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Abstract:
We present a multifrequency dataset for an optically-selected,
volume-limited, complete sample of 118 late-type galaxies (>S0a)
in the Virgo cluster. The database includes UV, visible, near-IR, mid-IR,
far-IR, radio continuum photometric data as well as spectroscopic
data of H_alpha, CO and HI lines, homogeneously reduced,
obtained from our own observations or compiled from the literature.
Assuming the energy balance between the absorbed stellar light and that
radiated in the IR by dust, we calibarte an empirical attenuation law
suitable for correcting photometric and spectroscopic data of normal
galaxies.
The data, corrected for internal extinction,
are used to construct the spectral energy distribution (SED)
of each individual galaxy, and combined to trace the median SED of galaxies
in various classes of morphological type and luminosity. Low-luminosity,
dwarf galaxies have on average bluer stellar continua and higher
far-IR luminosities per unit galaxy mass than giant, early-type spirals.
If compared to nearby starburst galaxies such as M82 and Arp 220,
normal spirals have relatively similar observed stellar spectra but
10-100 times lower IR luminosities. The temperature of the cold dust
component increases with the far-IR luminosity, from giant spirals to dwarf
irregulars.
The SED are used to separate the stellar emission from the dust emission
in the mid-IR regime. We show that the contribution of the
stellar emission at 6.75 micron to the total emission of galaxies is
generally important, from ~ 80% in Sa to ~20 % in Sc.
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