Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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DAZLE: Dark Ages “Z” Lyman

Explorer(visiting a Time when Galaxies are Young)

McMahon, Parry, Horton,Trentham, Bunker, Clarke, King, Mackay(Institute of Astronomy, Cambridge, UK)

Bland-Hawthorn(AAO, Australia)

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Experimental design issues

• How faint to go?

• How large a volume to search?

• How many galaxies or galactic sub-unit do we expect?

• The large uncertainties make this an important experiment

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Astrophysical principlesMinimum Flux limit• Previous surveys(e.g. Pritchett, Djorgovski) in the early 1990’s were

based on the simple paradigm of a monolithic collapse(Eggen, Lynden-Bell and Sandage, 1962) – expected star formation rates of 50-500 Msol yr-1

• Assume SFR detection limits more appropriate to a slowly disc or sub-galactic units in a halo– i.e. 1-3 Msol yr-1

0.5 - 1.0 10-17erg s-1 cm-2

Minimum Volume • search a comoving volume within which you expect to find the

progenitors of around 10 L* galaxies.– Local density 1.4±0.2 10-2 h50 Mpc-3 (e.g. Loveday etal, 1992)

minimum is 1000 Mpc3 [c.f. 10Mpc cube]

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Basic observational principles

• Target spectral regions where night sky is dark– between the intense OH line emission

• For z>5; i.e. >7295 angstroms– Optical; 7600-7700 z=5.25 - 5.33

– 8100-8250 z=5.66 - 5.79

– 9050-9300 z=6.44 - 6.65

• Sky background is 0.5-1.0 10-17erg cm-2 s-1 ang-1

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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An extremely luminous galaxy at z=5.74

Hu, McMahon, Cowie, 1999, ApJ, 522, L9

90” x 90”

500 x 500 h-1 kpc

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Technical/Observational Issues

• The sky is blue

• IR sky is bright

• 1-8micron IR sky brightness is dominated by intense, narrow OH airglow lines

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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DAZLE Baseline Design

• Rockwell Hawaii-II 20482 HgCdTe detector• Tunable Fabry-Perot filter from Queensgate

Instruments– R=2000; 150km/sec

– cooled to -20C

• Target telescope: Gemini South– f/16 collimator; 0.18”/pixel

– 6.2’x6.2’

• Sensitivity: 10-18 erg s-1 cm-2; 5in 15,000secs

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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Conclusions• In the last 5 years, the systematic detection of “normal” high

redshift galaxies has gone from z=1 to z=6 (mainly due to increased aperture of 10m Keck’s)

• we have already reached the silicon/optical limit

• future is the IR

• future is emission line based searches

• may require 1-5 nights to find a single z>7galaxy• 10-50 to detect 10 i.e.

• Terrestrial aperture is now available to allow such an experimental

N3N

Sackler DSI Trustees: 2001, Aug, 01 Richard McMahon (www.ast.cam.ac.uk)

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