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Structure in the sub-mm background towards the HDF

Structure in the sub-mm background towards the HDF. John Peacock & the UK sub-mm survey consortium. Novartis Institute, November 1999. Outline. Motivation for resolving the sub-mm background The SCUBA 850- m m map of the HDF Optical identifications of the S 850 > 2 mJy sources

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Structure in the sub-mm background towards the HDF

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  1. Structure in the sub-mm background towards the HDF John Peacock & the UK sub-mm survey consortium Novartis Institute, November 1999

  2. Outline • Motivation for resolving the sub-mm background • The SCUBA 850-mm map of the HDF • Optical identifications of the S850 > 2 mJy sources • Statistical detections of starbursts down to 0.1 mJy • Emission from z > 5 galaxies • Clustering of the 850-mm background

  3. Edinburgh: James Dunlop, Dave Hughes, Andy Lawrence, John Peacock • Imperial College: Andreas Efstathiou, Bob Mann, Seb Oliver, Michael Rowan-Robinson, Steve Serjeant • Cambridge: Andrew Blain, Malcolm Longair • UCL: Rob Ivison • JACH: Tim Jenness

  4. The SCUBA 850-mm HDF map • 50 hours integration • 100 arcsec radius • Beam: 14.5’’ FWHM • - 30’’ and 45’’ chop • Noise: 8’’ FWHM • - rms 0.45 mJy • - doubles at 90’’ • (divided out)

  5. Number counts • 5 sources > 2 mJy • Confusion analysis: • Euclidean counts • to S < 0.3 mJy • 7000 deg-2 > 1 mJy

  6. Optical counterparts 50K + b =1.5 photometric z’s: HDF 850.1 must have z > 3

  7. HDF 850.1 continued Downes et al. astro-ph/9907139 IRAM 1.3-mm position coincident with VLA source. Between z=1 and z=2 galaxies, but inconsistent with either.

  8. Structure in the background Subtract 5 brightest point sources: Residual structure from source superposition: correlation with known HDF starbursts?

  9. Predicting sub-mm emission Photometric redshifts + UV flux ” L1500 Wide z range expected Dust-free starburst: SFR = L1500 / 1021 W Hz-1 S850 / mJy = SFR / 20 h-2 Msun yr-1

  10. Predicted sub-mm maps Significant cross-correlation over 1 < z < 6 z<2.5 z>2.5

  11. Emission at extreme z NICMOS GTO data found 8 z > 5 candidates (including 4-473.0 at z=5.6): 2 close pairs match well with 1-mJy level peaks

  12. Mean starburst emission Detect non-zero flux at 0.1 mJy level: cf. detection limits of 1-2 mJy for single pointings cf. ratios > 100 for ULIRGs like 850.1

  13. Meaning of hidden SFR All star formation is ‘hidden’: never expect dust-free burst ‘hidden’ : ‘visible’ ratio depends on lifetime of high-mass stars and dust burnoff time Jimenez et al. models (astro-ph/9910279) predict 6:1 for Salpeter IMF Similar boost factor for SFR inferred by Pettini et al. from Balmer lines, but foreground screen is not the right model

  14. Clustering of the background Measure clustering via dimensionless power spectrum assume w = (q / q0)-0.8 : find q0 < 2 arcsec shot noise reasonable if sub-mm galaxies have 1 < z < 6: Limber ” factor 3-4 reduction in w wrt Lyman-break galaxies true clustering

  15. Summary • HDF starbursts emit at 850-mm • statistical detections down to 0.1 mJy • mean hidden : visible SFR is 4.5 : 1 • The 850-mm background is clustered • consistent with shot noise • limits background clustering to q0 < 2 arcsec • consistent with very broad redshift range contributing to background • Future issues • what is the upper redshift limit? • nature of HDF 850.1? • comparison with NICMOS

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