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Date and Time of the Query: 2019-04-25 T09:24:55 PDT
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For refcode 1989ApJ...342..759T:
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1989ApJ...342..759T FAR-INFRARED EMISSION AND STAR FORMATION IN SPIRAL GALAXIES G. TRINCHIERI, G. FABBIANO, AND R. BANDIERA Received 1987 December 28; accepted 1988 December 29 ABSTRACT We present a statistical study of a sample of normal spiral galaxies, which investigates the correlations between the emission in the far-infrared, H{alpha} and blue, together with a comprehensive comparison of other related quantities (optical and infrared colors, and the H{alpha} equivalent width). This study is different from previous ones because it takes into account several different quantities at the same time and can therefore investigate whether correlations among different quantities are directly related to a given astrophysical phenomenon, or are a by-product of more hidden fundamental relations, or merely result from the sampling of galaxies with a large range in size, mass, and luminosity. We find that the luminosities in these three bands are all tightly correlated, although both the strength of the correlations and their functional dependencies are a function of the galaxies' morphological types. The best-fit power laws to these correlations are different for the comparison of different quantities and deviate significantly from linearity in some cases, implying the presence of additional emission mechanisms not related to the general increase of luminosity with galactic mass. We find clear evidence of two independent affects in the incidence of the warm far-infrared emission in late-type spirals. One is a luminosity effect, as shown by the presence of excess far-infrared relative to their H{alpha} or optical emission in the more luminous galaxies, coupled with warmer far-infrared colors. This evidence is interpreted in terms of a warm far-infrared component, produced in highly obscured stardust regions, and present only in high-luminosity objects. The second effect is a dependence on widespread star-formation activity, measured by larger H{alpha} equivalent widths. The present results can be used to set some constraints on the mass function of disk galaxies and indicate that if there is a break (alternatively, if the mass function is bimodal), the change should occur at masses lower than M ~ 1-2 M_sun_. Subject headings: galaxies: interstellar matter - galaxies: photometry - stars: formation
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