1. Comparison of different codes Patricia Sanchez-Blazquez
SELGIFS science case
Comparison of different codes
Patricia Sanchez-Blazquez

2. Chile-Japan forum Patagonia 2016

3. Archaeology Astro-Archaeology
“The scientific study of past human cultures by analyzing the material remains (sites and artifacts) that people left behind”
Astro-Archaeology
“The scientific study of past galaxies history by analyzing the material remains (old stars)”

4. Compare the ability of different codes to derive mean values of age and metallicity
The idea is to use three different codes: Paradise (Walcher et al. 2009) STARLIGHT (Cid Fernandes et al. 2005) STECKMAP (Ocvirk et al. 2006) We want to compare the methods and, therefore, we will use the same base in all cases, Bruzual & Charlot (2003)

5. S/N~40 per Å 5800Å)
Inversion algorithm
Mean values

6. Data: SELGIFS data challenge
We know the mean values of age and metallicity weighted with both, mass and light. This will allow us to test how well the different codes are performing.

7. Data: CALIFA galaxies (old, young, and intermediate)
NGC NGC NGC4185
voy a calcularles yo la cinematica…

8. Compare with a real galaxy (young, intermediate and old)
It’s going to be much easier that the codes reproduce the right answer with synthetic SFH than using real data. By comparing the results obtained with different codes we’ll get a better idea of the errors associated in the determination of mean age and metallicity values.
We will do the comparison in three different galaxies with three different stellar population properties: young, intermediate and old, to check how well the codes perform in the three different ranges.

9. Data
I will provide with individual spectrum, in fits format and with the associated error spectrum
neat.namegal.number_spaxel.lin.fits
neat.namegal.number_spaxele.lin.fits (error spectrum)

10. Procedure (1) Fit the spectra with a sum of SSP STARLIGHT STECKMAP
PARADISE
(2) Mask emission lines
(The cleaning is not perfect, so I would like to see how things change when the emission lines are masked)
(3) Obtain mean age, metallicity and extinction (weighting with both, L and M)
(4) Fit STECKMAP again using the continuum (to test how much of the variance is carried out by this feature)
THE MODELS in all cases will be Bruzual & Charlot (2003)

11. OUTPUT
You’ll provide with a mass-weighted and a luminosity-weighted value for each spectrum.
In the case of steckmap, we will also run the code using and not using the continuum.

12. outputs
When the code fit the continuum, the extinction will be also provide

13. Table to complete (Data vs Tools)
Code/gal
C-CS+
NGC6173
NGC873
NGC4185
STARLIGHT
Emission corrected
Emission
masked
Emission masked
Emission Corrected
STECKMAP
(without continuum)
STECKMAP (with continuum)
PARADISE

14. OUTPUT of the paper #1 comparison with synthetic spectra
Compare the outputs with the synthetic values (this will give us an idea of how well each code is performing in an idealized case)
When there are differences, we will identify where (e.g. young populations, when different burst are present, low or high metallicities, etc…)
How the results depend on the emission line correction
How the results depend on the continuum (this is very important in real data where flux calibration is usually not perfect and we have degeneracies between the stellar pop values and the extinction)

15. OUTPUT of the paper #1 comparison with real data
Compare the outputs for the three galaxies obtained with the three codes
Identify where the larger differences are found (low S/N, low or high ages, metallicities etc)
How the results depend on the emission line correction
How the results depend on fitting or not the continuum
CONCLUSIONS

16. Can we obtain an age-metallicity relation?
It would be very powerful if we can obtain the metallicity evolution of the galaxy by comparing the metallicity of the old and young populations. Is this possible? Do we obtain consistent answers with different codes? - Determine the metallicity of young and old populations with the different codes.