Star Formation in Superthin Galaxies

Superthin galaxies (STs) are low surface brightness galaxies (LSBs) (central surface brightness in B-band > 23 magarcsec−2) with a strikingly high planar-to-vertical axes ratio of ∼ 10−20 with no bulge component. The superthin vertical structure of STGs results in significantly lower values of disc dynamical stability (Jog 1992) and hence higher values of the predicted SFR compared to face-on LSBs. We systematically study the star formation rate (SFR) of samples of STGs and LSBs and compare their relative values. Using GALEX FUV, we estimate the SFR of 212 STGs and 158 LSBs, the median values being 0.057 M /yr and 0.223 M /yr respectively. We next obtain the SFR from WISE (W3) of 549 STGs and 345 LSBs, with median values of 0.471 M /yr and 0.17 M /yr respectively. Finally, from SED fitting of photometric data in ten bands (FUV, NUV of GALEX, u,g,r,i,z of SDSS & J, H, Ks of 2MASS) in MAGPHYS, we find the SFR for a sample of 65 STGs and 103 LSBs to be 0.357 M /yr and 0.616 M /yr respectively. Also, as is indicated by the median values of number of bursts after tform = 1 and an exponential star formation time scale parameter γ = 0.2 Gyr−1, the SFR remains fairly constant over time. Interestingly, in spite of having low SFR compared to ordinary star-forming galaxies, both superthins and LSBs populate the star forming blue cloud region in the specific star formation (sSFR) stellar mass (M*) plane of galaxies.