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Paper: The Local 8-micron/Far-Infrared Relation from SWIRE/SDSS Star-Forming Galaxies
Volume: 381, The Second Annual Spitzer Science Center Conference: Infrared Diagnostics of Galaxy Evolution
Page: 332
Authors: Monkiewicz, J.A.; Dickinson, M.E.; Davoodi, P.; Oliver, S.; Tremonti, C.A.; Chary, R.
Abstract: We examine the behavior of galaxy luminosity at 6-9 μm, a region of the MIR which includes contributions from several PAH bands, as a function of total infrared luminosity LIR(8 − 1000μm), using integrated 8 and 70 μm fluxes for star-forming galaxies in the SWIRE/SDSS overlap sample. Our total sample includes 497 galaxies at z < 0.4, with bolometric luminosities between 8.0 < log(LIR/L) < 11.8. We measure fν(8)/fν(70) flux ratios as a function of LIR, and use spectral line indices from the MPA/JHU Value-Added Catalog to study the behavior of our measured relation as function of galaxy metallicity and nuclear activity. We find that nuclear activity does not systematically change the MIR-FIR relation at these wavelengths. However, metallicity does have a strong effect, with galaxies at 12 + log(O/H) < 8.8 exhibiting systematically lower fν(8)/fν(70) flux values. The 8 μm/FIR relation for the entire SWIRE/SDSS sample has an RMS scatter of 0.2 dex (factor of 2); if only sources with approximately solar metallicity are considered, the RMS scatter drops to 0.128 dex (≈ 30%). A comparison with pre-Spitzer spectral templates suggests that empirical refinements can be made which would improve the agreement of the MIR/FIR ratios. This low-redshift recalibration may be important when interpreting MIPS 24 μm observations of galaxies at z ∼ 2.
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