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

TL;DR

This study compares star formation rates in superthin and low surface brightness galaxies, concluding that their intrinsic star formation is similar and differences are mainly due to orientation effects.

Contribution

It provides evidence that superthin galaxies are essentially low surface brightness galaxies viewed edge-on, based on star formation rate analysis using multi-wavelength data.

Findings

Median SFRs are similar for both galaxy types.

Inclination and opacity effects influence observed SFRs.

Superthin galaxies are likely LSBs seen edge-on.

Abstract

Superthin galaxies (STs) are edge-on disc galaxies with strikingly high planar-to-vertical axes ratios of $\sim 10 - 20$ with no bulge component, and central surface brightness in $B$-band $>$ 23 mag arcsec$^{-2}$ comparable to low surface brightness galaxies (LSBs). Although STs and LSBs have similar dynamical, stellar and atomic hydrogen (HI) 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 ten bands including GALEX: FUV, NUV, SDSS: u,g,r,i,z \& 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} $ $M_{\odot}yr^{-1}$ \& $0.2^{+0.9}_{-0.2}$ $M_{\odot}yr^{-1}$ 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.