Understanding the Chemical Evolution of Blue Edge-on Low Surface Brightness Galaxies

We present a sample of 330 blue edge-on low surface brightness galaxies (ELSBGs). To understand the chemical evolution of ELSBGs, we derived the gas-phase abundance and the [ α /Fe] ratio. Compared with star-forming galaxies, ELSBGs show a flatter trend in the mass–metallicity ( M _* – Z ) relation, which suggests that the oxygen abundance enhancement is inefficient. We focused on 77 ELSBGs with H i data and found that the closed-box model cannot explain their gas fraction and metallicity relation, which implies that infall and/or outflow is needed. We derived the [ α /Fe] ratio of normal ELSBG ( = 10 ^9.5 M _⊙ ) using single stellar population grids from the MILES stellar library. The mean [ α /Fe] ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We suggest that the long timescales of star formation and/or metal-rich gas outflow events caused by SNe Ia winds are likely to be responsible for the α -enhancement of massive ELSBGs.