Evolved Stellar Populations as tracers of galaxy properties

Evolved Stellar Populations as tracers of galaxy properties

Maria-Rosa Cioni

Institute d’Astrophysique de Paris

Workshop: Optical and Infrared Wide-field Astronomy in Antartica

Friday 16th June 2006

Maria-Rosa Cioni

Institute d’Astrophysique de Paris

Workshop: Optical and Infrared Wide-field Astronomy in Antartica

Friday 16th June 2006

IntroductionIntroduction

To understand the history of formation and evolution of galaxies we need to understand the distribution of age, chemical abundance and kinematics of both the stars and gas.

The best laboratories for these studies are galaxies of the Local Group and in particular the Magellanic Clouds (nearby, known distance, low extinction, …interacting irregular galaxies).

Distinguish between cluster and field stars. A global picture of any LGG is lacking.

To understand the history of formation and evolution of galaxies we need to understand the distribution of age, chemical abundance and kinematics of both the stars and gas.

The best laboratories for these studies are galaxies of the Local Group and in particular the Magellanic Clouds (nearby, known distance, low extinction, …interacting irregular galaxies).

Distinguish between cluster and field stars. A global picture of any LGG is lacking.

Star formation historyhow is it measured?

Star formation historyhow is it measured?

Age Stars in a specific evolutionary phase. Fit of the main-sequence turn-off.

Metallicity Metallic lines from stars and nebula Ca II triplet Fit of isochrones/cluster tracks to a CMD C/M ratio

Kinematics Atomic and molecular lines

Age Stars in a specific evolutionary phase. Fit of the main-sequence turn-off.

Metallicity Metallic lines from stars and nebula Ca II triplet Fit of isochrones/cluster tracks to a CMD C/M ratio

Kinematics Atomic and molecular lines

Type of giant starsType of giant stars

Red giant branch (RGB) stars

All stars with 0.4-10 MSun become RGBs

Burn H in a shell Cool (bright in IR)

Red giant branch (RGB) stars

All stars with 0.4-10 MSun become RGBs

Burn H in a shell Cool (bright in IR)

Asymptotic giant branch (AGB) stars

All stars with 0.8-8 MSun become AGBs

Burn H and He alternatively in shells

Produce heavy elements (s-process)

Pulsate & Loose Mass Cool (brighter in IR)

Asymptotic giant branch (AGB) stars

All stars with 0.8-8 MSun become AGBs

Burn H and He alternatively in shells

Produce heavy elements (s-process)

Pulsate & Loose Mass Cool (brighter in IR)

AGBs are more extreme than RGBs.

Learning from AGB starsLearning from AGB stars

The number density The C/M ratio

The Ks-band magnitude

Low- and high-resolution spectra

The number density The C/M ratio

The Ks-band magnitude

Low- and high-resolution spectra

The structure The metallicity

[Fe/H] The star formation

history: mean-age and [Fe/H]

Dynamics and chemistry of different populations

The structure The metallicity

[Fe/H] The star formation

history: mean-age and [Fe/H]

Dynamics and chemistry of different populations

Selecting AGB starsSelecting AGB stars

AGB stars are brighter than the tip of the RGB and bluer than younger and foreground objects.

C-rich are redder than O-rich AGB stars Both criteria exclude upper-RGB stars.

AGB stars are brighter than the tip of the RGB and bluer than younger and foreground objects.

C-rich are redder than O-rich AGB stars Both criteria exclude upper-RGB stars.

O-rich: DENIS2MASS

C-rich:2MASSDENIS

Cioni, Habing & Israel 2000 Cioni et al. 2006

The structure of the LMCThe structure of the LMC

AGB stars are smoothly distributed across the galaxy.

They trace the orientation of the galaxy in the sky.

AGB stars are smoothly distributed across the galaxy.

They trace the orientation of the galaxy in the sky.

