LAMOST 补充星系样本和LAMOST-SDSS星系对样本

沈世银上海天文台

LAMOST 星系巡天计划 North Galactic Cap

Complementary galaxy sample

South Galactic Cap Main galaxy sample Emission line galaxy

Two complete fields(Wu Hong)

Complementary galaxy sample

SDSS main sample galaxies r<17.77 Spectroscopic completeness

>90% ~7% missed due to fiber

collision effect Input catalog of LAMOST

68,722 objects Biased towards (small scale)

high density environment, e.g. galaxy pair, triplet/quartlet, compact group

Galaxy pair sample in SDSS are strongly biased towards large separation and low redshift

Current status

Complementary galaxy with LAMOST spectra

DR2 (2011-2014): 3456 Why very small fraction?

Lower priority than QSO targets Few Medium plates

Low S/N

Y3 (2014-2015): 2620

Redshift measurements In DR2, 3456 complementary galaxies have

LAMOST spectra Only 1951 have redshifts measured by LAMOST 1-

D pipeline We developed a new PCA-redshift

measurement code 2796 with redshift measured, increased about

25%

Early science: new galaxy pairs

How to define a galaxy pair?

Non-trivial

P<100kpc dV<500km/s

Galaxy pairs are one of the key ingredients to study the galaxy merging and galaxy interaction.

Galaxy pair sample (Shen et al., 2015) 1,102 galaxy pairs (P<100kpc, dV<500km/s)

Visual inspection

Multiple flag Pair definition: dV<500km/s, Rp<100kpc Physical pair ?

interaction

Multiple system: triplet, group,cluster One of the member within another pair Not complete

Redshift dependent A triplet system with M =-20,-21,-22 mag would be

identified as a triplet, a pair and a single galaxy in the SDSS MG sample (r<17.77) at redshift z=0.05,0.1,0.15 respectively.

Overlap flag Visual inspection

Very close pair (image overlap each other) Photometry not accurate Color bias

Interesting objects Example: an isolated triplet (Feng et al. 2015) See http://

cluster.shao.ac.cn/wiki/index.php/Interesting_object_in_LEGAS_DR1

http://cluster.shao.ac.cn/wiki/index.php/Interesting_object_in_LEGAS_DR2

Discovery of an isolated galaxy triplet (Feng et al. 2015)

Chain-like structureFormed in early time

Early type galaxies with Halpha emissionrecent star formation

Other applications and future Supply the galaxy pair sample Supply redshifts to the galaxy group catalog of

Yang et al. Small-scale galaxy cross-correlation function

(Guo Hong)

Future How much can we finish the spectral survey of the

complementary galaxies? After three years (6000 of 6,8000), only two years left.

LAMOST spectral survey 2? (after 2017)

Two complete fields Ra = 37.8, Dec = 3.4 Ra = 21.5, Dec = −2.20

r<18.1 mag ~5000 galaxies, 25000 point sources 28 plates observed from 2012-2014

Yang et al. in preparation

South Galactic Cap

Main goal of the galaxy survey in design Winter season, good weather

Footprint Dec>-10 & b<-30, 3700 sq deg

Input catalog Main sample galaxies (r<18) ~660 k Blue galaxies (18<r<18.8) ~200 k

Science motivation Large galaxy spectroscopic sample in SGC,

deeper than SDSS main sample galaxies Probe the faint (higher z) star forming galaxies

Current status Only 35,000 (<5%) objects observed in past

four years

We can not finish the galaxy survey in SGC as we designed in 5 years (2012-2017)

How is the spectra quality?

Reasons for the small number of galaxies being observed Fiber assignment

Galaxy PRI < QSO QSO candidates outnumbers galaxy

Will be changed Small number of M plates in EG area

Could not be greatly improved because of requirement of successful rate of spectroscopy Weather condition Other survey (Galactic Anti Center , M31)

Possible Collaboration: TAIPAN Measure redshifts for 500,000 galaxies(r~17) and peculiar

velocities for 50,000 galaxies in the nearby universe on the UKST over a 3.5-year period (2016-2019)

Scientific goal Hubble constant Bulk flow Velocity power spectrum Redshift space distortions Galaxy evolution

LAMOST: extend the Taipan survey into the non-SDSS areas of the northern hemisphere? Spectra quality?

summary There are only about 50,000 galaxies that had

been observed by LAMOST in its first three years ~6000 SDSS missed main sample galaxies

Useful for new galaxy pair identification ~5000 galaxies in two small complete fields ~35000 galaxies in South Galactic Cap Other ~4000 bright galaxies (replicated

observation) The spectra quality is barely acceptable(S/N

~10) for galaxies brighter than r<17 mag Redshift measurement Stellar population?