Thirty years ago, Sérsic & Pastoriza (1965, 1967) drew attention to the fact that galaxies containing ``peculiar'' or ``hot-spot'' nuclei are almost exclusively barred (but see the criticism by Heckman 1978). Using a small sample of galaxies having optical spectra, Heckman (1980) found that barred galaxies more frequently have nuclei showing signs of recent star formation. More evidence came from follow-up spectroscopic observations of objects selected from the Markarian surveys: both Huchra (1977) and Balzano (1983) found evidence for an excess of barred morphologies among starburst galaxies relative to the field galaxy population.
De Jong et al. (1984)
noticed that optically-selected barred spirals tend
to have higher infrared (IR) luminosities and hotter 100 to 60
µm colors
(as measured by IRAS) than their unbarred counterparts. Similarly,
Hawarden et al. (1986)
discovered that more than one-third of
barred spirals emit excess radiation at 25 µm; although the coarse
IRAS beam could not constrain well the location of the emission within
each galaxy, Hawarden et al. postulated that it emanates from circumnuclear
regions with enhanced star formation.
Puxley et al. (1987)
confirmed through radio observations that the emission is confined
mainly to the central 1-3 kpc. In a ground-based 10 µm
survey of the central regions of IR-luminous galaxies,
Devereux (1987)
found that ~ 40% of
early-type barred spirals have enhanced 10 µm emission.
Devereux showed that the emission is compact
(
1 kpc) and that these
sources exhibit a 25 µm color excess (S25µ
/ S12µ
2.5)
similar to that seen in the objects studied by
Hawarden et al. (1986).
That the enhanced radiation in the centers of barred galaxies is powered predominantly by star formation and not nonstellar activity was demonstrated by Devereux (1989), who examined the published spectral classification of the objects in the 10 µm survey showing enhanced emission. Hummel et al. (1990) reached a similar conclusion for a sample of barred galaxies having enhanced radio continuum emission.