Van der Marel & Cioni 2001Cioni,Israel &Habing2000

…there are also sub-structures…there are also sub-structures

Discovery of an LMC star at 220 from the centre. Milky Way streams have been discovered using

RGB stars (photometry + kinematics). Sub-structures tracing the dynamical history exists

around M31 and other LG galaxies. Many galaxies have also extended halos. What is the mechanism that formed giant LG

galaxies like the MW and M31? Accreting satellites? (follow the streams…) (Chemistry) but not those surviving…

Discovery of an LMC star at 220 from the centre. Milky Way streams have been discovered using

RGB stars (photometry + kinematics). Sub-structures tracing the dynamical history exists

around M31 and other LG galaxies. Many galaxies have also extended halos. What is the mechanism that formed giant LG

galaxies like the MW and M31? Accreting satellites? (follow the streams…) (Chemistry) but not those surviving…

Calibrating C/M vs [Fe/H]Calibrating C/M vs [Fe/H]

Observational correlatation: solar neighbourhood, Magellanic Clouds and Baade’s Window

Theoretical correlation: in a metal poor environment

- the giant branch shifts to warmer T (less M giants),

- less C atoms are needed to form C stars.

Observational correlatation: solar neighbourhood, Magellanic Clouds and Baade’s Window

Theoretical correlation: in a metal poor environment

- the giant branch shifts to warmer T (less M giants),

- less C atoms are needed to form C stars.

Battinelli & Demers 2005

LMCMetallicity

LMCMetallicity C/M ratio map confirms

a metallcity gradient across the LMC.

[Fe/H]=0.75 dex.

Metal-weak/metal rich ratio estimated from the location of RGB stars in the near-IR diagram vs. distance.

C/M ratio map confirms a metallcity gradient across the LMC.

[Fe/H]=0.75 dex.

Metal-weak/metal rich ratio estimated from the location of RGB stars in the near-IR diagram vs. distance.

Alves 2004

Cioni & Habing 2003

M33 M33

C/M ratio map

C/M ratio as a function of distance: - the galaxy is surrounded by metal poor material - at large radii flattening of rotation induces gas outflows (higher Z).

C/M ratio map

C/M ratio as a function of distance: - the galaxy is surrounded by metal poor material - at large radii flattening of rotation induces gas outflows (higher Z).

Rowe et al. 2005

Cioni, et al., in prep.

Magellanic Clouds SFH statusMagellanic Clouds SFH status LMC

The dominant stellar population is >2.5 Gyr.

The bar is 1-3 Gyr old but stars of 4-8 Gyr are also present.

Bursts are associted to the interaction with SMC and MW.

SF propagates in the bar from SE to SW.

LMC The dominant stellar

population is >2.5 Gyr. The bar is 1-3 Gyr old

but stars of 4-8 Gyr are also present.

Bursts are associted to the interaction with SMC and MW.

SF propagates in the bar from SE to SW.

SMC The average stellar

population is older and more metal poor.

Old stars occupy outer regions and young stars the wing.

Half of the stars are >8.4 Gyr; recent bursts; intermediate-age ring (Harris & Zaritsky 2004)

SMC The average stellar

population is older and more metal poor.

Old stars occupy outer regions and young stars the wing.

Half of the stars are >8.4 Gyr; recent bursts; intermediate-age ring (Harris & Zaritsky 2004)

Magellanic Clouds dataMagellanic Clouds data

The MCs are an example of interacting Irr galaxies like others in the Universe.

Previous results were obtained from spatially limited regions in the outer/inner disk and in the bar (i.e. using HST).

No global picture! Wide-field observations:

Near-IR DENIS & 2MASS (one step further)

The MCs are an example of interacting Irr galaxies like others in the Universe.

Previous results were obtained from spatially limited regions in the outer/inner disk and in the bar (i.e. using HST).

No global picture! Wide-field observations:

Near-IR DENIS & 2MASS (one step further)

Ks-band methodKs-band method

The magnitude distribution of C-rich and O-rich AGB stars as a function of postion in the galaxy is interpreted using stellar evolutionary models.

The selection criteria is homogeneous.

The magnitude distribution of C-rich and O-rich AGB stars as a function of postion in the galaxy is interpreted using stellar evolutionary models.

The selection criteria is homogeneous.

