Infrared sources in the galaxies of the Local Group

1
Infrared sources in the galaxies of the Local
Group
Based on Spitzer Space Telescope observations

• Mikako Matsuura (University College London)

M.J. Barlow, P.A., G.C. Sloan, A.A. Zijlstra,
P.A. Whitelock, P. R. Wood, M.-R.L. Cioni, M.A.T.
Groenewegen, K. Volk, J. Bernard-Salas, F.
Kemper, T. Kodama, E. Lagadec, M. Meixner, S.
Srinivasan, C. Szyszka, J.Th. van Loon
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Asymptotic Giant Branch (AGB) stars

• Bright mid-infrared point sources AGB stars
• Asymptotic Giant Branch (AGB) stars
• One of the remaining problem in stellar
  evolutions
• Mass loss from AGB stars
• Mass of the stars reduces in time
• Important dust sources in galaxies
• Bright populations in the infrared
• Quantitative analysis of AGB evolution based on
  observations

3
Questions

• Are AGB stars important populations for providing
  dust in the interstellar medium of galaxies?
• Influence of metallicities
• How far have we understood the stellar evolutions
  of the AGB phase?
• Are AGB stars responsible for infrared brightness
  of galaxies?

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Can dust be formed at low metallicities?Dust
needs (astronomical) metals!

• Carbonaceous dust
• Graphite C
• Amorphous C
• Polycyclic aromatic hydrocarbons (PAHs)

• Oxides
• Olivines Mg2xFe(2-2x)SiO4
• Pyroxenes MgxFe1-xSiO3

Dust mass as a function of metallicity of
galaxies It has been suggested that it is
difficult to form dust grains in stars in low
metallicity (Zlt0.1 Z?) galaxies
But we found unexpected results
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The Galaxies of the Local Group

• Some galaxies have low metallicities

Sculptor dwarf spheroidal (dSph) galaxy
Z/H-1.33
Fornax dwarf spheroidal galaxy Z/H-1.0
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Spitzer spectra
Amorphous Carbon
SiC
Sculptor dSph galaxy Z/H-1.33 Sloan, Matsuura
et al. (2009, Science 323, 353)
Fornax dSph galaxy Z/H-1.0 Matsuura et al.
(2007, MNRAS 382, 1889)
Contrary to expectation, we detected dust in AGB
stars at low metallicity galaxies
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Dust at low metallicity

• AGB stars
• We detected amorphous carbon (SiC) dust
• Carbon atoms synthesized in AGB stars

• Dust formation process in stars is affected
• not only by the metallicity of the parent
  galaxies
• but also by elements formed inside stars, in
  particular, carbon
• Matsuura et al. (2005 AA 434, 691)

(Fornax and Sculptor dSph galaxies)
(Our Galaxy)
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Implications for high-z galaxies with dust

• Past explanation
• AGB stars have two problems in producing dust
• Age Low and intermediate stars have not reached
  AGB phase (only after 1 Gyrs)
• Older than age of high-z galaxies (0.3 Gyrs)
• Low metallicity It was difficult to form dust in
  AGB stars
• Solely SNe could produce dust grains
• Current explanation Sloan, Matsuura et al.
  (2009, Science, 323, 353)
• AGB stars can produce dust at high-z galaxies
• AGB phase starts earlier than previously thought
  (about 0.28 Gyrs at 3 M? Zgt8)
• Dust can be formed in AGB stars even at low
  metallicity
• A theoretical mode suggests that 50 of dust in
  the quasar SDSS J11485251 (z6.4) originates
  from AGB stars and other half from SNe (Valiante
  et al. 2009, MNRAS, in press)

Submm-galaxies (z6.4)
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Questions

• Are AGB stars important populations for providing
  dust in the interstellar medium of galaxies?
• Quantitive analysis
• How far have we understood the stellar evolutions
  of the AGB phase?
• Are AGB stars responsible for infrared brightness
  of galaxies?

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Observations of the LMC
Optical image

• AGB stars are dust embedded objects
• Analysis of IR emission gives dust expulsion rate
  per AGB star
• SAGE (Meixner et al. 2006)
• LMC(SMC) Spitzer imaging survey
• Entire AGB census
• IRAC 3.6, 4.5, 5.8, 8.0 micron
• MIPS 24, 70, 160 micron

3.6 micron blue 8.0 micron green 24 micron red
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Gas and dust injected into the ISM of the LMC
AGB stars are important dust sources
Matsuura et al. (2009 MNRAS 396, 918)
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Missing mass problem in dust budget

• Current LMC dust mass 2x106 M?
• HIH2 gas mass (8x108 M?) x dust-to-gas ratio
  (0.0025)
• Dust injection rate from AGB stars 4.3x10-5 M?
  yr-1 (up to 8x10-5 M? yr-1)
• requiresgt20 Gyrs Lifetime of the LMC (15 Gyrs)
• Dust lifetime was estimated to be 4-8x108 yrs
  (Jones et al. 1994) ? (2-6)x104 M?
• Dust deficit is short by a factor of 30-100
• Unaccounted cold dust in AGB stars / Other dust
  sources required in the LMC

