Long-slit Spectroscopy of Edge-on Low Surface Brightness Galaxies

Abstract

We present long-slit optical spectra of 12 edge-on low surface brightness galaxies (LSBGs) positioned along their major axes. After performing reddening corrections for the emission-line fluxes measured from the extracted integrated spectra, we measured the gas-phase metallicities of our LSBG sample using both the In the luminosity-metallicity plot, our LSBG sample is consistent with the behavior of normal galaxies. In the mass-metallicity diagram, our LSBG sample has lower metallicities for lower stellar mass, similar to normal galaxies. The stellar masses estimated from z-band luminosities are comparable to those of prominent spirals. In a plot of the gas mass fraction versus metallicity, our LSBG sample generally agrees with other samples in the high gas mass fraction space. Additionally, we have studied stellar populations of 3 LSBGs which have relatively reliable spectral continua and high signal-to-noise ratios, and qualitatively conclude that they have a potential dearth of stars with ages < 1 Gyr instead of being dominated by stellar populations with ages > 1 Gyr. Regarding the chemical evolution of our sample, the LSBG data appear to allow for up to 30% metal loss, but we cannot completely rule out the closed-box model. Additionally, we find evidence that our galaxies retain up to about 3 times as much of their metals compared with dwarfs, consistent with metal retention being related to galaxy mass. In conclusion, our data support the view that LSBGs are probably just normal disk galaxies continuously extending to the low end of surface brightness.

Oxygen Loss from Simulated Galaxies and the Metal Flow Main Sequence: Predicting the Dependence on Mass and Environment

“…In this work we have, for the first time, investigated the effect of environment on the fraction of metals lost from galaxies. In addition to reproducing the trend of lower mass galaxies losing more metals seen in both observational and theoretical works (Dalcanton 2007;Ma et al 2016;Du et al 2017), we make several predictions, which are summarised below:…”

SDSS J170745+302056: A low-surface-brightness galaxy in a group

“…The remaining designations are the same as those on the left panel. The red crosses on both panels indicate the characteristics of LSB galaxies from Du et al (2017).…”

“…4 indicate the characteristics of edge-on LSB galaxies from Du et al (2017). These galaxies have metallicities, luminosities, and sizes comparable to those of SDSS J170745+302056.…”

UV and NIR size of the HI selected low surface brightness galaxies

“…Since B band is more sensitive to the star formation, such selection of the LSBG sample may cause a bias for the galaxy population with a diffuse star formation structure. Moreover, an average LSBG has a relatively young stellar population and low metallicity (Du et al 2017). The typical stellar mass is much lower than the M * at the similar redshift (Du et al 2020), indicating an early forming stage of the galaxies.…”

“…So the wide field HI survey projects such as ALFALFA (Haynes et al 2011(Haynes et al , 2018, combined with SDSS optical images, would provide us optimal means to obtain a large sample of LSBGs with reliable HI redshift. Our previous series study based on the LSBGs selected from ALFALFA sample with optical surface brightness measured from SDSS images (Du et al 2015;He et al 2019;Du et al 2019) have shown that the LSBGs have much lower metallicity (Du et al 2017), follow the Tully-Fisher relation (Du et al 2019), and have similar mass-light ratios to the high surface brightness galaxies (Du et al 2020). The Hα images of our HI selected LSBG sample also shows that the star formation surface density has a very weak correlation with the gas surface density, the star formation surface density is much lower than the prediction of Kennicutt-Schmidt law (Kennicutt 1998;Kennicutt & Evans 2012), leading to a significantly longer gas depletion time scales, and low star formation efficiency (Lei et al 2018(Lei et al , 2019.…”