Cioni et al. 2006

Constructing the theoretical Ks-band AGB distribution

Constructing the theoretical Ks-band AGB 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 for massive stars Girardi et al. 2000 for low- and intermediate-mass stars Marigo et al. 1999 for thermal pulsing AGB stars

Using bolometric tables to derive magnitudes and including photometric errors.

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 for massive stars Girardi et al. 2000 for low- and intermediate-mass stars Marigo et al. 1999 for thermal pulsing AGB stars

Using bolometric tables to derive magnitudes and including photometric errors.

LMC spatial distribution of metallicity, mean-age and chi2

LMC spatial distribution of metallicity, mean-age and chi2

Metallicity is high towards the MW and low towards the SMC. Average is Z=0.006.

Average (all stars) mean-age is 5-6 Gyr. The resolution is 2-5 deg2 (size of sectors).

Metallicity is high towards the MW and low towards the SMC. Average is Z=0.006.

Average (all stars) mean-age is 5-6 Gyr. The resolution is 2-5 deg2 (size of sectors).

P>80%

LMC: how well the C/M ratio indicates metallicity?

LMC: how well the C/M ratio indicates metallicity?

These maps are corrected for the LMC orientation. East is younger and metal richer than West. The C/M ratio is a robust indicator of metallicity. Regions of low probability:

These maps are corrected for the LMC orientation. East is younger and metal richer than West. The C/M ratio is a robust indicator of metallicity. Regions of low probability:

Z ageC/M

SMCMetallicity distribution as a

function of mean-age

SMCMetallicity distribution as a

function of mean-age

The region of high metallicity moves clockwise along a ring with increasing mean-age of the underlying stellar population….!

2 Gyr 3.9 Gyr 6.3 Gyr 8.7 Gyr

10.6 Gyr

Other Local Group galaxiesOther Local Group galaxies M33: bright Spiral

Nucleus, disk, halo and no bulge… Many giants and abundance gradients.

NGC 6822: isolated magellanic type Irr Bar embedded in a large HI envelope and in a

large decouple C star spheroid. Present low SFR. Contains RR Lyrae & LPVs.

SagDIG: distant dwarf Irr Metal poor galaxy with signs of extended SF.

M33: bright Spiral Nucleus, disk, halo and no bulge… Many giants and abundance gradients.

NGC 6822: isolated magellanic type Irr Bar embedded in a large HI envelope and in a

large decouple C star spheroid. Present low SFR. Contains RR Lyrae & LPVs.

SagDIG: distant dwarf Irr Metal poor galaxy with signs of extended SF.

M33metallicity, mean-age & chi2

M33metallicity, mean-age & chi2

In the centre the metallicity is low (Z<0.001) compared to a ring around it (Z>0.002).

The stellar population is on average 7-8 Gyr old. Map resolution of 3-13 arcmin2. No correction for rotation yet.

In the centre the metallicity is low (Z<0.001) compared to a ring around it (Z>0.002).

The stellar population is on average 7-8 Gyr old. Map resolution of 3-13 arcmin2. No correction for rotation yet.

P>99%

Cioni, Irwin, Ferguson et al., in prep.

NGC 6822metallicity, mean-age & chi2

Cioni, Stock, Girardi, Marigo & Habing, in prep.

NGC 6822metallicity, mean-age & chi2

Cioni, Stock, Girardi, Marigo & Habing, in prep.

The population is on average 8.5 Gyr old. The metallicity is high SE (Z>0.008), spiraling

inwards and low (Z<0.005) in other places. Map resolution of 19-164 arcmin2. No correction for orientation yet.

The population is on average 8.5 Gyr old. The metallicity is high SE (Z>0.008), spiraling

inwards and low (Z<0.005) in other places. Map resolution of 19-164 arcmin2. No correction for orientation yet.

P>90%

SagDIGSagDIG

C stars are not many but their number trace sufficiently well the Ks-band distribution.

The population is on average young (4 Gyr) and metal poor (Z=0.0005 at least).

C stars are not many but their number trace sufficiently well the Ks-band distribution.

