The Bar - enhanced Star - formation Activities in Spiral Galaxies

We use the ratio L FIR /L B and the IRAS color index S 25 /S 12 (both widely used as indices of relative star formation rates in galaxies) to analyse subsets (containing no known AGNs or merging/interacting galaxies) of: (a) the IRAS Bright Galaxy Sample, (b) galaxies from the optically complete RSA sample which have IRAS detections in all four bands, and (c) a volume-limited IR-unselected sample. We confirm that IR-bright barred (SB) galaxies do, on average, have very significantly higher values of the FIR-optical and S 25 /S 12 ratios (and presumably, higher relative star formation rates, SFR) than that do unbarred ones; the effect is most obvious in the IR colors. We also confirm that these differences are confined to early-type (S0/a-Sbc) spirals and are not evident among late-type systems (Sc-Sdm). Unlike others, we see no enhancement of the SFR in weakly-barred (SAB) galaxies. We further confirm that the effect of bars on the SFR is associated with the relative IR luminosity and show that it is detectable only in galaxies with L FIR /L B > ∼ 1/3, suggesting that as soon as they have any effect, bars translate their host galaxies into this relatively IR-luminous group. Conversely, for galaxies with L FIR /L B below∼ 0.1 this lu-minosity ratio is lower among barred than unbarred systems , again confirming and quantifying an earlier result. Although there is no simple physical relation between HI content and star formation, a strong correlation of HI content with the presence of bars has been found for early-type spirals with L FIR /L B > ∼ 1/3. This suggests that the availability of fuel is the factor determining just which galaxies undergo bar-induced starbursts.