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Preliminary thoughts on SCUSS 1. Scientific perspectives 2. Suggestions for next steps

Preliminary thoughts on SCUSS 1. 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 C old gas Indicator of cold gas fraction in galaxies.

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Preliminary thoughts on SCUSS 1. Scientific perspectives 2. Suggestions for next steps

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  1. Preliminary thoughts on SCUSS1. Scientific perspectives2. Suggestions for next steps 李 成 SCUSS team meeting, 2011.6.11, Beijing

  2. Virtues of the u-band for galaxies • Star formation: • sensitive to young stellar populations • Cold gas • Indicator of cold gas fraction in galaxies

  3. 1. Estimating cold gas fraction in galaxies • u-r, u-k as indicators Wei Zhang et al. 2009

  4. 1. Estimating cold gas fraction in galaxies • color plus surface brightness Wei Zhang et al. 2009

  5. HyperLeda + SCUSS • >100 HI galaxies from HyperLeda falling in the current SCUSS region • Expect to have >1000 eventually

  6. 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

  7. 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

  8. 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

  9. 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, …

  10. WISE preliminary release (Apr 14) • Overlapping area: 30<RA<50, 0<Dec<4 SCUSS Year 1

  11. WISE preliminary release (Apr 14) Wright et al. (2010) • Overlapping area: 30<RA<50, 0<Dec<4 SCUSS Year 1

  12. 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?

  13. 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

  14. 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

  15. Color-color diagram for star/galaxy separation 图片来自SCUSS项目书

  16. 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"

  17. Can we trust SDSS star/galaxy separation for faint sources? • SDSS: COMBO S11 field as a standard • 100% correct for r<19.5 galaxy star 图片来自SDSS/DR5网站

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