1. 6dFGS data quality: comparison of pipeline and IRAF redshifts Lesa Moore Macquarie University AAO 6dF Workshop 2005

2. Outline Spectral reduction and S/N Spectral reduction and S/N Wavelength calibration Wavelength calibration Cross-correlation redshift agreement Cross-correlation redshift agreement Quality measures – S/N, Q, r Quality measures – S/N, Q, r Repeatability Repeatability Final uncertainties Final uncertainties Based on comparisons between IRAF … and … 6dFDR/RUNZ processing Based on comparisons between IRAF … and … 6dFDR/RUNZ processing

3. Data Three fields studied (A, B and C) with repeat observations of the B and C fields: Three fields studied (A, B and C) with repeat observations of the B and C fields: A: Mar 16 2002, reflection gratings A: Mar 16 2002, reflection gratings B1: Sep 9 2002, reflection gratings B1: Sep 9 2002, reflection gratings B2: Sep 29 2003, VPH gratings B2: Sep 29 2003, VPH gratings C1: Sep 29 2002, VPH gratings C1: Sep 29 2002, VPH gratings C2: Sep 18 2003, VPH gratings C2: Sep 18 2003, VPH gratings

4. Method 6dFDR on separate V and R spectra 6dFDR on separate V and R spectra 6dFDR line lists 6dFDR line lists RUNZ on spliced spectra RUNZ on spliced spectra IRAF dofibers on separate V and R spectra IRAF dofibers on separate V and R spectra My own line lists My own line lists IRAF xcsao on spliced spectra IRAF xcsao on spliced spectra Batch mode processing, no heliocentric correction in either case Batch mode processing, no heliocentric correction in either case

5. Spectral Reduction 6dFDR reduction 6dFDR reduction Sometimes requires FIT rather than TRAM extraction (slower) Sometimes requires FIT rather than TRAM extraction (slower) Sometimes requires FLUX WEIGHTING option turned off Sometimes requires FLUX WEIGHTING option turned off

6. Signal to Noise FieldGratingS/NRemarks B1 Ref 316R ref 5.124 Average for 68 galaxies B2 VPH 425R VPH 12.119 B1 Ref 600V ref 7.313 Average for 69 galaxies B2 VPH 580V VPH 8.795 Software Field A, R data Field A, V data 6dFDR/splot3.062.34 Dofibers/splot3.172.22 6dFDR/RUNZ10.399.50 Dofibers/RUNZ10.248.89 Cross-processed Pipeline and IRAF reductions about equal VPH data superior to reflection grating data (figures from 6dFDR/RUNZ)

7. Line lists and  calibration Blue (V) data original line list had 14 lines Blue (V) data original line list had 14 lines 6dFDR typically locates 12 6dFDR typically locates 12 Software throws away 2 worst-fitting (leaves 10) Software throws away 2 worst-fitting (leaves 10) For red (R) data For red (R) data Line list omitted strong Ne line at 7032.41 Å Line list omitted strong Ne line at 7032.41 Å Arc spectra deficient of lines redward of 7500 Å (does not affect cross-correlation) Arc spectra deficient of lines redward of 7500 Å (does not affect cross-correlation) Found 2 nd order line from Hg at ~8092 Å Found 2 nd order line from Hg at ~8092 Å

8. Calibration Test Calibration Test Field C1 VPH reduced without sky subtraction Field C1 VPH reduced without sky subtraction Sky lines measured Sky lines measured 6dFDR results (±0.4 Å) equal to or superior to IRAF 6dFDR results (±0.4 Å) equal to or superior to IRAF

9. Cross-correlation An earlier version of RUNZ at Epping was applying the heliocentric correction incorrectly An earlier version of RUNZ at Epping was applying the heliocentric correction incorrectly RUNZ confused by noise in low S/N spectra RUNZ confused by noise in low S/N spectra Spliced spectra much more reliable than separate R and V Spliced spectra much more reliable than separate R and V

10. Redshift Agreement Agreement if Agreement if  z| ≤ 0.0005  z| ≤ 0.0005  cz| ≤ 150 km/s  cz| ≤ 150 km/s Overall agreement 81% for 294 galaxies in 3 fields Overall agreement 81% for 294 galaxies in 3 fields Could still both be wrong Could still both be wrong need to check by eye need to check by eye

11. Quality Measures Compared this redshift agreement with: Compared this redshift agreement with: S/N S/N RUNZ Q-ranking RUNZ Q-ranking Cross-correlation r-values Cross-correlation r-values as obtained from pipeline processing

12. S/N No strong correspondence between redshift agreement and S/N in separate R and V spectra No strong correspondence between redshift agreement and S/N in separate R and V spectra

13. Q-rankings Large scatter even with high Q Large scatter even with high Q Q-ranking012345Totals Disagrees6125218456 Agrees8313276118238 } 294

14. Q-rankings Around half the “disagrees” have Q of 3, 4, or 5 Around half the “disagrees” have Q of 3, 4, or 5 Q-ranking012345Totals Disagrees6125218456 Agrees8313276118238 } 294

15. Q-rankings Around half the “disagrees” have Q of 3, 4, or 5 Around half the “disagrees” have Q of 3, 4, or 5 Q=3 meant to imply 75% confidence (only 60% agree) Q=3 meant to imply 75% confidence (only 60% agree) Q-ranking012345Totals Disagrees6125218456 Agrees8313276118238 } 294