The population is on average young (4 Gyr) and metal poor (Z=0.0005 at least).

Z=0.0005 filled trianglesZ=0.001 empty trianglesZ=0.004 filled squaresZ=0.008 filled squares

Gullieuszik, Rejkuba, Cioni, Held, in prep.

SFH: conclusionsSFH: conclusions

Interpreting the Ks-band distribution of AGB stars allows to estimate variations in mean-age and metallicity across stellar populations.

Modest but complete samples produce equally satisfactorily results.

This technique can be applied to more distant systems resolved into stars.

Interpreting the Ks-band distribution of AGB stars allows to estimate variations in mean-age and metallicity across stellar populations.

Modest but complete samples produce equally satisfactorily results.

This technique can be applied to more distant systems resolved into stars.

What is missing?What is missing?

Absolute values of age and Z Kinematics and detailed chemistry Effect of interaction (intrinsic versus

extrinsic star formation) 3D picture VISTA and AAOmega are promising

instruments to complete the picture of nearby galaxies and in particular of the Magellanic Cloud system.

Absolute values of age and Z Kinematics and detailed chemistry Effect of interaction (intrinsic versus

extrinsic star formation) 3D picture VISTA and AAOmega are promising

instruments to complete the picture of nearby galaxies and in particular of the Magellanic Cloud system.

A pre-selected VISTA Public Survey proposal - VMC

A pre-selected VISTA Public Survey proposal - VMC

PI: Cioni Area: LMC + SMC + Bridge

+ Stream (a few tiles) Filters: YJKs Gross Time:

21h-Ks and 4h-Y&J / tile Aims:

- Spatially resolved SFH - 3D picture

PI: Cioni Area: LMC + SMC + Bridge

+ Stream (a few tiles) Filters: YJKs Gross Time:

21h-Ks and 4h-Y&J / tile Aims:

- Spatially resolved SFH - 3D picture

VMC

2MASS

VMC survey: VISTA Magellanic Clouds survey

10

10

Variability issuesVariability issues

Deep Ks-band observations require multiple exposure that if appropriately placed may provide period and amplitude of variable stars: RR Lyrae, Cepheids, LPVs.

Advantages: Period-magnitude relations involving Ks have a

much smaller scatter: can be used for 3D pics. Combining variations in different bands

approaches the study of bolometric variations.

Deep Ks-band observations require multiple exposure that if appropriately placed may provide period and amplitude of variable stars: RR Lyrae, Cepheids, LPVs.

Advantages: Period-magnitude relations involving Ks have a

much smaller scatter: can be used for 3D pics. Combining variations in different bands

approaches the study of bolometric variations.

Dome C observations of Magellanic Cloud giantsDome C observations of Magellanic Cloud giants

Favourable RA and DEC. Large and diverse AGB sample. Mass-loss vs. metallicity/age/location Mid-IR (>Ks) monitoring (bolometric

variation/evolution) Polarimetry probing envelope shapes High spatial resolution (deeper & sharper images) Wide-area (statistics) 2.4m telescope is better (Ks saturation)

Favourable RA and DEC. Large and diverse AGB sample. Mass-loss vs. metallicity/age/location Mid-IR (>Ks) monitoring (bolometric

variation/evolution) Polarimetry probing envelope shapes High spatial resolution (deeper & sharper images) Wide-area (statistics) 2.4m telescope is better (Ks saturation)

How far can AGB stars be observed from Antarctica?How far can AGB stars be observed from Antarctica?

Ks=25.8 allow us to well detect AGB stars in the Fornax cluster of galaxies if they are sufficiently isolated.

A resolution of 0.2”/pix allow us to characterise the stellar population of galaxies within 5 Mpc (including Cen A)

Monitoring is clearly an advantage vs. larger telescopes observing plans.

Ks=25.8 allow us to well detect AGB stars in the Fornax cluster of galaxies if they are sufficiently isolated.

A resolution of 0.2”/pix allow us to characterise the stellar population of galaxies within 5 Mpc (including Cen A)

Monitoring is clearly an advantage vs. larger telescopes observing plans.