Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey

1. Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah Honours Student h Supervisors: Matthew Colless Heath Jones

2. 6dF Galaxy Survey • spectroscopic surveyof nearby galaxies across the southern sky • targets are near infrared selected (K band) • started mid 2001; to end mid 2005; the first public data release was Dec 2002 • ~13,000 V & R spectra with redshifts; peak z~0.05 (~200 Mpc) Contour Plot of 6dF Galaxy Distribution Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 2

3. Early-Type • elliptical & lenticular (S0) • no evidence of HII emission regions: no H or [OIII] emission & have Habsorption • dominated by old stars with no recent star formation • Late-Type • spiral & irregular • evidence of HII emission regions: H, [OIII] & H emission • mixture old & young stars, ongoing star formation Early & Late Type Galaxies Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 3

4. Lick Indices • Lick System: 4000-6200Å at ~9Å FWHM resolution • common lines used in models above (measured many more) Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 4

5. Stellar Population Models • input age of star formation, metallicity & IMF • generate lists Lick indices, colours • problem of age / metallicity degeneracy (increase in age same effect as decrease metallicity) • stellar population models: • Worthey (1994) – standard model in literature • Thomas (2003) – includes non-solar abundances (various models with different [/Fe]) Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 5

6. What am I doing? I am studying properties of the stellar population of early-type galaxies using the stellar population models. In particularly looking for any differences between lenticulars (S0s) and ellipticals. Also looking for any relationship between luminosity and age or metallicity. Why am I doing this? This work should give clues on how galaxies formed. Help discriminate between the hierarchal merger and monolithic collapse formation models. What and Why Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 6

7. Other’s Results • Moore PhD 2001 - 87 early-type galaxies in Coma cluster – found ellipticals 2 Gyr older on average than lenticulars with similar metallicity • Kuntschner 2000 - sample 22 early-type galaxies in Fornax cluster found lenticulars younger and similar metallicity • Jones et al. 1999 no difference ages ellipticals and lenticulars • Thomas & Kauffmann 1999 - luminous ellipticals are the last to form in the hierarchical merger model • Bernardi et al. 2003 - SDSS more massive galaxies are older Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 7

8. measure Lick indices with a program indexf • problems of lines redshifted into R spectrum & negative points in Lick bandpasses • measure S/N & redshift error using repeated observations • broaden to Lick resolution & continuum divide spectrum • measure velocity dispersion & correct Lick indices • measure H (& nearby [NII] doublet) • calibrate data against other observations • automate all these processes Data Reduction Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 8

9. 10054 galaxies observed once & 1105 galaxies observed twice 11159 observed once & higher S/N of repeated observations 8198 with “good” velocity dispersions (K and G star templates) 4538 my early-type cut (non-starforming) => H > 0.7 Å – 2 and [OIII]4959 > 0.8 Å– 2 and [OIII]5007 > –0.6 Å– 2 742 Large Sample –cut on error / S/N - HG and [MgFe]  <0.30 (S/N ~20+) 100 Good Sample HG and [MgFe]  <0.15 (S/N ~40+) My Sample Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 9

10. Classified morphology using 2MASS NIRJ, H& Kand SuperCOSMOS Sky Survey opticalB&Rimages 742 Large Sample - ellipticals 54%, lenticular 37%, spirals 9% 100 Good Sample - ellipticals 50%, lenticular 41%, spirals 9% My Sample - Morphology Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 10

11. different morphology – different velocity dispersion distribution • S0s – component from disk rotation at different alignments Velocity Dispersion & Morphology Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 11

12. Faber-Jackson Relationship Faber Jackson Relationship • L  4 (log slope –4) • black line slope -4 • red line ellipticals • y = -4.9 (0.7) x –14 (2) • rms 0.40 • blue line lenticular (S0) • y = -2.4 (1.5) x –19 (3) • rms 0.59 red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 12

13. Mgb vs. Velocity Dispersion Mgb vs. velocity dispersion • black line slope –0.131 same as Colless et al. 1998 (offset different due to different calibration) • red line ellipticals • y = 0.22 (0.04) x –0.32 (0.1) rms 0.40 • blue line lenticular (S0) • y = 0.099 (0.034) x –0.044 (0.077) rms 0.59 red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 13

14. 381 galaxies & 38 globular clusters – re-observations of objects used in defining Lick indices (absorption line objects) • used to calibrate stellar population models • used to calibrate my data – so that have similar distribution – add offset Trager Data

15. Large Sample (742 galaxies) • Error smaller than Trager data rms error 0.20 Å • my results concentrate on Good Sample of 100 galaxies red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals Worthey Large

16. red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals Worthey Good • Good Sample (100 galaxies) • note: lower HG points are removed by quality cut – probably problems with Lick index continuum fit • rms Error 0.12 Å

17. Worthey Elliptical Ellipticals Only 50 points

18. Worthey Lenticular • Lenticular (S0) • 41 points • no statistically significant difference

19. red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals • Good Sample (100) • [/Fe] = 0.0 • Solar abundance Thomas 0 Large

20. Good Sample (100) • [/Fe] = 0.5 • shifts up and to left – more shift in HG • my data fits on both grids • haven’t looked at ages & metallicities from Thomas grid red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals Thomas 5 Large

21. x-axis in log(age) – if plot linear age - fraction is relative constant • difference with Large Sample – S0’s drop off in age in last bin Ages for Good Sample Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 21

22. Cumulative Distribution of Ages • red line ellipticals • blue line lenticulars (S0) • K-S Statistic (Kolmogorov-Smirnov) • probability data drawn from same distribution • Lenticular & Elliptical Ages sample probability 0.92 (Large Sample 0.135) Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 22

23. looks like lenticulars slightly more metal rich by eye – probably more effect of binning limits than real effect Metallicity for Good Sample Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 23

24. Cumulative Distribution of [Fe/H] • red ellipticals line • blue lenticulars (S0) line • Lenticular & Elliptical Metallicities taken from same sample Probability 0.63 (from Large Sample 0.037) Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 24

25. Comparison with Other’s Results • no variation in metallicity agrees with Moore PhD 2001, Kuntschner 2000 and Jones 1999 • I detect no age variation unlike Moore and Kuntschner but agrees with Jones et al. 1999 • reason for difference: • - my sample not from one rich cluster or only from rich clusters (includes field galaxies) (my data is a magnitude limited sample) • - large error bars hide any small pattern Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 25

26. K luminosity – good indicator of stellar mass • no pattern in age or metallicity with K Age & [Fe/H] vs. K magnitude Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 26

27. Comparison with Other’s Results • disagree Thomas & Kauffmann 1999 and Bernardi et al. 2003 –no pattern between age and luminosity / mass • reason for difference: • - my sample over small magnitude range (~2 mag) for bright galaxies (magnitude limited sample) • - size of my errors smear out any correlation • - there may not be any correlation Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 27

28. 6dF Galaxy Survey Slices Field vs. Cluster z limit 0.05 Cluster sizes rectangles 300 kms-1 by 150 kms-1

29. do a field vs. cluster comparison • use other stellar population models and other indices (like H and H) for ages and metallicities measurements • use other indices that are more sensitive to [/Fe] to examine any differences using Thomas model • I have H and [NII] equivalent widths measured – an analysis of these interesting • do a direct comparison of the stellar population model spectra and 6dFGS spectra – go beyond Lick indices • another 6dF Galaxy Survey data release in Dec 2003 – more data with new gratings on 6dF spectrograph with higher S/N – the eventually completed survey will have ~13 times more data Future Work Exploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey Philip Lah, Honours Student 29

30. The End The End