paper

Dust emission in the far-IR as a star formation tracer at z=0: systematic trends with luminosity

arXiv:astro-ph/0308366 · doi:10.1111/j.1365-2966.2003.07126.x

Abstract

We investigate if dust emission in the far-IR continuum provides a robust estimate of star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40--1000 micron luminosity (L_dust) to the far-UV (0.165 micron luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 micron limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K-band (2.2 micron) luminosity, morphology and inclination (i). This sample shows that the ratio of L_dust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K-band luminosity. We find that L_dust/L_FUV is proportional to e^(-tau_K) (alpha+0.62) (L_K)^(0.62), where L_FUV and L_K are the unattenuated stellar luminosities in far-UV and K, respectively, and alpha is the ratio of the attenuation optical depths at 0.165 micron (tau_FUV) and 2.2 micron (tau_K). This relation is to zeroth order independent of i and morphology. It may be further expressed as L_dust/L_FUV proportional to (L_K)^delta, where delta = 0.61 - 0.02 alpha, under the observationally-motivated assumption that, for an average inclination, e^(-tau_K) is proportional to (L_K)^(-0.02). We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle averaged values of alpha. We find that delta is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. (Abridged)

8 pages, 2 figures, accepted for publication in MNRAS

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