THE EMISSION BY DUST AND STARS OF NEARBY GALAXIES IN THEHERSCHELKINGFISH SURVEY
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abstract
Using new far-infrared imaging from the Herschel Space Observatory with
ancillary data from ultraviolet to submillimeter wavelengths, we estimate the
total emission from dust and stars of 62 nearby galaxies in the KINGFISH survey
in a way that is as empirical and model-independent as possible. We collect and
exploit these data in order to measure from the spectral energy distributions
(SEDs) precisely how much stellar radiation is intercepted and re-radiated by
dust, and how this quantity varies with galaxy properties. By including SPIRE
data, we are more sensitive to emission from cold dust grains than previous
analyses at shorter wavelengths, allowing for more accurate estimates of dust
temperatures and masses.
The dust/stellar flux ratio, which we measure by integrating the SEDs, has a
range of nearly three decades. The inclusion of SPIRE data shows that estimates
based on data not reaching these far-IR wavelengths are biased low. We find
that the dust/stellar flux ratio varies with morphology and total IR
luminosity. We also find that dust/stellar flux ratios are related to gas-phase
metallicity, while the dust/stellar mass ratios are less so. The substantial
scatter between dust/stellar flux and dust/stellar mass indicates that the
former is a poor proxy of the latter. Comparing the dust/stellar flux ratios
and dust temperatures, we show that early-types tend to have slightly warmer
temperatures than spiral galaxies, which may be due to more intense
interstellar radiation fields, or to different dust grain compositions.
Finally, we show that early-types and early-type spirals have a strong
correlation between the dust/stellar flux ratio and specific star formation
rate, which suggests that the relatively bright far-IR emission of some of
these galaxies is due to ongoing star formation and the radiation field from
older stars.
