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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 559347.0, MPI für Astronomie / Publikationen_mpia
A simple connection between the near- and mid-infrared emission of galaxies and their star formation rates
Authors:Mentuch, Erin; Abraham, Roberto G.; Zibetti, Stefano
Date of Publication (YYYY-MM-DD):2010
Title of Journal:The Astrophysical Journal
Journal Abbrev.:ApJ
Issue / Number:2
Start Page:1971
End Page:1983
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies common to the Spitzer Infrared Nearby Galaxies Survey and the Large Galaxy Atlas Survey. Pixels from each galaxy are grouped into regions of increasingly red near-infrared colors. As expected, the majority of pixels are shown to have relatively constant NIR flux ratios (log10 I3.6/I1.25 = –0.30 ± 0.07 and log10 I4.5/I3.6 = –0.19 ± 0.02), representing the blackbody continuum emission of main sequence stars. However, pixels with red NIR colors correspond to pixels with higher Hα emission and dust extinction. We show that the NIR colors are correlated to both quantities, with the strongest correlation to the intrinsic Hα emission. In addition, in regions of high star formation, the average intensity of pixels in red-excess regions (at 1.25 μm, 3.6 μm, 4.5 μm, 5.6 μm, 8.0 μm and 24 μm) scales linearly with the intrinsic intensity of Hα emission, and thus with the star formation rate (SFR) within the pixel. This suggests that most NIR-excess regions are not red because their light is being depleted by absorption. Instead, they are red because additional infrared light is being contributed by a process linked to star formation. This is surprising because the shorter wavelength bands in our study (1.25 μm-5.6 μm) do not probe emission from cold (10-20 K) and warm (50-100 K) dust associated with star formation in molecular clouds. However, emission from hot dust (700-1000 K) and/or polycyclic aromatic hydrocarbon (PAH) molecules can explain the additional emission seen at the shorter wavelengths in our study. The contribution from hot dust and/or PAH emission at 2 μm-5 μm and PAH emission at 5.6 μm and 8.0 μm scales linearly with warm dust emission at 24 μm and the intrinsic Hα emission. Since both are tied to the SFR, our analysis shows that the NIR excess continuum emission and PAH emission at ~1-8 μm can be added to spectral energy distribution models in a very straightforward way, by simply adding an additional component to the models that scales linearly with SFR.
Free Keywords:dust; extinction; galaxies: ISM; galaxies: star formation; infrared: galaxies; infrared: ISM; surveys
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2010ApJ...725.1971M [ID No:1]
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