大天区面积多目标光纤光谱天文望远镜

The Large Sky Area Multi-Object Fiber Spectroscopic Telesc

ope(LAMOST)

The Scientific Case For LAMOST

Basic parameters of LAMOST

• 4-meter Schmidt telescope• The declination of observable sky area ranges

from -10 to +90.• 20 square degree of the FOV• 4000 fibers• Spectrum resolution: VPH (Volume Phase Holographic) Grating R=1000, 2000, 5000, 10000

Grating Blue branch

Red branch

R

1000 3700-

5900 Å

5700-

9000Å

binning 500

- 1000

narrow slit

2000

5000 4100-

4400Å

8300-890

0Å

- 5000

narrow slit

10000

Resolution powers

LAMOST was designed primarily as an efficient redshift engine

• Challenge: After 2dF and SDSS• Opportunity: the gap of between number with and without spectral

data still grow up The requirement of spectroscopic observation for

large number of objects in large sky area is more urgent than ever before

• Next generation Large telescope need large survey data set to find interested objects

How can we do better than 2dF and SDSS

• Large Aperture• Large field of view• More fibers What we try to do:• increasing the spectral resolution • Carefully select the targets• better sky subtraction • spectrophotometer

Key Projects

• Extra-galactic spectroscopic survey —

Galaxy and QSO redshift survey

• Stellar spectroscopic survey —

Structure of the Galaxy, and so on.

• Cross identification of multi-waveband survey.

• 1999.12 LAMOST 与银河系的结构的演化讨论 （北京香山）

• 2001.11 2dF 与 SDSS 巡天结果讨论会 （北京国台）• 2003.9 LAMOST 科学目标小型研讨会 （北京国台）• 2003.9 多波段河外巡天观测研讨会 （河北张北）• 2003.11 LAMOST 与银河系研究专题研讨会 （浙江杭

州）• 2004.8 LAMOST 与银河系结构与演化研讨会 （吉林延

吉）• 2005.4 LAMOST 科学目标研讨会（ 2005 ） （江西井

冈山）• 中德、中法、中英双边科学研讨会• 成立了 LAMOST 科学目标工作小组

LAMOST survey strategy

• general survey vs. surveys with specific purpose?

• complete coverage vs. large effective volume?

• Tracers (color selected high redshift galaxy? quasar?)

• optimal scale for survey• competition with other survey:

Strategies of galaxy redshift survey

• Magnitude limited (B=20.5) sample

Intrinsic faint object with mean z=0.2

• Luminous Red Galaxy (LRG)

Deep: 0.3 < z < 0.8

Redshift survey of Galaxy

Low Resolution spectroscopy:

• To obtain the spectra of faint celestial objects (Galaxy and AGN) down to 20.5m with 1nm spectral resolution in 1.5 hours exposure.

• Wavelength range: 370—900 nm

• Dark night

Sky Coverage

Advantage over small survey

• Cosmic variance

• Finite Sampling

• Edge Effect

Disadvantage for the large Sky Area Survey

• Long time projects

LOCAL REDSHIFT SURVEY After 2dF and SDSS

• Make big local leaps in survey size/volume

• Galaxy clustering depend the subset of galaxies: color, luminosity, type,…

• The redshift-space distortion of the large-scale clustering

• Topology of Large Scale Structure

Clustering per Spectral Type

Correlation functions Correlation functions (Madgwick el al. 2003) (Madgwick el al. 2003)

Stochastic biasing Stochastic biasing (Wild et al. 2004)(Wild et al. 2004)

To measure higher-order clustering statistics of the galaxy distribution

– determine the bias parameter b, revealing the relationship between the distributions of mass and light and yielding a direct measure of Ω.

– establish whether the galaxy distribution on large scales is a Gaussian random field, as predicted by most inflationary models of the early universe

– investigate the non-linear growth of clustering in the small-scale galaxy distribution.

