LAMOST Extragalactic
Surveys (LEGAS)
Yipeng Jing
Shanghai Astronomical Observatory
For the LEGAS working group
Main Parameters
• Main function
spectroscopic sky survey
• Effective aperture
4 meter
• Focal length
20 meter
• Angular FOV
5（linear FOV 1.75-meter）
• Image quality
80% energy encircled in 2.0 acrsec
• Number of optical fiber
4000
• Observing sky area
-10 +90
24,000 square degrees
• Spectral resolution
• Survey capability
1-0.25nm
taking spectral resolution 1nm,
integration time 1.5 hours,
• Size of fiber
max bj magnitude: 20.5m at Xinlong
3.30 arcsec（ 320m linear）
Task: make a proposal
Contributions to LEGAS proposal
• Working Group:
– Members: Jing Yipeng, Zhou Xu, Chen Xuelei, Wu Hong, Wu
Xuebing, Zheng Xianzhong,Shen Shiyin, Wang Junxian, Li Cheng,
Fan Xiaohui
– LAMOST engineering contacts: Zhang Haotong, Zhang Yanxia,
Luo Ali, Chen Jianjun.
• Wang Tinggui, Chu Yaoquan, Kong Xu, Yang Xiaohu,
Zheng Zheng, Zhang Pengjie, Yuan Weimin, Gao Yu, Jun
Pan, Zhou Hongyan, Shang Zhaohui, Lu Youjun,
XiaXiaoyang, Liu Fengshan, Wang Jianling, Liang
Yanchun, Zhang Wei, Fan Zuhui, Zhang Xinmin, Li Hong,
Wang Yougang, Wu Fengquan…..(incomplete)
• 60 staff members + >120 students and postdocs in China
are expected to analyze the LEGAS data
Cutting-edge problems for
LAMOST (I)
• The physical properties of dark energy, 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 100 h−1Mpc;
• The generic predictions of the cold dark matter
model, such as dark matter halos and
especially subhalos around galaxies, which can
be tested with a bigger sample of groups of
galaxies combined with future deep imaging
surveys (e.g. Pan-Starrs and LSST) ;
Cutting-edge problems for LAMOST (II)
• 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;
• The growth of supermassive black holes and
the co-evolution with their host galaxies,
which can be addressed with a better
sampling of quasars at z=1-3 and a larger
sample of low-z AGNs.
Proposed LEGAS Surveys (the
most optimistic)
• Spectroscopic Surveys of galaxies and QSOs
in the NGC of 8000 sq degrees (SDSS sky)
and in the SGC of about 3500 sq degrees:
– LAMOST Galaxy Deep Survey; 2.3 million of
r<19.5 in 3400 sq deg;
– LAMOST Galaxy Shallow Survey; 2.4 million of
r<19.0 in the rest 8100 sq deg；
– LAMOST Early Massive Galaxy (EMG) Survey; 1
million of ideV<20.0 ；
– LAMOST Quasar Survey; 0.4 million of i<20.5;
• A data base of 6 million extragalactic spectra
Pilot surveys
• 140 square degrees sky areas at high
Galactic latitude
– r<19.5 galaxies (800/deg**2)
– i<20 EMGs (100/deg**2)
– 19.1<i<20.5 point sources (2000/deg**2)
40 dark nights
• 120 regions of rich clusters for early
science +calibration in ALL LEGAS region
• Determine how many transparent nights
are available for LEGAS each year?
Another LEGAS proposal
• The current one:
– Competition from SDSS III on EMGs
– According to the telescope design parameters
• A “descoped” one, but still unique and very
powerful:
– Shallow survey (r<19) in 11000 square degrees (3.8
million)
– QSO survey (19.1<i<20.5) (0.6 million)
– Exposure time: 30 minutes
– 3.3 years; 90 % complete for galaxies and 100%
complete for QSOs; fiber usage rate is 56%
Shen Shiyin
provides
Science Case 1. Clustering of galaxies
on the largest ever scales
•
Will combine LRGs, QSOs and galaxy
samples to explore the clustering of galaxies
on large scales (>50 Mpc/h), including BAO.
