Are superthin galaxies low-surface-brightness galaxies seen edge-on? The star formation probe

Abstract

ABSTRACT Superthin galaxies (STs) are edge-on disc galaxies with strikingly high planar-to-vertical axes ratios of ∼10–20 with no bulge component, and central surface brightness in the B band > 23 mag arcsec−2 comparable to low-surface-brightness galaxies (LSBs). Although STs and LSBs have similar dynamical, stellar, and atomic hydrogen (H i) masses on an average, it is tricky to conclude if they constitute the same galaxy population, given the edge-on and face-on orientations of the STs and the LSBs, respectively. We systematically study star formation rate (SFR) in a sample of STs and LSBs using SED fitting of photometric data in 10 bands including GALEX: FUV, NUV, SDSS: u,g,r,i,z and 2MASS: J, H, Ks using stellar population synthesis models employing the publicly available software magphys (Multi-Wavelength Analysis of Galaxy Physical Properties). The estimated median SFRs for LSBs and STs are $0.4^{+2.2}_{-0.3}$$ and $0.2^{+0.9}_{-0.2}\, {\rm M}_{\odot }{\rm yr}^{-1}$, respectively. Our calculations indicate that this deficit in the SFR of an ST can be attributed to inclination and opacity effects. Therefore, we conclude that STs and LSBs have equal intrinsic SFR over and above other physical properties, which possibly implies that STs are just LSBs seen in edge-on.