16. Cross-correlation r-value R-value is a much more useful indicator of redshift reliability than Q-ranking R-value is a much more useful indicator of redshift reliability than Q-ranking 84% of disagrees have r<6 84% of disagrees have r<6 27 of 33 disagrees with Q=3,4,5 have r<6 27 of 33 disagrees with Q=3,4,5 have r<6 72% of agrees have r>6 72% of agrees have r>6

17. SIMBAD-RUNZ difference vs. Q-ranking Q – rankings of 3, 4, 5 show large spread of error values (4, 14, 29 data points respectively) Q – rankings of 3, 4, 5 show large spread of error values (4, 14, 29 data points respectively) Have applied heliocentric correction this time Have applied heliocentric correction this time Note bias towards high-q results Note bias towards high-q results

18. SIMBAD-RUNZ difference vs. R-value Differences scale inversely with r-values Differences scale inversely with r-values St dev:  z = 0.00012,  km/s = 52 km/s (based on 34 galaxies whose redshift agreement meets criterion of  cz| ≤ 150 km/s) St dev:  z = 0.00012,  km/s = 52 km/s (based on 34 galaxies whose redshift agreement meets criterion of  cz| ≤ 150 km/s)

19. Repeatability End columns are large discrepancies End columns are large discrepancies All r>6 results lie within  z| ≤ 0.001 All r>6 results lie within  z| ≤ 0.001 Overall st.dev.   z = 0.00033 Overall st.dev.   z = 0.00033   km/s = 98 km/s   km/s = 98 km/s

20. Final uncertainties Notes Notes 1. Based on 0.4 Å at 4000 Å 1. Based on 0.4 Å at 4000 Å 2. Mean of “verr” from RUNZ (278 galaxies in total, 190 with r>6, possibly over-stated) 2. Mean of “verr” from RUNZ (278 galaxies in total, 190 with r>6, possibly over-stated) 3. 1/√2 * st. dev.(  z) of repeat 6dF observations (125 galaxies in total, 81 with r>6) 3. 1/√2 * st. dev.(  z) of repeat 6dF observations (125 galaxies in total, 81 with r>6) 4. Added in quadrature 4. Added in quadrature kms/s = z * 300,000 assumed in all cases kms/s = z * 300,000 assumed in all cases Source General Uncertainty Uncert. for r>6 redshifts ±km/s ±z±z±z±z ±z±z±z±z calibration 1 calibration 1300.0001300.0001 Cross-correlation 2 630.00021480.00016 Repeatability 3 690.00023390.00013 Total uncertainty 4 980.00033690.00023 The “6dF Galaxy Survey” Paper (2004) 82 km/s for Q = 3 46 km/s for Q = 4

21. Final uncertainties Notes Notes 1. Based on 0.4 Å at 4000 Å 1. Based on 0.4 Å at 4000 Å 2. Mean of “verr” from RUNZ (possibly over-stated) 2. Mean of “verr” from RUNZ (possibly over-stated) 3. 1/√2 * st. dev.(  z) 3. 1/√2 * st. dev.(  z) 4. Added in quadrature, final results rounded to one significant figure 4. Added in quadrature, final results rounded to one significant figure kms/s = z * 300,000 assumed in all cases kms/s = z * 300,000 assumed in all cases Source General Uncertainty Uncert. for r>6 redshifts ±km/s ±z±z±z±z ±z±z±z±z calibration 1 calibration 1300.0001300.0001 Cross-correlation 2 630.00021480.00016 Repeatability 3 690.00023390.00013 Total uncertainty 4 1000.0003700.0002 The “6dF Galaxy Survey” Paper (2004) 82 km/s for Q = 3 46 km/s for Q = 4

22. Summary S/N superior with VPH gratings S/N superior with VPH gratings RUNZ q-ranking not reliable indicator of z quality RUNZ q-ranking not reliable indicator of z quality Redshift agreement (IRAF-RUNZ) scales strongly with cross-correlation r-value Redshift agreement (IRAF-RUNZ) scales strongly with cross-correlation r-value Small uncertainty in calibration test Small uncertainty in calibration test Larger uncertainties in cross-correlation and repeatability tests Larger uncertainties in cross-correlation and repeatability tests Total uncertainties: Total uncertainties: 100 km/s general uncertainty 100 km/s general uncertainty 70 km/s uncertainty for r>6 redshifts 70 km/s uncertainty for r>6 redshifts

23. Thanks Macquarie University Macquarie University Anglo-Australian Observatory Anglo-Australian Observatory Wide-Field Astronomy Unit, Edinburgh Wide-Field Astronomy Unit, Edinburgh Supervisors: Quentin Parker (MU/AAO), Will Saunders (AAO) Supervisors: Quentin Parker (MU/AAO), Will Saunders (AAO) 6df Galaxy Survey Team (37 members) 6df Galaxy Survey Team (37 members) References References The 6dF Galaxy Survey: samples, observational techniques and the first data release, MNRAS, 355, 747-763 (2004) The 6dF Galaxy Survey: samples, observational techniques and the first data release, MNRAS, 355, 747-763 (2004) This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France