARBONS
NONMETALS
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
PHYSICS
RARE GASES