Exploring the Stellar Populations of Early-Type Galaxies in the

6dF Galaxy Survey

Philip Lah

Honours Student h

Supervisors: Matthew Colless

Heath Jones

Outline

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 2

Exploring the

Stellar Populations ?? of

Early-Type Galaxies ??

in the

6dF Galaxy Survey ??

What is the 6dF Galaxy Survey?

one sentence answerg

A spectroscopic survey of nearby galaxies across the entire southern sky.

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 3

6dF Galaxy Survey• 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)

• also have 2MASS NIR J, H & K and SuperCOSMOS Sky Survey optical B & R magnitudes and images

Contour Plot of 6dF Galaxy Distribution

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 4

Good Spectrum

~ 44 S/N per Å

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 5

What are Early-Type Galaxies?

and the related question

What are Late-Type Galaxies?

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

Early & Late Type GalaxiesEarly-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 Survey 7

Why the interest in the stellar population?

The only significant contributor to the light from early-type galaxies is the starlight

g

Use stellar population models to measure the ages and metallicites of the galaxies

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 8

Stellar Population Models• models assume single burst of star formation – all stars

same age – similar to globular cluster

• input age of star formation & metallicity into the models – generate lists Lick indices, colours & magnitudes

3 stellar population models:

Worthey (1994) – standard model

Vazedekis (1996) – addresses issue of Horizontal Branch Stars

Thomas (2002) – includes non-solar abundances (various [/Fe], [/Ca] and [/N])

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 9

Lick Indices

Mgb

Lick Indices are a standardised way of measuring the equivalent width of a line

Mgb

Blue band pass

5142.625Å to 5161.375Å

Central bandpass

5160.125Å to 5192.625Å

Red Bandpass

5191.375Å to 5206.375Å

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 10

Lick Indices

• Lick indices defined in 1972 by Faber et al.

• wavelengths 4000-6200Å at ~8.6Å FWHM resolution

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 11

HG vs [MgFe]

• Age vs Metallicity Grid from Worthey model

• data from Stephen Moore thesis (2001) 87 galaxies in the Coma cluster

Moores MgFe

2

5335Fe5270FeFe

FeMgMgFe b

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 12

What I am doing?I am measuring various Lick indices in a sample of early-type galaxies from the 6dF Galaxy Survey.

Then I am analysing the results using the three stellar population models getting ages of star formation and metallicites for the galaxies.

What am I doing?

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 13

Why I am doing this?

To learn more about the formation of early-type galaxies in different environments.

Comparison of the properties of field and cluster galaxies: sddffff • expect field galaxies have same metallicity but are younger those in clusters (Kauffmann & Charlot 1998)

Comparison of elliptical and lenticular (S0) galaxies: soggggggme • previously found lenticulars younger than ellipticals fffffffffffff (Kuntschner 2000) & (Moore thesis 2001)

Comparison of the different stellar population models: sofffffffffff • new Thomas 2002 model with non-solar abundances to the older models

Why am I doing this?

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 14

My Work to Date

• using program indexf that measures Lick indices & gives errors

• using a Perl script to automate the process – measuring many different indices for many galaxies

• I have solved problems of lines redshifted into R spectrum & negative points in Lick bandpasses

• my current sample ~1100 galaxies – repeat observations with quality=4

used to calculate an error in z (z=0.0001596 v=47.8 kms-1)

comparing two values of a Lick index & the error measured by indexf from the repeat observations

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 15

My MgFe

My preliminary HG vs [MgFe]

Of ~1100 galaxies only 12 on plot

• No [OIII] emission

• High Signal to Noise

Not broadened to Lick FWHM ~8.5Å

Not velocity dispersion corrected

Not remove galaxies with H emission

Philip Lah, Honours StudentExploring the Stellar Populations of Early-Type Galaxies in the 6dF Galaxy Survey 16

The End