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Maria-Rosa Cioni - University of Edinburgh / University of Hertfordshire

The Magellanic Clouds as a template for the study of stellar populations and galaxy interactions
CSIRO (Australia), 16-17 July 2007


Introduction
MW LMC

?

Substructure formation: dark matter halos
(Diemand et al. 2006)

Galaxies are embedded in dark matter halos Galaxies are made of luminous matter (stars & gas) Different generation of stars change galaxy chemistry Galaxies, stars and gas move


Questions & answers ?
Do we understand the full picture? The full picture is complex! Can the Magellanic Clouds help? Metal poor - early Universe known distance - high details less reddening - sharp & deep Interacting irregular galaxies - many the largest MW satellites - neighbours extended history!


A "biased" view of the MCs (highlights)
Near-IR Upper RGB & AGB stars Number density - morphology & structure C/M ratio - metallicity (Fe/H] Ks mag - variation of mean age & metallicity Opt. Spectra - dynamics & chemistry


The structure of the LMC
AGB stars are smoothly distributed and trace the orientation of the galaxy in the sky


Cioni, Habing & Israel 2000 van der Marel & Cioni 2001


Ks-method

The SFR derived from localized regions does not produce a good fit across the whole galaxy!

O-rich AGB C-rich AGB RGB & others

Cioni et al. 2006

The magnitude distribution of C-rich and O-rich AGB stars as a function of position in the galaxy is interpreted using stellar evolutionary models spanning a range of SFRs and metallicities


The best fit model to each histogram corresponds to the best mean metallicity and age of the entire stellar population at that location The absolute value of age and metallicity is model dependent The range of SFRs and Zs chosen shows spatially relative differences but is not exhaustive


Theoretical Ks distribution
TRILEGAL code: simulates stars according to a SFR, AMR and IMF L, Teff, g are interpolated among stellar evolutionary tracks from:

Bertelli et al. (1994) - massive stars Girardi et al. (2000) - low & intermediate mass stars Marigo et al. (1999) - thermal pulsing AGB stars

Using bolometric tables to derive magnitudes and include photometric errors


Large Magellanic Cloud
mean metallicity, C/M & mean age

The population is younger in the E than in the W The bar has a composition stellar population The C/M ratio is a robust indicator of metallicity Maps are corrected for the LMC orientation Regions poorly constrained:


(Cioni et al. 2006)

Small Magellanic Cloud
Snap shots of the average metallicity (iron) across the galaxy The highest concentration moves with age
2 Gyr 3.9 Gyr 6.3 Gyr 8.7 Gyr 10.6 Gyr


A ring-like feature?

Colours equal different metallicity: Z = 0.008 (red), 0.004 (green) and 0.001 (blue)

Harris & Zaritsky 2004: inward propagation of star formation remnant of a gas rich merger


In-homogeneities as records of a clumpy
Dynamical simulations

fossil past

Distribution of stars originating from different stellar clumps Each clump has an age and a metallicity Clumps of <107 Msun dissolve to form field stars

(Bekki & Cioni, 2007)


What is missing?
Absolute values of age and metallicity Kinematics and detailed chemistry Effects of interactions (intrinsic versus extrinsic star formation) 3D picture Link between gas & stars New instruments & models should allow us to "complete" / "complicate" the picture of the Magellanic system


5%

5%

5%

20%

40%

10%

5%

5%

5%

The VISTA Public Survey VISTA of the Magellanic Clouds Magellanic Clouds (LMC+SMC+Bridge+Stream)
Co-Is = K. Bekki, G. Clementini, W. de Blok, C. Evans, Bekki, R. de Grijs, B. Gibson, L. Girardi, M. Groenewegen, V. Ivanov, P. Leisy, M. Marconi, C. Mastropietro, B. Moore, T. Naylor, Mastropietro, J. Oliveira, V. Ripepi, J. van Loon, M. Wilkinson, P. Wood

PI = M. Cioni

VISTA is a new and the best IR telescope of this time!


Arnaboldi et al. 2007, The Messenger 127

VISTA Public Surveys
Ultra- ; Dunlop, Frax, Fynbo, Le Fevre Hemisphere Survey (VHS); McMahon Deep Extragalactic Observations Survey (VIDEO); Jarvis Variables in the Via Lactea (VVV); Minniti Kilo Degree Galaxy Survey (VIKING); Sutherland Near infrared survey of the Magellanic System (VMC); Cioni


Area of VISTA Public Surveys


VISTA telescope & camera
VISTA tile VIRACAM detector plane 4m telescope @ Paranal 16 IR detectors 0.84-2.5 micron ZYJHKs & 1.18 NB 0.339"/pix resolution 0.51" instrument PSF 75% time for Public Surveys A tile covers Each pixel is least twice 1.65 deg2 covered at

Detectors distance 95% in X and 47.5% in Y; 6 pointings fill a tile


VST- optical fields

VMC area
Filters = Y, J, Ks

VISTA tile ~ 1.6 sq.deg.

Time = 180 nights

ё 1,500,000

LMC

Bridge

Stream

SMC

VMC (2008-2013) will produce a unique infrared data base to fully comprehend the Magellanic System


VMC observing strategy
Total area = 184 deg2 Seeing = 0.6", 0.8", 1.0" Sensitivity @ S/N = 10
1 2 x x YJKs YJ and same 11 x 116-LMC, 45-SMC, 20-Bridge, 3-Stream

Integration ~80% efficient: Mid-term goal:

Y = 21.9, J = 21.4, Ks = 20.3 night Ks - same semester

One epoch @ 3 filters for each tile More epochs on a given Magellanic component


VMC science goals
Spatially resolved SFH & metallicity evolution 3D geometry of the system & age dependency (empirical and theoretical) Substructures: new clusters and streams
Simulation
2MASS Ks=14.3 10s

VMC Ks=20.3 10s


Star formation history

Recovered SFH for 0.1-12 Gyr constant SFR; errors similar to expectations Chi2 of recovered minus observed SFH for different tests vs survey depth


Geometry indicators
The red clump luminosity The periodluminosity relation for RR Lyrae and Cepheids Standard candles in clusters

Log(P) vs Ks relation for RR Lyrae stars in the Reticulum


Ancillary science
Distance to the LMC - reduce the uncertainty via IR tracers Obscured massive stars; pre-MS 1.5 Msun unreddened; PNe & HII regions w/spectra Proper motion w/2MASS (~15 years) Follow-up!


Complementary surveys
EROS-II (MCs, wide coverage) SIRIUS & deep 2MASS (Ks~16) SAGE & S3MC MOSAIC (Deep outer MCs) Akari (all sky + LMC) STEP @ VST (Bridge var. & SMC) GAIA recent recent ongoing ongoing ongoing planned planned


Conclusion
The next 5 years will explain the Magellanic System Prior to GAIA, JWST and ALMA we will need to exploit VISTA These surveys will provide high and unique quality data for science and training of new generations