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LEGAS Science

With the LAMOST, we will be able to complete, in a reasonable time frame (say, 5 years), surveys of galaxies and quasars which exceed existing surveys by a factor of 5∼10 in the number of objects and in the volume probed. With the data obtained in these surveys, we expect to make breakthroughs by solving a number of key scientific questions.

1)The survey volume of the Early Massive Galaxy Survey would probe a volume of about 5 times larger than the one by the SDSS LRG survey. As a result, the error in the measurement of large scale structure power spectrum would be halved. This would greatly improve the precision in the measurement of the matter fluctuation power spectrum, particularly the scale of baryon acoustic oscillation (BAO and the shape of the power spectrum. With such improvement, there is a great potential for making important discoveries or at least putting more stringent constraint on the nature of dark energy, inflation theories, mass of neutrinos, and nature of dark matter;

2)In the nearby Universe, the number of observed faint and dwarf galaxies would be raised by a factor of 10 to a certain faint limit (say Mr =−18.0), and with a comparable increase in the volume probed. This could significantly lower the cosmic variance which dominates the error on the faint end of galaxy luminosity function and clustering properties. For example, the error bar of the two point correlation function for faint galaxies (of 1/10 typical luminosity) could be reduced to one third of its present value. This would help constrain the properties of the dark matter particle, solve the outstanding problems in the formation of dwarf galaxies, and provide information on the energy feedback process in galaxy formation;

3)As fainter galaxies can be observed to a fixed distance, we will have a denser sampling of the large scale structure which makes us easier to identify cosmic webs and quantify more reliably the environments of different types of galaxies. This information is vital for improving our understanding the relation between the environment/galaxy interaction and the observed AGN activity, formation of supermassive black holes, starburst in galaxies, morphology transformation of galaxies (e.g. from spiral galaxy to elliptical galaxy);

4)We will be able to identify a large number of groups of galaxies in the galaxy surveys. For example, the number of groups with more than 10 members is about 104, compared with 103in the SDSS. More importantly, these groups will be at distance of redshift>0.2, which will be essential for studying the galaxy evolution in dense environments, and for revealing the dark matter distribution, including substructure of dark matter when combined with deep imaging observations (e.g. Pan Starrs, LSST);

5)The LAMOST surveys will measure the redshift of galaxies at z ∼0.3 with Mr <−20.5, and also reveal the evolution in galaxy properties over the last 4 Gyr, including the evolution in number density, population, star formation rate, and kinematic parameters. The large sample is again vital, since the evolution of galaxies is relatively slow in the last 4 Gyr, which enables a detailed study of galaxy formation and evolution;

6)The number of quasar spectra would be increased by a factor of 4, allowing us to obtain the most accurate quasar luminosity function, and to understand better about the quasar evolution from z= 3. At the same time, quasar clustering can be better measured on large scales. This would help to further tighten the constraints on cosmological parameters, particularly the equation of state of the dark energy (from the BAO measurement at z=2) and the primordial non-Gaussianity (from the scale dependence of clustering on largest scales).

7)We plan to select quasars using the UKIDSS infrared photometry in addition to the SDSS five band photometry. Since the UKIDSS-SDSS selected sample of quasars would not be affected by extinction/absorption, we will be able to uncover a large population of obscured quasars which were otherwise missed in the SDSS QSO survey. With such a sample, we will test the unified model of AGN, and study the growth process of the supermassive black holes, the nuclear regions, host galaxies and the dust/gas property of the intervening galaxies. The quasar luminosity function could be better determined, and combining with other observations of cosmic star formation rate, we could study the co-evolution of galaxies and their central black holes.

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