The 6dF Galaxy Survey

Design and Goals

Matthew Colless

The 6dFGS WorkshopAAO, Sydney, 30-31 May 2002

Goals of the workshop

• To provide a clear view of the current state of play.

• To clarify the desired scientific outcomes.• To refine the survey plan and operations.• To enthuse participants in the survey!

• How? by sharing information and discussing plans regarding all aspects of the survey:– samples, observations, data reductions…– science, data releases, survey management…

Workshop program - Thursday

Parker

Saunders

Colless

Watson

Workshop program - Friday

Sadler

Stavely-Smit

h

Work

sh

op

p

art

icip

an

ts

The 6dF Galaxy Survey

• Three components to the survey… A NIR-selected redshift survey of the local universe. A peculiar velocity survey using Dn- distances. Redshift surveys of other ‘interesting’ source

samples.

• Strategic issues… – differentiation: what does the 6dFGS offer that is not

offered by the 2dFGRS, SDSS or other surveys?– impact: what survey characteristics are required in

order to maximize the scientific impact of each component?

– timeliness: how quickly must the survey be carried out in order to achieve its goals in a timely manner?

The main redshift survey - goals

• To measure the luminosity function of NIR-selected galaxies (i.e. the stellar mass function of collapsed structures) and its variation with local environment and spectral type.

• To map the local galaxy distribution (esp. close to the Galactic equator).

• To quantify the small- and large-scale clustering of galaxies weighted by stellar mass, and so constrain the scale-dependence of the biasing of the galaxies with respect to the dark matter.

• To measure the power spectrum of galaxy clustering on very large scales, comparable to the scales achieved by the 2dFGRS and SDSS.

• To construct a large, all-sky, volume-limited sample of early-type galaxies as the basis for the peculiar velocity survey.

• To provide a fundamental redshift catalogue for future work.

The 2dF Galaxy Redshift Survey

221,283 galaxy redshifts

5% sky coverage, z0.3

SDSS redshift survey

• Aim: ~106 galaxy z’s

• So far: ~200,000 z’s

• 25% sky coverage

• ugriz photometry

Advantages - sky coverage

2,000� 10,000 �

17,000 �

• Selection in the NIR (J,H,K) minimizes extinction effects of extinction - galaxies can be selected over |b|>10°.

• NIR luminosity is very closely correlated with total stellar mass, and so yields the stellar mass function.

log (Mstars/h-2M)

Advantages - NIR selection

• Optical selection is biased towards late-type, star-forming galaxies - NIR selection is thus better for the Dn- sample.

Galaxies with redshifts

Galaxies without redshifts

The 2MASS

Redshift Survey

N(K<12.2) = 116401

N(gals, z) = 32331

N(gals, no z) = 36474

LSS and cosmology from z-surveys

The peculiar velocity survey - goals

• To map in detail the density and peculiar velocity fields over half the local volume out to 15,000 km/s.

• To provide additional constraints on cosmological models, and better measurements of fundamental parameters, from statistics of these fields.

• To study the ages, metallicities and star-formation histories of early-type galaxies over a wide range of masses and environments.

The local density and velocity fields

PSCz predicted

velocity field (15,000

galaxies)

6dFGS observed velocity

field (15,000

galaxies)

102 peculiar velocities with infinite precision

102 peculiar velocities with 20% precision…

103 peculiar velocities with 10% precision…

103 peculiar velocities with 5% precision

• Problem: the cosmic + measurement variance on a single measured bulk motion on any scale is large - 90% c.i. is greater than model differences.

Bulk motions and cosmology

• Solution: measure rms bulk motions on a range of scales using surveys of large volumes.• Plots: show constraints on rms bulk motion at different scales for surveys with different numbers of groups of objects and precision of pec.vel.s for groups.

Additional targets, additional science

• To extend the scientific grasp of the survey and make the fullest use of this opportunity for whole-sky redshift surveys, the astronomical community was invited to supply additional targets of special interest.

• The AT programs include targets from the following sources:– 2MASS NIR sky survey – DENIS NIR sky survey– SuperCosmos galaxy catalogues– ROSAT All-Sky Survey (RASS)– HI Parkes Sky Survey (HIPASS)– IRAS Faint Source Catalogue (FSC)– NVSS and SUMSS radio surveys– Hamburg-ESO QSO survey

See talks to follow by:Koribalski, Drinkwater, Sadler, Wakamatsu, Cutri and Francis.

6dF positioner and spectrograph

Watson

Target samples

• 15 different samples• Merge target lists

and identify common objects

• Find objects with existing redshifts

• Set relative priorities

• Choose tiling of fields to optimize completeness and uniformity

Saunders

Target density and survey tiling

Campbell

Observed 6dFGS fields

Saunders

The redshift distribution

Predicted

Observed

Survey progress - 2dF and 6dF

6d

FGS

field

s

15001360

1200

900

600

300

0

Semester

01A 01B 02A 02B 03A 03B 04A 04B 05A 05B