Preliminary thoughts on SCUSS 1. Scientific perspectives 2. Suggestions for next steps
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Preliminary thoughts on SCUSS1. Scientific perspectives
2. Suggestions for next steps
李 成
SCUSS team meeting, 2011.6.11, Beijing
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Virtues of the u-band for galaxies
• Star formation: – sensitive to young stellar populations
• Cold gas– Indicator of cold gas fraction in galaxies
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1. Estimating cold gas fraction in galaxies
u-r, u-k as indicators
Wei Zhang et al. 2009
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1. Estimating cold gas fraction in galaxies color plus surface brightness
Wei Zhang et al. 2009
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HyperLeda + SCUSS
• >100 HI galaxies from HyperLeda falling in the current SCUSS region
• Expect to have >1000 eventually
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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
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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
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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
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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, …
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WISE preliminary release (Apr 14) Overlapping area: 30<RA<50, 0<Dec<4
SCUSS Year 1
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WISE preliminary release (Apr 14) Overlapping area: 30<RA<50, 0<Dec<4
SCUSS Year 1
Wright et al. (2010)
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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?
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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
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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
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Color-color diagram for star/galaxy separation
图片来自 SCUSS 项目书
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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"
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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