Preliminary thoughts on SCUSS1. Scientific perspectives

2. Suggestions for next steps

李 成

SCUSS team meeting, 2011.6.11, Beijing

Virtues of the u-band for galaxies

• Star formation: – sensitive to young stellar populations

• Cold gas– Indicator of cold gas fraction in galaxies

1. Estimating cold gas fraction in galaxies

u-r, u-k as indicators

Wei Zhang et al. 2009

1. Estimating cold gas fraction in galaxies color plus surface brightness

Wei Zhang et al. 2009

HyperLeda + SCUSS

• >100 HI galaxies from HyperLeda falling in the current SCUSS region

• Expect to have >1000 eventually

2. Star formation in BCGs• Some brightest cluster galaxies show star

formation in their center• How do they get the cold gas: cooling flow or

minor mergers

Jing Wang et al. 2010

2. Star formation in BCGs• Some brightest cluster galaxies show star

formation in their center• How do they get the cold gas: cooling flow or

minor mergers• Cooling flow: a “blue core”– Better to have X-ray image to determine the

thermodynamic state of the gas in the halo center• Minor mergers: more extended u-r color– Estimate the available cold gas in satellite galaxies

• This idea also applies for general early-type galaxies

3. Direct measurements of HOD parameters for different types of galaxies

• Take BCGs as dark matter halo centers• Stellar population synthesis: Identifying

different types of satellite galaxies (SF, AGN, …) and estimating their physical properties

• Measuring the halo occupation number as functions of halo mass and galaxy properties

• Need to carefully subtract contributions from foreground/background galaxies

• Need other bands for better determining the physical properties

Need more bands: UV, IR

• photo-z• Stellar populations, SFH, SFR, stellar mass, …• Identification and classification of different

types of objects• Available data– GALEX, 2MASS, WISE, AKARI, …

WISE preliminary release (Apr 14) Overlapping area: 30<RA<50, 0<Dec<4

SCUSS Year 1

WISE preliminary release (Apr 14) Overlapping area: 30<RA<50, 0<Dec<4

SCUSS Year 1

Wright et al. (2010)

4. Lyman break galaxies magnified by galaxy clusters (?)

• LBG: star-forming galaxies at z~3, R*=24.54, ~1 / arcmin^2 at R=24.5 (Adelberger & Steidel 2000)

• MS 1512-cB58: R=20.4, magnified by ~30 by a foreground cluster (Yee et al. 1996, Seitz et al. 1998)

• Bentz et al. (2004): 6 candidates from SDSS/DR1 QSO sample

• Bentz et al. (2008): HST imaging, all unresolved point sources, 5 quasars, 1 with a companion at 0.8”

• Can we do the same, taking advantage of the much better quality in u-band?

SCUSS Value-added galaxy catalogue (SCUSS-VAGC)

• Collecting data from literature– Previous redshift surveys: CfA, 2dF, SDSS, BOSS– Galaxy clusters: Abell, Zwicky, MaxBCG, GMBCG,

Wen et al., …– HI: HyperLeda, ALFALFA – UV: GALEX– NIR: 2MASS– MIR: WISE– FIR: AKARI

Selection effects for LSS studies

• Survey geometry– Gap between CCDs– Cutout at CCD edges– Bright stars– Bad pixels

• Completeness map– Limiting magnitude varies across the survey region

Color-color diagram for star/galaxy separation

图片来自 SCUSS 项目书

Star/galaxy separation

• 需要仔细比较现有方法，确定最佳方案，尤其是在暗端– SCUSS: DAO sharpness, Bertin g/s– SDSS: m(psf) - m(model) > 0.145 for galaxies– Color-color diagram: u-g vs. g-r

• 需要与已有的更深的图像数据比对– SDSS 使用 COMBO-17 的一块天区： – COMBO-17, S 11: 11h 42m 58s-01 42' 50"

Can we trust SDSS star/galaxy separation for faint sources?

• SDSS: COMBO S11 field as a standard• 100% correct for r<19.5

图片来自 SDSS/DR5 网站

star galaxy