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Register a new userThe properties of a large volume-limited sample of face-on low surface brightness disk galaxies
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We select a large volume-limited sample of low surface brightness galaxies (LSBGs, 2,021) to investigate their statistical properties and their differences from high surface brightness galaxies (HSBGs, 3,639) in details. The distributions of stellar masses of LSBGs and HSBGs are nearly the same and they have the same median values. Thus this volume-limited sample have good completeness and further remove the effect of stellar masses on their other properties when we compare LSBGs and HSBGs. We found that LSBGs tend to have lower stellar metallicities, and lower effect dust attenuations indicating that they have lower dust, than HSBGs. The LSBGs have relatively higher stellar mass-to-light ratios, higher gas fraction, lower star forming rates (SFRs), and lower specific SFRs than HSBGs. Moreover, with the decreasing surface brightness, gas fraction increase, while the SFRs and specific SFRs decrease rapidly for the sample galaxies. This could mean that the star formation histories between LSBGs and HSBGs are different, HSBGs may have stronger star forming activities than LSBGs.
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A large sample of low surface brightness (LSB) disk galaxies is selected from SDSS with B-band central surface brightness mu_0(B) from 22 to 24.5 mag arcsec^(-2). Some of their properties are studied, such as magnitudes, surface brightness, scalelengths, colors, metallicities, stellar populations, stellar masses and multiwavelength SEDs from UV to IR etc. These properties of LSB galaxies have been compared with those of the galaxies with higher surface brightnesses. Then we check the variations of these properties following surface brightness.
We study the ages of a large sample (1,802) of nearly face-on disk low surface brightness galaxies (LSBGs) by using the evolutionary population synthesis (EPS) model PEGASE with exponential decreasing star formation rate to fit their multiwavelength spectral energy distributions (SEDs) from far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1-5 Gyr for most of the sample no matter the constant or varying dust extinction is adopted, which are similar to most of the previous studies on smaller samples. This means that these LSBGs formed their majority of stars quite recently. However, a small part of the sample (~2-3%) have larger ages as 5-8 Gyr, meaning their major star forming process may occur earlier. At the same time, a large sample (5,886) of high surface brightness galaxies (HSBGs) are selected and studied in the same method for comparisons. The derived ages are 1-5 Gyr for most of the sample (97%) as well. These may mean that probably these LSBGs have no much different star formation history from their HSBGs counterparts. But we should notice that the HSBGs are about 0.2 Gyr younger generally, which could mean that the HSBGs may have more recent star forming activities than the LSBGs.
We study the spectroscopic properties of a large sample of Low Surface Brightness galaxies (LSBGs) (with B-band central surface brightness mu0(B)>22 mag arcsec^(-2)) selected from the Sloan Digital Sky Survey Data Release 4 (SDSS-DR4) main galaxy sample. A large sample of disk-dominated High Surface Brightness galaxies (HSBGs, with mu0(B)<22 mag arcsec^(-2)) are also selected for comparison simultaneously. To study them in more details, these sample galaxies are further divided into four subgroups according to mu0(B) (in units of mag arcsec^(-2)): vLSBGs (24.5-22.75),iLSBGs (22.75-22.0), iHSBGs (22.0-21.25), and vHSBGs (<21.25). The diagnostic diagram from spectral emission-line ratios shows that the AGN fractions of all the four subgroups are small (<9%). The 21,032 star-forming galaxies with good quality spectroscopic observations are further selected for studying their dust extinction, strong-line ratios, metallicities and stellar mass-metallicities relations. The vLSBGs have lower extinction values and have less metal-rich and massive galaxies than the other subgroups. The oxygen abundances of our LSBGs are not as low as those of the HII regions in LSBGs studied in literature, which could be because our samples are more luminous, and because of the different metallicity calibrations used. We find a correlation between 12+log(O/H) and mu0(B) for vLSBGs, iLSBGs and iHSBGs but show that this could be a result of correlation between mu0(B) and stellar mass and the well-known mass-metallicity relation. This large sample shows that LSBGs span a wide range in metallicity and stellar mass, and they lie nearly on the stellar mass vs. metallicity and N/O vs. O/H relations of normal galaxies. This suggests that LSBGs and HSBGs have not had dramatically different star formation and chemical enrichment histories.
The faint stellar halos of galaxies contain key information about the oldest stars and the process of galaxy formation. A previous study of stacked SDSS images of disk galaxies has revealed a halo with an abnormally red r-i colour, seemingly inconsistent with our current understanding of stellar halos. Here, we investigate the statistical properties of the faint envelopes of low surface brightness disk galaxies to look for further support for a red excess. 1510 edge-on low surface brightness galaxies were selected from the SDSS Data Release 5, rescaled to the same apparent size, aligned and stacked. This procedure allows us to reach a surface brightness of mu_g ~ 31 mag arcsec^-2. After a careful assessment of instrumental light scattering effects, we derive median and average radial surface brightness and colour profiles in g,r and i. The sample is then divided into 3 subsamples according to g-r colour. All three samples exhibit a red colour excess in r-i in the thick disk/halo region. The halo colours of the full sample, g-r = 0.60+-0.15 and r-i = 0.80+-0.15, are found to be incompatible with the colours of any normal type of stellar population. The fact that no similar colour anomaly is seen at comparable surface brightness levels along the disk rules out a sky subtraction residual as the source of the extreme colours. A number of possible explanations for these abnormally red halos are discussed. We find that two different scenarios -- dust extinction of extragalactic background light and a stellar population with a very bottom-heavy initial mass function -- appear to be broadly consistent with our observations and with similar red excesses reported in the halos of other types of galaxies.
We present the properties of a large sample (12,282) of nearly face-on low surface brightness (LSB) disk galaxies selected from the main galaxy sample of SDSS-DR4. These properties include B-band central surface brightness mu_0(B), scale lengths h, integrated magnitudes, colors, and distances D. This sample has mu_0(B) values from 22 to 24.5 mag arcsec^{-2} with a median value of 22.42 mag arcsec^{-2}, and disk scale lengths ranging from 2 to 19 kpc. They are quite bright with M_B taking values from -18 to -23 mag with a median value of -20.08 mag. There exist clear correlations between logh and M_B, logh and logD, logD and M_B. However, no obvious correlations are found between mu_0(B) and logh, colors etc. The correlation between colors and logh is weak even though it exists. Both the optical-optical and optical-NIR color-color diagrams indicate that most of them have a mixture of young and old stellar populations. They also satisfy color-magnitude relations, which indicate that brighter galaxies tend generally to be redder. The comparison between the LSBGs and a control sample of nearly face-on disk galaxies with higher surface brightness (HSB) with mu_0(B) from 18.5 to 22 mag arcsec^{-2} show that, at a given luminosity or distance, the observed LSB galaxies tend to have larger scale lengths. These trends could be seen gradually by dividing both the LSBGs and HSBGs into two sub-groups according to surface brightness. A volume-limited sub-sample was extracted to check the incompleteness of surface brightness. The only one of the property relations having an obvious change is the relation of logh versus mu_0(B), which shows a correlation in this sub-sample.
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