The 6dF Galaxy Survey - The Target Samples Will Saunders Anglo-Australian Observatory

UK Schmidt has huge AΩ, ~ AAT/2dF or SLOAN Galaxy source counts inversely with brightness => same number of accessible targets per unit time for given AΩ Schmidt has unique ability to cover whole sky So ideal for wide field, shallow samples, in particular new wavebands or techniques. And also ideal for peculiar velocities. 6dF coincides with first imaging and first NIR sky surveys - 2MASS, DENIS. Ending of photographic era allows large fraction of UKST time to go to 6dF Why 6dFGS

Instrumental parameters 1K x 1K chip - limited by existing spectrograph Focus 3-4 pixels fwhm over chip few hundred spectral resolution elements R>1000 resolution desirable for z-survey, imperative for D n -σ Coverage 3900A-7500A desired - z=0 H,K to z=0.1 Hα. => require 2 grating setups per field. 3 x 20min 600V 5-6A fwhm 3 x 10min 316R 9-12A fwhm 40 mins overhead between fields (changing field plate, flats and arcs, slewing, acquisition) => max 4-5 frames/night

Overall survey parameters: 4 year hard limit for UKST funding (to June 2005). Button size + plate scale => twice over coverage 2 x 17,000 deg 2 / 25 deg 2 =1400 fields 18 nights x 13 lunations x 4 years x 75% 6dFGS x 50% clear x 4 fields/night = 1400 fields 1400 fields x 130 targets/field = 180,000 spectra reserve 10,000 for z-survey reobservation, 10,000 for D n -σ reobservation => 160,000 observable targets.

The K s -selected sample 1 2MASS (2 Micron All-Sky Survey) covers whole sky in J,H,K s Very shallow, large pixels. Confusion limited in Plane. K s ideal place to study Large Scale Structure - Old stellar population - constant mass-to-light ratio Small external extinction Small internal extinction But need total magnitudes from low S/N data on extended objects.

K cor magnitudes 2MASS gives reliable isophotal magnitudes K 20 - comparable depth to 2dF for most galaxies. can easily determine average surface brightness within this isophote μ K20. 2MASS gives total magnitude K tot - noisy but OK at high latitude can use K 20, μ K20 + simple model to estimate total magnitude, compare with K tot Final estimator K cor = K 20 - min(1.5 e (1.25(μK20 -20)), 0.5) Robust to confusion noise Statistical error ~ 0.11 m Overall systematic error << 0.1 m Possible biases at 0.05 m level vs galaxy profile No extinction correction to the correction!

The K s -selected sample 2 Final selection: K cor < m extended sources |b|>10° δ < 0° A V < 5 m (protostellar sources) => 120,000 targets Early-type dominated Median redshift z~0.06 Tail to z~0.18

The peculiar velocity survey Whole new scale of peculiar velocity survey - can rewrite rules All spectra in principal good enough resolution and wavelength coverage for D n -σ Limited by S/N, ellipticity, linewidth, redshift, spectral type? Can reobserve suitable galaxies with marginally poor S/N (or alibi) Aim for S/N = 20/A at MgB Photometry from K s May want to set selection criteria at this meeting

Additional Samples 1 If covering whole sky, can include smaller samples along for the ride, especially if lower completeness is required (cf 2dFGRS/ 2dF quasar survey). Also, small numbers of additional targets in other bands can lead to large complete samples, useful for eg comparing clustering vs waveband. Samples agreed from early planning were: H,J-selected 2MASS galaxies to make complete samples ~100,000 in each: final limits Hcor < 13.0m, Jcor < 13.75m DENIS I,J -selected galaxies to Jkron < 13.85m, Ikron < 14.85m, for the 35% of of the sky for which DENIS data is reduced SUPERCOSMOS-selected galaxies with |b|>20 to rF<15.6m, bJ<16.75

Additional Samples 2 In addition, the AAO made a call for additional targets in late This led to a large number of smaller additional samples being included: All IRAS FSC galaxies with |b|>20, S/N > 6 ROSAT All Sky Survey quasars with bJ<18.5 m HI Parkes All Sky Survey galaxies with ambiguous optical identification 2MASS-selected red AGN candidates with J-K s > 2 Hamburg-ESO objective prism quasar candidates Quasar candidates from the VLA NVSS survey} Sources from the SUMSS survey with b J < 18.5 m 1000 galaxies to complete the Durham/UKST survey, 1- in-3 to b J < 17.5 m Galaxies in the Shapley supercluster to r F <16.0 m

ID sample weight total distinct unique observe 1 2m_K1275 8/ scos_R156 6/ scos_B1675 6/ fsc_b20r19 6/ RASS_final 6/ m_H1300 6/ m_J1375 6/ hipass4sig 6/ durukst 6/ shapley 6/ denisI1485 5/ denisJ1385 5/ df2magnid_b19r18 4/ hes 4/ nvss 4/ sumss 3/ totals