Two large spectroscopic surveys of galaxies completed in the last decade, the two-degree field galaxy redshift survey (2dFGRS) at the Anglo-Australia Observatory and the Sloan Digital Sky Survey (SDSS) at the Apache Point Observatory, have produced tremendous impact on current extragalactic studies.

Both 2dFGRS and SDSS have made remarkable achievements in the research areas of large scale structures, galaxies, and quasars, and have produced significant impacts on almost every branch of current extragalactic research. However, there still remain many key questions in the area that can be answered only with surveys that can make census of the Universe much better than the SDSS and 2dFGRS. Some key questions are,

1)Important questions with regard to the physical properties of dark energy and dark matter, the neutrino mass, the physical properties of initial density fluctuation in the early Universe etc, which can be addressed with a better determination of large scale structures on scales 100h-1Mpc;

2)The generic predictions of the cold dark matter model, such as ark matter halos and specially subhalos around galaxies, which can be tested with a bigger sample of groups of galaxies combined with future deep imaging surveys (e.g. LSST and Pan-Starrs);

3)Important questions with regard to the physical processes of galaxy formation, such as galaxy interaction, galaxy merging, energy feedback etc, which can be addressed with a denser sampling of structures to a fainter luminosity limit in our local Universe;

4)Important questions with regard to the growth of supermassive black holes and the co-evolution with their host galaxies, which can be addressed with a better sampling of quasars.

The surveys for solving these key problems can be accomplished with the LAMOST telescope which has a large aperture, a large field of view, and more importantly is quipped with 4000 fibers. Here we propose to undertake the following spectroscopic surveys in 8000 square degrees of the north galactic cap (NGC) and in 3500 square degrees of the south galactic cap (SGC) with the LAMOST telescope,

a)LAMOST Galaxy Deep Survey—Spectroscopic survey of 2.3 million galaxies to a magnitude r= 19.5 in selected areas of 3400 square degrees at NGC and SGC. The spectra will be taken with the exposure time of 1.5 hours during dark nights;

b)LAMOST Galaxy Shallow Survey— Spectroscopic Survey of 2.4 million galaxies to a magnitude r= 19.0 in the area of 8100 square degrees other than that covered by the LAMOST Galaxy Deep Survey. The spectra will be taken with the exposure time of 30 minutes;

c)LAMOST Early Massive Galaxy Survey— Spectroscopic Survey of 1 million intrinsically bright and massive galaxies to a magnitude ideV= 20, with the exposure time set to be the same as those of LAMOST Galaxy Deep and Shallow surveys in the same sky area.

d)LAMOST Quasar Survey Spectroscopic Survey of 0.6 million quasars (1 million candidates) to a magnitude i = 20.5, with the exposure time set to be the same as those of LAMOST Galaxy Deep and Shallow surveys in the same sky area. The quasars will be selected using five band SDSS photometry and UKIDSS infrared photometry where available.

With the completion of these surveys, we will construct a database of 6.3 million spectra of extragalactic objects, the largest database of spectra which will be a huge asset for the world extragalactic research. We believe that the key questions listed above will be successfully addressed, and a number of important discoveries beyond SDSS and 2dFGRS will be made with this database in the research areas of large scale structures, galaxy formation and quasars.

(Refer to "LAMOST ExtraGAlactic Surveys—LEGAS, Proposed by the Working Group on LAMOST Extragalactic Surveys, June 11 2009)