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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