SNe Dust formation? Shock destruction?
AGB dust (2-6)x104 M? over (4-8)x108 years
ISM dust 2x106 M?
Other dust sources are needed
Matsuura et al. (2009, MNRAS 396, 918)
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Questions

• Are AGB stars important populations for providing
  dust in the interstellar medium of galaxies?
• Influence of metallicities
• How far have we understood the stellar evolutions
  of the AGB phase?
• Parametrizations
• Are AGB stars responsible for infrared brightness
  of galaxies?

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Models meet observationsStep ahead after the
Spitzer observations

• Two chemical types of AGB stars abundance ratio
  of carbon and oxygen
• Oxygen-rich (C/Olt1)
• Carbon-rich (C/Ogt1)
• Enhancement of carbon abundance at the third
  dredge-ups during the AGB phase

In the process of fine turning of mass-loss rate,
i.e. affecting IR excess and age of the AGB stars
Large Magellanic Cloud Isochrones Marigo et al.
(2008, AA 482, 883) Obs Meixner et al. (2006,
AJ 132, 2268) Matsuura et al. (2009, MNRAS 396,
918)
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Parameterisation of AGB evolution(1)Empirical
formula of mass-loss rate of AGB stars

• Mass-loss rate determines the current mass of
  the AGB stars
• Luminosity vs mass-loss rate of the AGB stars
• LMC distance 50 kpc
• Stellar variability affects uncertainty of the
  luminosity
• Luminosity integration of observed flux from
  near-IR to mid-IR (but different variability
  phases)
• As a measured parameter, the period of
  variabilities is better than the luminosity of
  stars (c.f. period and luminosity relation)

Luminosity
Period
Groenewegen et al. (2006) Wood et al. (2007)
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Parameterization of AGB evolution(1)Empirical
formula of mass-loss rate of AGB stars

• Empirical formula
• Mass-loss rate vs color
• IR excessmass-loss rate

10-5M? yr-1
10-6M? yr-1
Mass-loss rate scale (carbon-rich AGB)
10-4 M? yr-1
Matsuura et al. (2009)
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Parameterization of AGB evolution (2) Age (
metallicity) Difference of populations

• Using field stars
• Advantage Large number of stars
• AGB star population is very small
• Disadvantages
• Contamination of other populations
• Uncertainties in age and metallicities

3.6 micron image of the Large Magellanic Colud
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Parameterization (2) Difference of populations
(age metallicity)
Bar (mainly 3-5 Gyrs) 820,000 objects
Disk (gt11 Gyrs 0.1 Gyrs) 350,000 objects
There is no high mass-loss rate AGB stars Only
low-mass AGB stars left
Low mass Initial mass lt1.5 Msun Age gt2.7 Gyrs old
Emission line objects WR stars etc (high mass /
young stars)

• High mass-loss rate AGB stars (thermal
  pulsating AGB stars) are dominant source of gas
  and dust refurbishment in the ISM
• AGB stars are important for chemical evolution
  at the age of 3-5 Gyrs

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Questions

• Are AGB stars important populations for providing
  dust in the interstellar medium of galaxies?
• How far have we understood the stellar evolutions
  of the AGB phase?
• Are AGB stars responsible for infrared brightness?

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Are AGB stars important for mid-infrared
flux/intensity of galaxies?

• Current very rough estimate from LMC bar/disk
  observations suggests
• AGB stars above tip of RGB branch (Thermal
  Pulsating (TP) AGB)
• F(AGB above tip of RGB)/F(below tip of RGB) at 8
  micron
• 0.17 in the bar (3-5 Gyrs)
• 0.10 in the disk (11 Gyrs)
• HII regions and YSOs are not counted
• Thermal pulsating AGB stars are the brightest
  population, and they contribute to increase
  integrated brightness of the galaxy in
  mid-infrared at 3-5 Gyrs
• However, it is difficult to calibrate actual
  contribution of TP-AGB stars using field stars,
  because of contaminations of foreground stars and
  early AGB stars in F(RGB)
• . These values do not mean that infrared
  brightness of galaxies with 1-5 Gyrs old
  population has originated from to AGB stars ..

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Summary

• AGB stars are important dust sources in galaxies
• After Spitzer observations, we are in the process
  to parameterise mass-loss rate during the AGB
  phase
• Constraints for AGB evolution
• It is still uncertain if low-and
  intermediate-mass stars are responsible for the
  mid-infrared brightness of galaxies with 1-5 Gyrs
• JWST AGB stars in different types of galaxies
  (e.g. elliptical galaxies, and galaxies with
  younger populations)