The results will give new constraints on dark
energy, inflation theories, Non-Gaussianity,
modified gravity, and neutrinos mass;
Simulations of NGC EMGs
距今42亿年
SLOAN 2
Two-point CF
SLOAN 2
LAMOST
Cheng LI
距今67亿年
LAMOST
赤道两侧3度范围内的亮红
星系的分布情况（模拟）
Constraining the EOS of dark
energy, e.g.,w(z)=w0+w1 z/(1+z)
Wang,X, Chen,X et al.
Hong LI et al.
Science Case 2. Delineate filaments and
study the environment dependence of
galaxies
Zhang et al. (2009)
Case 3. Formation of dwarf
galaxies
• Filamentary structures in the Universe are
delineated with the dense sampling;
• Understanding why dwarf galaxies have
(or do not have ) formed, compared with
LCDM (feedback processes)
• May constrain the properties of dark
matter particles
LAMOST主星系样本预研究
距今24亿年
星
系
的
分
布
SLOAN
SLOAN
距今49亿年
LAMOST
LAMOST
暗
星
系
样
本
的
两
点
相
关
函
数
Mo et al. (2005)
Distribution of dwarf galaxies（to ALFALFA HI limit）：
CDM vs Warm dark matter（m＝1kev)； halo mass about
10**10 M_sun/h
Zavala, Jing， et al 2009, ApJ
Case 4. quantify dark matter
distribution with groups
• Understanding galaxy property and
evolution in dense environments
• Quantifying dark matter distribution within
groups;
• Combining Pan Starrs or LSST, may be
feasible to explore subhalos
Case 5: Reveal the evolution of galaxies in
the last 4 billion years (15 times GAMA)
4 billion years
LAMOST
Case 6: HOD of different galaxies
• Measuring the clustering and abundance
of galaxies with different properties;
• Obtain Occupation Distribution of different
galaxies in dark matter Halos (HOD)
• Study the evolution of galaxies from the
HOD at different redshifts
HOD method:
assuming N
galaxies in halo
of mass M；
First applied to
Las Campanas
Redshift survey，
getting alpha＝
0.09
Jing, Mo,
Boerner 1998,
ApJ, 494, 1
不同质量暗物质晕内部的
星系光度函数
Conditional luminosity functions of galaxies inferred from the
best-fit HOD parameters for the luminosity-threshold samples,
shown at three different halo mass scales
Idit Zehavi et al., ApJ, 630:1–27, 2005 ; Yang et al 2003 for 2dF
（a）亮红星系的投
影两点相关函数；
（b）不同质量暗物
质晕内部的亮红星系
数目等
（c）卫星星系的比
例
（d）
Projected two-point auto-correlation functions and bestfit HODs for the two luminosity-threshold LRG samples.
Zheng Zheng ,…,JYP, et al., to be published
Case 7: QSO Luminosity Function
and evolution
•
obtain the most accurate quasar
luminosity function, and to understand
better about the black hole assambly
from z = 3
•
Will probably detect the luminosity
dependence of QSO clustering, and be very
powerful to study the coevolution of galaxies
and central black holes
Will be an ideal sample to explore BAO and
LSS at z=2, for constraining DE and physics of
the Early Universe
•
Richards,G
Case 8: uncover obscured QSOs
• Since part of the QSO sample will be
based on UKIDSS-SDSS , it is very useful
for studying obscured quasars, testing the
unified model of AGN and constraining the
growth history of super massive black
holes;
• These cases are only examples!!! The list
is not exclusive
• In SDSS, only half of the discoveries had
been anticipated
Final Remarks and next steps
• SDSS II and 2DF have made great
achievements in studying galaxy formation
and cosmology.
• LAMOST, if can reach its design
specifications, will definitely make many
remarkable achievements in extragalactic
astronomy in the post-SDSS(II) era;
The input sources only include
galaxy(r<19) and QSO(i<20.5).
There are about 3.8 million galaxies and
0.6 million QSOs, each of them is set
with an exposure time 0.5h.
It takes about 3 years and 3 months to
reach the completeness of 90%.
The average fiber usage is 56%.
Since the priority of QSO is higher than
galaxy, the completeness of QSO is
about 100%.
The surveys will be elaborated after
the pilot survey data
Thank you!