GAIA's View on the Metallicity of the MW galaxy.

Short research project at GAIA school held at Mexico City Dec-2013.

Transcript

1. GOG: Gaia Object Generator - Nbody/SHP galaxy data J. Fernández a,b , J. Garavito c, J. Muñoz d, P. Sánchez e a. Msc. Student at Universidad de los Andes (ULA), Mérida, Venezuela b. Centro de Investigaciones de Astronomía (CIDA), Mérida, Venezuela c. Msc. Student at Universidad de los Andes, Bogotá, Colombia d. Bsc. Student at Universidad Industrial de Santander (UIS), Bucaramanga, Colombia e. PhD. Student at Universidad Politécnica de Cataluña (UPC), Spain 12/11/2013 International GAIA School, D.F. México, México 1
2. Data: Test particle 12/11/2013 International GAIA School, D.F. México, México 2 N-particles with Gaia radial velocities GRVS <16.1 Galactocentric positions Size of data: 2.7 Gbytes , 21.8 M particles Absolute magnitude G< 16.5 G GRVS Xr Yr Zr Vxr Vyr Vzr Xobs Yobs Zobs Vxo Vyo Vzo Real date Date with errors of positions 12.2 M particles (56%) 100000 particles Filter 1 Filter 2 RR = (Xr 2 + Yr 2 ) 0.5 RObs = (XObs 2 + YObs 2 ) 0.5 Random selection
3. 12/11/2013 International GAIA School, D.F. México, México 3 A gamma distribution is used for each star with alpha (α) and beta (β) parameters calculated respect to the Sun placed at (x,y,z) = (-8.5, 0, 0) kpc. [Fe/H] = α * RR + β The Galactic metallicity gradient, W. Rolleston, S. Smartt, P. Dufton and R. Ryans. α = d[Fe/H] /dRGAL = -0.07 [Fe/H] SUN = 0= -0.07 * 8.5 + β β= 0.595 [Fe/H] = -0.07 * RR + 0.595 [Fe/H] without GAIA error (Real data) POSITION WITHOUT ERROR
4. 12/11/2013 International GAIA School, D.F. México, México 4 Given the real metallicities, we assign an error function (Gaiaerrors.f code) for each star. σError = 0.81192 - 0.12226 * G + 0.0056669 * G 2 (Liu et al. (2012), Antiche et al. 2013 ) The error is assigned assuming a Gaussian distribution. [Fe/H] with GAIA error (Real data) [Fe/H] Obs = Gaussian Deviation (Seed, [Fe/H] , σError ) Astrophysical parameters (Ap [1,2,3]): Teff, log(g), [Fe/H] GOG: Gaia Object Generator σError,i : GOG An approximation to simulate Gaia Products Teff Obs = f( σError,1 , Teff) log(g) Obs = f( σError,2 , log(g)) [Fe/H] Obs = f( σError,3 , [Fe/H]) POSITION WITHOUT ERRORS
5. 12/11/2013 International GAIA School, D.F. México, México 5 A gamma distribution is used for each star with alpha (α) and beta (β) parameters calculated respect to Sun placed at (x,y,z) = (-8.5, 0, 0) kpc. [Fe/H]’ Obs = -0.07 * RObs + 0.595 [Fe/H] without GAIA error (Data obs.) [Fe/H] with GAIA error (Data Obs.) [Fe/H]’ Obs-GAIA = Gaussian Deviation (Seed, [Fe/H]’ Obs , σError ) Given the metallicities EQUAL TO the real metallicities, the Sigma function (Gaiaerrors.f code) for each star does not change. And finally we assign the variance of a Gaussian distribution. POSITIONS WITH ERRORS
6. 12/11/2013 International GAIA School, D.F. México, México 6 [Fe/H] without GAIA errors (Real and Obs. data) COMPLETE DATA [Fe/H] with GAIA errors (Real data & Obs. data ) [Fe/H] = -0.07 * RR + 0.595 = 0 if RR > RSUN [Fe/H]’ Obs = -0.07 * RObs + 0.595 = 0 if RObs > RSUN For galactic radius larger than the sun´s radius, the metallicity is zero (x,y,z) = (- 8.5, 0, 0) kpc. [Fe/H] Obs = 0 if RR > RSUN [Fe/H]’ Obs-GAIA = 0 if RObs > RSUN
7. Negative slope (alpha (α=-0.07) and beta (β=0.595) ) 12/11/2013 International GAIA School, D.F. México, México 7
8. 12/11/2013 International GAIA School, D.F. México, México 8 Metallicities Distribution (Negative slope)
9. Negative (R< 8.5, 0) and constant slope (R>=8.5) 12/11/2013 International GAIA School, D.F. México, México 9
10. 12/11/2013 International GAIA School, D.F. México, México 10 Metallicity Distribution (negative and const. slope)
11. N-body / SPH simulation 12/11/2013 International GAIA School, D.F. México, México 11
12. N-body / SPH simulation Data: 12/11/2013 International GAIA School, D.F. México, México 12 We assume all the stars In the galaxy are Red Clumps With Mv=1.274 We select the stars Which are into GAIA’s Field v < 16.5. We also assume a simplified model of the extinction.
13. 12/11/2013 International GAIA School, D.F. México, México 13
14. 12/11/2013 International GAIA School, D.F. México, México 14 Number of RC stars in the GAIA’s field
15. 12/11/2013 International GAIA School, D.F. México, México 15 Metallicity distribution Distribution with GAIA errors Original distribution
16. 12/11/2013 International GAIA School, D.F. México, México 16 Metallicity gradient
17. 12/11/2013 International GAIA School, D.F. México, México 17 Metallicity Dispersion
18. 12/11/2013 International GAIA School, D.F. México, México 18
19. 12/11/2013 International GAIA School, D.F. México, México 19 GAIA errors computation
20. 12/11/2013 International GAIA School, D.F. México, México 20 Variation in metallicity as seen by GAIA
21. 12/11/2013 International GAIA School, D.F. México, México 21 Distance variation as seen by GAIA
22. 12/11/2013 International GAIA School, D.F. México, México 22 Conclusions The metallicity is truncated near the galactic centre probably due to the galactic bar. The metallicity dispersion tends to broaden at higher magnitudes, this is probably due to the population of the galactic centre ([Fe/H]>0 ) and anti-galactic centre ([Fe/H]). The observed data is consistent with the simulations of GOG. We found that as the galaxy evolves in the SPH/N-body code the slope of the metallicity decrease. We found no significant difference between the original metallicity and the one seen by GAIA. The metallicity does no change when errors are taking into account, but the dispersion increases when errors are taken into account.
23. 12/11/2013 International GAIA School, D.F. México, México 23 Acknowledgments: Francesca Figueras Octavio Valenzuela Daisuke Kawata Hoda Abedi Erika Antiche Santi Roca Ben Czaja