Cluster of galaxies

• Cataloged of cluster of galaxies and supercluster

• Space distribution of cluster and superclusters

• Compare with x-ray selected cluster of galaxies

• Cluster evolution

Calibrating the Photo-z sample

• SED (Spectrial Energy Distribution)

• Redshift error distribution

In order to calibrating the photo-z sample, we need the similar color and magnitude range spectroscopic redshift sample

Baryon oscillations

• provide a standard rod for mapping the evolution of the geometry of the universe with redshift

• measure the equation of state of the dark energy

BARYON ACOUSTIC PEAK IN THE LARGE SCALE CORRELATION FUNCTION OF

GALAXIES

Effect of the survey window function

Gravitational Lensing• Combine the high quality image of the lensing galax

y with powerful spectroscopy capabilities of LAMOST to conduct a deep wide-field spectroscopic sample of all these galaxies, it will be very helpful for the test of the distribution of Dark matter

LRG sample

Advantage to select LRG• Red color → easy to find the candidate• Most luminous galaxy → Map large

cosmological volume• Correlated with cluster

→ To detect and study the clustering

• The SDSS colour selection of LRGs is very efficient, so it could be make an large cosmological volume sample with high completeness and reliability..

• Complementing to SDSS LRGs sample up to r < 20.5, to get galaxy redshift sample with 0.38 < z < 0.8 .

• Overlap in redshift space between Galaxy and QSOs

• Scientifically, there is a great benefit in having the two new surveys (Galaxy and QSOs) co-extensive since there is now a substantial overlap in redshift space, providing opportunities to compare the clustering and environments of the two classes of object.

High resolution spectrum for LRG

• With VPH grating we may get the resolution up to R=5000-10000

• Line profiles information for the absorption line like CaII H & K, [OH]……

• Diagnostic of Galaxy dynamic, star formation AGN activity

GALAXY FORMATION

AND

EVOLUTION

Large Number of the galaxy Sample

• When the objects are very faint, thousands of objects of the same type will need to be avarange to detect the required spectral feature

Stellar Populations in Low-Redshift Galaxies

• Characterize the stellar pops and star-formation histories of the current galaxy population as a function of properties and environment at low-z

• survey to characterize the stellar populations of galaxies (age, metallicity, star-formation history) as a function of global properties (luminosity, morphology, mass) and environment (local density/structures)

Old Stellar Populations at Early Epochs

• Ages and metallicities of stellar populations in luminous red galaxies as a function of mass (velocity dispersion) at early epochs, from 0.45<z<0.7

• Goal: study formation and evolution of the oldest stellar populations by observing luminous red galaxies (LRGs) over 0.45<z<0.7 (follow-up of 2dF-SDSS

• Method: obtain spectra at ~1Å resolution and S/N>30 to measure spectral indices (ages, metallicities, SFR histories) and velocity dispersions (masses); long time baseline resolves age-metallicity degeneracy in spectra

Emission line galaxies survey

• Low metallicity blue compact galaxies

• H II galaxies

• Star-forming galaxies

• Ly-break galaxies

• QSO2

QSO survey

• Combine the high quality digital image data of SDSS (5 colors) with powerful spectroscopic capabilities of LAMOST to conduct a deep wide field spectroscopic suevey for Quasars

• Evolution of the quasar luminosity function• Spatial clustering of quasars as a function of Reds

hift• Redshift distortion of the Quasar space distributio

n• Discover the high Redshift QSOs:

use g ,z band color to find QSO with z>3 up to 6

use IR color J.K.H. band color ( K~20) to find QSOs with z>7

K-excess selected QSO: obscured by dust.• Cross correlation between the QSOs and the foreg

round galaxies and cluster of galaxies:

QSO absorption studies

• The clustering statistics of Lyman alpha absorption system

Galactic Structure

and

Evolution

• It is evident that our own Milky Way galaxy is the only galaxy that we can presently study at sufficiently high spatial (and kinematical) resolution, and at sufficient depth, to address many of the open questions on the physics of galaxy formation

• Stellar spectroscopy plays a crucial role in the study of our Galaxy, not only providing a key component of the 6-dimensional phase space of stellar positions and velocities, but also providing much-needed information on the chemical composition of individual stars. Taken together, information on space motion and composition can be used to unravel the formation process of the Galaxy.

