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

6dF Galaxy Survey spectroscopic survey of 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey2

Early & Late Type Galaxies 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey3

Lick Indices Lick System: Å at ~9Å FWHM resolution common lines used in models above (measured many more) Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey4

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]) Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey5

What and Why Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey6 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.

Other’s Results Moore PhD early-type galaxies in Coma cluster – found ellipticals 2 Gyr older on average than lenticulars with similar metallicity Kuntschner sample 22 early-type galaxies in Fornax cluster found lenticulars younger and similar metallicity Jones et al no difference ages ellipticals and lenticulars Thomas & Kauffmann luminous ellipticals are the last to form in the hierarchical merger model Bernardi et al SDSS more massive galaxies are older Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey7

Data Reduction 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey8

My Sample galaxies observed once & 1105 galaxies observed twice 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+) Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey9

My Sample - Morphology Classified morphology using 2MASS NIR J, H & K and SuperCOSMOS Sky Survey optical B & R images 742 Large Sample - ellipticals 54%, lenticular 37%, spirals 9% 100 Good Sample - ellipticals 50%, lenticular 41%, spirals 9% Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey10

Velocity Dispersion & Morphology different morphology – different velocity dispersion distribution S0s – component from disk rotation at different alignments Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey11

Faber Jackson Relationship Faber-Jackson Relationship Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey12 red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals 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

Mgb vs. velocity dispersion black line slope –0.131 same as Colless et al (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 = (  0.034) x –0.044 (  0.077) rms 0.59 Mgb vs. Velocity Dispersion Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey13 red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals

Trager Data 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

Worthey Large 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 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 red dots - elliptical blue crosses - lenticular (S0) black distorted squares - spirals

Worthey Elliptical Ellipticals Only 50 points

Worthey Lenticular Lenticular (S0) 41 points no statistically significant difference

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

Thomas 5 Large 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

Ages for Good Sample 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey21

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) Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey22

Metallicity for Good Sample looks like lenticulars slightly more metal rich by eye – probably more effect of binning limits than real effect Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey23

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) Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey24

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 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey25

Age & [Fe/H] vs. K magnitude K luminosity – good indicator of stellar mass no pattern in age or metallicity with K Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey26

Comparison with Other’s Results disagree Thomas & Kauffmann 1999 and Bernardi et al – 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey27

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

Future Work 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 Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey29

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