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 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-m background

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

The SCUBA 850-m 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)

Number counts

5 sources > 2 mJy

Confusion analysis:

Euclidean counts

to S < 0.3 mJy

7000 deg-2 > 1 mJy

Optical counterparts

50K + =1.5 photometric z’s:

HDF 850.1 must have z > 3

HDF 850.1 continued

IRAM 1.3-mm position coincident with VLA source.

Between z=1 and z=2 galaxies, but inconsistent with either.

Downes et al. astro-ph/9907139

Structure in the background

Subtract 5 brightest point sources:

Residual structure from

source superposition:

correlation with known HDF starbursts?

Predicting sub-mm emission

Photometric redshifts + UV flux

” L1500

Dust-free starburst:

SFR = L1500 / 1021 W Hz-1

S850 / mJy = SFR / 20 h-2 Msun yr-1

Wide z range expected

Predicted sub-mm maps

z z

Significant cross-correlation over 1 < z < 6

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

Mean starburst emission

Detect non-zero flux at 0.1 mJy level:

0.14.4SFR visible

SFRhidden

cf. detection limits of 1-2 mJy for single pointings

cf. ratios > 100 for ULIRGs like 850.1

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

Clustering of the background

ln d ) θ ( ) ( ) θ ( 02 Jw

Measure clustering via dimensionless power spectrum

shot noise

true clustering

assume w = ()-0.8 :

find < 2 arcsec

reasonable if sub-mm galaxies have 1 < z < 6: Limber ” factor 3-4 reduction in w wrt Lyman-break galaxies

Summary

HDF starbursts emit at 850-m– statistical detections down to 0.1 mJy

– mean hidden : visible SFR is 4.5 : 1 The 850-m background is clustered

– consistent with shot noise

– limits background clustering to 0 < 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