Galactic Structure

LAMOST will be able to detect and characterise stars in all of the major components of the Galaxy down to a magnitude limit of V~18 at low spectral resolution R=1000

or

Middle spectral resolution for bright stars

R=5000 - 10000

Sloan Extension for Galactic Underpinnings and Evolution

(SEGUE)This project include both imaging and spectroscopy: The spectroscopy survey will obtain ~ 250,000 spectra of

Galactic stars, with plates spread out across Galactic latitude and longitude. These observations consist of two plates at each of 200 directions (400 plates total). Each direction would include one 45-minute plate, similar in depth to the current SDSS survey, and one 1.5-hour, double-length plate. The deeper plates will yield S/N ~ 15 for objects as faint as g ~ 20.3, and S/N > 50 for g ~ 18.5, to increase the accuracy of the metallicity (and radial velocity) determinations for the fainter stars in each of the pointings.

Complementary to SEGUE

• Obtain radial velocities with 15 km/s precision available for stars to v=20 magnitude

• Measure key spectral features of stars:

g-band, Fe lines, Ca H&K, H-beta and other Balmer lines, Ca triplet.

• Radial velocities, combined with proper motions and photometric parallax when available give all 6 kinematic phase space coordinates. This opens up the possibility of exploring velocity ellipsoids of the components of the Galaxy

Characterization of component structures of stars in the Milky Way • We aim to define and characterize the co

mponent structures of the stellar populations in the Milky Way

• Galactic structure beyond the simple thin disk, thick disk, and spheroid model

moving groups and coherent streams

a set of stars that may be part of the merger that puffed up the thick disk, overdensities of stars over the Galactic bar a metal-weak thick disk

Density, kinematics, and chemistry of coherent structures in the Galaxy • We would plan to trace the stream around

the Galaxy, study its stellar dynamics, and obtain information on the chemical abundances of its constituent stars

The merger history of the Galaxy

• To identify streams as spatial overdensities, moving groups, and star groupings with similar metallicities/ages as determined from spectroscopic classifications of stars

• The number and inferred extent of identified substructures will be used to constrain the total number of mergers and typical sizes of the merged structures.

Chemical evolution of the Milky Way

• Elemental abundances of stars are crucial for identifying stellar populations, chemical history of the Milky Way, and ultimately discovering the Milky Way’s formation mechanism

Dark matter clumpiness in the Milky Way

• By tracing the structure and kinematics of stars in our own Galaxy, we should be able to identify and characterize any existing structure in the dark matter distribution in our Galaxy

Mode 2: Middle resolution spectroscopy for Stellar and The Galaxy data

• Resolution power R=10000 over 850-875nm • The wavelength interval is remarkably free from t

elluric lines and it is centered on the triplet of Ca II, the head of hydrogen Paschen series and several strong metallic lines

• It offers valuable spectral classication opportunities as well as useful diagnostic tools in stellar evolution galactic population studies and chemical abundance analysis

All sky survey for stars bright than V=16

• ∆Vr : ≤2km/s

• ∆[Fe/H] : ≤0.2dex• ∆[/H] : ≤0.2dex

• ∆Teff : ≤100K

• ∆log g : ≤0.2dex

• Complement to the GAIA survey to study the structure and evolution of our Galaxy

Cross identification with other multi-waveband survey

To provide a massive spectroscopic database for use in conjunction with other surveys, for finding rare and interesting types of object, and as a source for a wide variety of follow-up observations.

•Welcome to use LAMOST in the future