The Properties Of A Large Sample Of Low Surface Brightness Galaxies

There are two parts of this theme.The properties of low surface brightness galaxies (LSBGs) are summaryed in the first part,including the survey of LSBGs,their formation and evolution and star formation.We present a large sample(12,282) of nearly face-on disc LSBGs selected from the main galaxy sample of SDSS-DR4 in the second part.LSBGs are galaxies that emit much less light per area than normal galaxies.Yet,owing to their faintness compared with the night sky,they are hard to find.Hence their contribution to the local galaxy population has been underestimated for a long time.It has been suggested that LSBGs may comprise up to half of the local galaxy population.The first quantitative suggestion about LSBGs is the so-called Freeman's law.It was noticed by Freeman(1970) that the central surface brightness of 28 out of 36 disc galaxies fell in the range ofμ₀(B)=21.65±0.3 mag arcsec^-2.Some people argue that it is real,others argue that it is selected effects or results of extinction.The surface brightness distributions were bias through the high qualitative surveys.Actually,the range of surface brightness are very wide,it is the selected effect that limit our survey of LSBGs.Following them,various aspects of LSBGs have been investigated from radio band to infrared to near-infrared to optical to ultraviolet.Those include their surface photometry, galaxies formation and evolution,HI gas distribution,metallicity,star formation,stellar populations.Especially,Impey et al.analyses their 693 field low surface brightness galaxies (APM) sample in various morphologies.O'Neil et al.discovered red LSBGs firstly in the "Texas" survey.LSBGs are neither extreme dwarf galaxies nor the remnants of high surface brightness spiral galaxies.They are unevoved systems with low metallicity,low stellar formation rate, small stellar density,a relatively high gas fraction and large amounts of dark matter.Despite these impressive progresses,there are still several challenges about LSBGs,such as many aspects of their formation and evolution,in particular,considerable uncertainty regarding their star formation history and so on.Moreover,the previous studies were based on small sample,up to several hundreds.While the present modern digital sky surveys,Sloan Digital Sky Survey(SDSS),Two Micron All Sky Survey(2MASS),Infrared Astronomical Satellite(IRAS),greatly improve the observed numbers of astronomical objects,and could provide a larger sample of LSBGs,hence giving much more information.Therefore,we propose a project to search for a large sample of LSBGs from the main galaxy sample of SDSS-DR-4 data base,then study their distributions(surface brightness, redshift,disk scale length,B-band absolute magnitude) and relations among them(B-band absolute magnitude and disk scale length,distance and disk scale length,B-band absolute magnitude and distance,and so forth).According to O'Neil et al.(1997),we study their properties by color-color diagram.And make cross-correlations with NIR 2MASS to obtain their optical-NIR color-color,which could break the degeneracy.Then the properties are studied by the optical-NIR color-color diagram.We also select a volume-limited subsample by considering z＜0.1 and brighter than the corresponding M_r to check how the properties change.The comparison between LSBGs and high surface brightness galaxies are presented. There are some differences.We discussed the difference by dividing the total sample into for subsample.