Full Spectral Analysis of Galaxies - Are we there yet? Ben Panter, Edinburgh bdp@roe.ac.uk

Full Spectral Analysis of Galaxies - Are we there

yet? Ben Panter, Edinburgh

bdp@roe.ac.uk

Full Spectral Analysis?Emission lines give information on current star formation, but tell us nothing about the history.Good for redshifts too!

Continuum shape can reveal generics of populations, and perhaps a mass to light ratio.

Spectral features can help reveal the average metallicity when stars formed, and perhaps their mean age

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Pixels vs. Parameters

Models

Observations

Comparison Method3000 pixels

Need a clever way to perform this analysis for any non-trivial

parameterisation

How does MOPED solve this?

Short version:• Pick the pixels which tell you most about the parameters you

wish to extract from the data• Create a weighting vector, b, for each parameter which gives

a projection y (scalar) of the dataset x.

• ym=bm.x

• If model is good, then these y numbers encapsulate all the information about the parameters – the compression is lossless

• Can use these y values to determine likelihood of a parameter set, rather than x – hence computation time nparams not npixels

Long version: Heavens et al. 2000, Reichardt et al. 2001, Panter 2005.

Massively Optimized Parameter Estimation and Data Compression

MOPED2 (Mathis 06)

STARLIGHT (Cid Fernandez 05)

BLV (Nolan 06)MOPED (Panter 03)

VEPSA (Tojeiro 07) STECMAP (Ocvirk 03)

Not the only show in town…

So why bother?

z

High redshift sources• Limited to bright galaxies• Subject to IMF (high end)• Dependent on models• Uncertain dust correction

Low redshift sources• Subject to IMF (low end)• Dependence on models• Dust correction easier to manage• Many, many more galaxies...

z

Cosmic SFR to z~2 from z~0.1 sources (DR3)

Downsizing – Not Offset!

DownsizingDownsizing

Build up of Stellar Mass

Metallicity History Maps

Preliminary result, please do not redistribute

So are we there yet?

Lots of results that reassuringly agree with other indicators

Lots of information still to be untangled…

Looking at the modelsMissing Ingredients:• Alpha enhancement

– Models available

• Variable abundances– Infancy

• UV Continuum• IR Continuum

• Need to separate…

Models

Observations

Comparison Method

How can we differentiate features?• Two groups of high signal to noise

galaxies:– Telescope features fixed in observed frame,

Modelling features fixed in rest frame.– Very tight redshift range for clear observed

frame (W)– Wider range of redshift to smooth observed

frame (T)– Subtract residuals of W from T

Where do the models fail?

Average

Tight z

Wide z

T - W

Incorporating Alpha

Panter / Coelho in prep.

Preliminary result, please do not redistribute

How different are the models?

Modelling all the way - UV to IR

Nolan et al. 06

Future Surveys – what is needed?

Models

Observations

Comparison Method

• S/N in sloan is good, but other problems appear to dominate– Spectrophotometry

• Redshift range– Moderately higher

redshift helps a lot

• Database methods essential– GAVO

2SLAQ/DEEP2/GDDS/GOODS...

Higher redshift allows us to probe early epoch populations

High z SF from mid-z sources

Present data does not support reliable analysis (?)

Wish list for higher z FSA

• Resolution of ~ 1A• UV + Visible + IR with overlap• SDSS or better S/N • 10,000 galaxy spectra• z ~ 1• Accurate calibration of

spectrophotometry– Better than sloan?

Conclusions• Methods are in

place and tested• Models need

– Wider range at high res (observations!)

/ Var. Abundances– Uniform format

• Data needed– Moderately higher z– Spectrophotometry

(more important than numbers?)

Models

Observations

Comparison Method